GUESS WHO 4-16-2006...

[chris_mason]

Not sure if you have seen these Curt....

Use of Diffraction Enhanced Imaging to Determine the X-ray Refractive Indices of Various Tissues at Biologically-Relevant Energies
Matthew Teng
Cornell University
Advisor: Zhong Zhong, Ph.D.
Brookhaven National Laboratory

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This experiment used diffraction enhanced imaging (DEI) to investigate the refractive indices of various organic tissues and water at X-ray energies similar to the energies of medical X-rays. We employed Silicon 333 reflection, which is typically used in DEI. In order to measure the small change in refractive index accurately across different samples and different energies, we constructed a sample holder which confined the sample to a 90-degree wedge. We analyzed the experimental data to determine the refractive indices for several organic tissues and water, and then we fitted them to a theoretical model. Clearly, each substance has a different refractive index. However, all substances showed the same inverse relationship between the energy and refractive index. This information will aid integration of DEI into clinical medicine in terms of optimization of DEI parameters in a clinical setting.


Introduction

Diffraction enhanced imaging (DEI) is a relatively new X-ray imaging technique which provides a very high contrast X-ray image of a subject using a single, monochromatic X-ray energy (Johnston et al. 1996). We used diffraction enhanced imaging in a research program aimed at studying the refractive indices of various organic tissues. This project was undertaken in order to further understand and investigate the possible introduction of DEI into a clinical medical imaging modality. This research was conducted at the X15A beamline at the National Synchrotron Light Source (NSLS) at the Brookhaven National Laboratory (BNL).

The underlying basis for DEI functionality exploits the unique atomic structure of perfect crystals. Synchrotron X-ray radiation produces high-powered X-rays covering an energy range of a few keV to a few hundred keV. A crystal monochromator is placed in the path of the X-ray beam, which is used to select a small energy range from the incident white X-ray radiation (Zhong et al. 2002). As a result, only X-rays with appropriate wavelength and energy are selected by the monochromator. Furthermore, an additional crystal, the analyzer crystal, is placed behind the sample. The purpose of the analyzer crystal is to reduce the scattering of the X-ray beam, which results from the elastic and inelastic (including Comption) scattering of the beam as it passes through the subject. The analyzer crystal also converts the differences in refraction angle, which result from the interaction of the electrons in the subject with the X-rays that pass through the sample, into a difference in intensity. As the radiation diffracted by the analyzer strikes the detector, it forms an image that is sensitive to the X-ray refraction. This difference in intensity permits a much greater degree of image contrast of the sample. As the X-rays strike the varying internal structure of the sample, differences in intensity result due to the varying thicknesses and densities of internal structure.

The DEI experimental setup allows for an improved radiological image with increased contrast when compared to the standard X-ray imaging techniques currently employed throughout the medical field. As a consequence, with the use of DEI, it is possible to image and distinguish among various types of soft tissue. The current X-ray imaging technology does not possess high enough contrast (at reasonable X-ray dosages) to distinguish among the relatively density-similar soft tissues. When the X-ray beam strikes the sample, there are two possible results that are relevant to DEI. That is, the X-rays can be absorbed, scattered, or refracted (Chapman et al. 1997). If the radiation is absorbed, then the intensity difference due to differences in sample absorption creates the absorption contrast. This contrast mechanism is the only contrast in conventional X-ray imaging, is well understood and provides one mechanism of contrast between different substances. However, as stated before, the X-rays can also be refracted. X-ray refraction properties are only measured and reported for a few inorganic materials, typically for 8 keV X-rays, which are too low for clinical imaging. Thus, in order to properly integrate DEI technology into clinical use, the refractive indices at high X-ray energies are needed to accurately build a digital model of various organic tissues. This could possibly provide an easier method of imaging soft tissue.

Theoretically, it is possible to measure the refractive indices of X-rays by directly measuring the deviation of the beam as it passes through the sample (James 1948). Practically, since the deviation from unity of the X-ray refractive index is very small, on the order of 10-6, the deviation of the beam is too small to be accurately measured (on the order of microns). Thus, an experimental method was developed to take advantage of DEI analyzer’s high angular resolution, on the order of micro-radians, to accurately measure this small angular deviation. Using the DEI technique, along with the proper calibration procedure and algorithm, it was possible to determine the absolute value of refractive indices of a few different types of tissues. The method used in this investigation can be easily adapted to other tissues in future studies.


Methods and Materials

This investigation took place at the X15A beamline at NSLS at the Brookhaven National Laboratory. See Figure 1 for experimental setup (Zhong 2002).Figure 1. The most popular SCI model is the rodent contusion model, with a necrotic core surrounded by histologically normal-appearing myelinated fibers and portions of grey matter from both dorsal and ventral horns (left). Similar to human SCI pathophysiology, the cell loss continues radially in all directions, so that the lesion expands over time. By 60 days post-SCI, there remains only a thin rim of white matter (right). Massive cell death, causing irreversible damage, occurs immediately after the initial impact in the central core region. However, cell death continues to occur over several days and weeks and offers an opportunity for therapeutic intervention to rescue the neural cell populations that are at risk of dying after the first few hours (Hulsebosch 2002). (Click image for larger version)

The design of the sample holder is schematically shown in Figure 2. It consists of a rectangular cell culture dish, with each compartment measuring approximately 10 mm in width. We used a total of 7 compartments in this experiment, and each compartment was filled with a different material. Each divider was approximately 1 mm in width. Figure 2. Corticospinal tract (CST) sprouting across the midline in the spinal cord after adenoviral vector neurotrophin 3 (Adv.EF -NT3) transduction of motoneurons. Dark-field photomicrographs of spinal cord cross sections showed the unlesioned CST axons. (A) Section from a normal rat (sham surgery). (B) Section from an Adv.EF -LacZ-treated rat (control vector). (C) Section from an Adv.EF -NT3-treated rat. CST neurites can be seen arising from the intact CST, traversing the midline, and growing into the gray matter of the lesioned side of the spinal cord. (A'-C') Higher-power photomicrographs of the regions around the central canal (Zhou et al. 2003). (Click image for larger version)

The cell culture dish was set up in such a way that the dish’s edges were 45 degrees off of the horizontal and the X-ray beam (Figure 3).

The bottom edge of the dish and the support strut were fixed into place using Devcon 5-minute epoxy. After we set up the sample-containing apparatus, we placed it into the experimental chamber and subjected it to DEI rocking curve measurement. The X-ray imaging beam was approximately 80mm in width. The energy points that were used for this experiment were 30, 32, 34, and 36 keV. We calibrated the energy of the X-ray beam using the K-edge of Iodine (33.169 keV) and then set by precisely controlled motors that functioned to tune the monochromator and the analyzer crystal. The beam was passed through a gas ionization chamber, whose purpose was to monitor the intensity of the oncoming beam. We used a shutter to control the exposure time of the sample. The sample was supported on a platform, which could be adjusted by a vertically moving linear stage controlled by stepper motor to accurately position the object in the path of the X-ray beam.Figure 3. Remyelination of the rat spinal cord following transplantation of adult human precursor cells. Normal (A), demyelinated (B), and remyelinated axons (C) of the dorsal column. (D) Remyelinated axons at higher magnification. The anatomical pattern of myelination was similar to that produced by Schwann cells (arrows). (bar: A–C, 25 µm; D, 10 µm) (Akiyama et al. 2001). (Click image for larger version)

For each energy that was used, two data sets were taken. One of the data sets was taken with the sample in the direct path of the beam (referred to as the “sample” set) while the other data set was taken with a sample placement outside of the beam, known as the “air” set, allowing for calibration. In an algorithm written later, the rocking curve peak position data derived from the air set was essentially subtracted from the sample set, thus reducing to a minimum the electronic noise interference and systematic error due to monochromator and analyzer crystal non-uniformity. During the data extraction, 56 scan lines were taken for every data set; the first 5 scan lines were taken with the shutter closed to measure the detector dark current, and the remaining 51 scan lines were taken with the shutter opened. Each data line was taken at different analyzer positions ranging from –5 to 5 micro-radians at a step size of 0.2 micro-radians.

Data analysis was conducted using an algorithm, written in IDL programming language that determined the refractive index of the tissue.


Results

Examining the experimental setup, it is possible to see the method of determining the refractive index of the organic tissue of interest (Figure 4).Figure 4. Schematic of a piece of spinal cord that has sustained an initial injury (black central oval) that spreads progressively outward and radially (red circular region followed by orange circular region) in zones until it finally reaches the final lesion size (grey shaded area). Blue lines are axons, and green rectangles are the myelinating oligodendrocytes. Methods of intervention: 1) reduction of edema and free radical production, 2) rescue of neural tissue at risk of dying in secondary processes such as abnormally high extracellular glutamate concentrations, 3) control of inflammation, 4) rescue of neuronal/glial populations at risk of continued apoptosis; 5) repair of demyelination and conduction deficits, 6) promotion of neurite growth through improved extracellular environment, 7) cell replacement therapies, efforts to bridge the gap with transplantation approaches, 9) efforts to retrain and relearn motor tasks, 10) restoration of lost function by electrical stimulation, and 11) relief of chronic pain syndromes (Hulsebosch 2002). (Click image for larger version)Considering the refraction at the left surface of the prism, it is apparent that

δΘ = Θ2 – Θ1

Using Snell’s Law:

n1 /n2 = sin Θ2 /sin Θ1


Therefore,

1/(1 – δ) = sin (Θ1+ ΔΘ)/(sin Θ1) [Equation 1]

where 1-δ is the refractive index of the material. The X-ray refractive index of the air is assumed to be 1.

Assuming for a small δ and δ Θ:

1 + δ = 1 + cot (Θ1)( ΔΘ) [Equation 2]

Therefore,

ΔΘ = [tan (Θ1)]( δ) [Equation 3]

Since the experimental apparatus was designed such that
Θ1 = 45 °
ΔΘ = δ

Considering this experiment, the X-ray beam was refracted at both the entering and exiting surfaces of the sample. Therefore,

ΔΘ = 2(δ)

Thus, the refractive index

δ = ½ (ΔΘ) [Equation 4]

As can be seen, the refractive index can be determined from simply measuring the angular deviation of the X-rays that pass through the material. This angle can be measured accurately by measuring the intensity-versus-angle curve (or rocking curve) of the analyzer crystal. As is known, the refractive index of any substance is energy dependent. In this investigation, we analyzed 7 substances at 4 different energies. These energies were 30, 32, 34, and 36 keV. This tunable energy range is similar to the X-ray energies that are generally used in clinical practice.

The first and second cells of the culture dish contained pork fat and chicken breast, respectively. The second, third, and fourth cells of the culture dish contained human breast parenchyma, human breast fat, and human breast fat along with skin, respectively. The tissues were provided by University of North Carolina Medical School with IRB approval. The sixth and seventh cells of the culture dish contained air and water, respectively. The data for the air chamber was used as a calibration to selectively eliminate the natural noise found in the experimental chamber. The deviation from unity, delta, of the refractive index was analyzed and determined for all substances (Table 1). Table 1. (Click image for larger version)


Discussion and Conclusions

Table 1 shows the absolute determined refractive index values of all the substances. Over the regulated energy range, the chicken breast has a higher index of refraction than the pork fat. This is to be expected, since chicken breast is a muscle tissue and muscle is typically more dense than fat.

These two tissues, chicken breast and pork fat, were used because they were the most generic muscle and fat tissues that were available. These results can be further used as models to serve future analysis. The composition of animal and human tissue is remarkably similar and thus the refractive index of those tissues can be assumed to be very similar and independent among species.

Over the regulated energy range, the breast fat and breast fat with skin refractive index values were comparable. This result is most likely due to the positioning of the skin in the compartment. The skin was placed alongside the closed end of the cell (Figure 5).Figure 5. (Click image for larger version)

The skin acts as a parallel plate, which serves to cancel the extra refraction due to the skin. Furthermore, human skin is very fibrous, and as a result, the skin is expected the scatter X-rays more than fat. However, since only the refractive index was measured in this experiment, we are not sensitive to scattering properties. Furthermore, the values of the refractive index of breast fat and pork fat are very similar. There is less than a 1.40% difference between the two different fats. This confirms the similarity in density, chemical composition and morphology of the same type of tissue among different species. The refractive index values of the breast tissue provide critical information for modeling a DEI system for mammography.

The refractive index of water under this energy range was very important to determine, since water constitutes nearly 70% of the human body and will almost always have an effect on the imaging procedure. The absolute refractive index values of water are considerably lower than every other organic tissue in this study. This is expected since water is much less dense than the organic tissues of interest in this study.

For low-Z materials, the deviation from unity, δ, of the refractive index is proportional to 1/E2. Z represents the number of electrons per atom. Using the measured values and a fitting procedure, it is possible to determine the refractive index value at any X-ray energy from the following formula.

δ = α * (1/E2) [Equation 5]

where α is a constant coefficient which is a unique property of the material. From Equation 5, it is apparent that δ is in a linear relationship with 1/E2. A linear regression analysis was applied to the experimental data and confirmed a statistically significant linear relationship between δ and 1/E2. The α value is proportional to the electron density of the specimen and E is the X-ray energy in keV.

Accordingly, taking all the obtained data from this experiment, it was possible to determine α for all substances used (Table 2). The α-values were determined by calculating the α-values of the individual experimental energies and averaging them to reduce experimental error. Averaging the α-values is a valid calculation because of the linear relationship of Equation 5.Table 2. (Click image for larger version)

Thus, using the determined α-values along with Equation 5, it is possible to predict the refractive index of an organic tissue at any desired energy. According to the theory, the refractive index, n, is (Zhong 2000)

1 – n = δ + iβ = (1/2π)reλ2 Σj (Nj + fj’ + ifj’’) [Equation 6]

where re = e2/mec2 = 2.818 x 10-15, which is the classic electron radius, and

λ is the X-ray wavelength.

Nj, zj, fj’ and fj’’ are the number density of atoms, the atomic number and the real and imaginary dispersion terms, respectively, for an atom j. The difference between the refractive index of the substance and that of a vacuum is (Guinier 1963)

δ = 1 – n = (1/2π)Nereλ2 [Equation 7]

where Ne = electron number density.
For the theoretical value, in the case of water,

Ne = 3.346 x 1023 electrons / cm3 = 3.346 x 1029 electron / m3

Using this value, it is possible to determine the theoretical α value of water by the following algebraic manipulation.

δ = 1 – n = (1/2π)Nereλ2 [Equation 7]

Using the approximation of λ = (12.4/E), in which λ is in Angstroms and E is energy in keV, we have

δ = 1 – n = (1/2π)Nere(12.4/E)2

δ = 1 – n = (1/2π)Nere(12.4)2*(1/E2) [Equation 8]

Previously stated,

δ = α * (1/E2) [Equation 5]

Thus,

α = (1/2π)Nere(12.4)2 [Equation 9]

Using Equation 9, the theoretical α-value of water is calculated as 2.31 x 10-4

Comparison of the theoretical water α-value with the experimental α-value led to a 26% discrepancy. This could be due to some experimental setup error. The experimental error was likely caused by the intrinsic variations of the samples. In other words, the samples were not homogenous throughout, which would affect the measurements. However, this error can be further minimized by averaging data over a larger area and by repeating measurements a few times to double-check the intrinsic texture variation.

The next step, which is already underway, is to incorporate the understanding of DEI contrast mechanisms into a clinical X-ray tube-based system. The currently employed X-ray conditioning (monochromator) and analyzer systems used at the National Synchrotron Light Source will be modified to suit an X-ray tube in order to deliver the flux necessary within a few minutes time. Brookhaven National Laboratory, in collaboration with the Illinois Institute of Technology, University of North Carolina, and Rush Medical School, is currently funded by the National Health Institute to carry out research to produce and test a prototype of a clinically-viable DEI system.

Ok, so what have you proven here relative to your argument?  Please read the last paragraph carefully before answering.

Chris

[zed]

TA if u really claim to eat all the shit u do it would have to be extemely small servings considering your basal metabolic rate. so u act like u eat wateva u want but in reality ur prob having a tblspoon of ice cream here and there due to its caloric density. especially considering what a little turd u are ur , for your calories to be in a deficit you are probably eating very close to if not under 2000? due explain..

[The True Adonis]

Adam...if you want to get into some sort of pissing match on that subject I will engage....but for the general MD/DC/etc....they will be using the standard x-tube with tungsten filament that is not intended for soft tissue scans....

Those are going to be obsolete. Mark My Words!

[sarcasm]

those pictures at the top of the thread show that all the talk about Adonis's legs being small are total bullshit, great development there.

[The True Adonis]

TA if u really claim to eat all the shit u do it would have to be extemely small servings considering your basal metabolic rate. so u act like u eat wateva u want but in reality ur prob having a tblspoon of ice cream here and there due to its caloric density. especially considering what a little turd u are ur , for your calories to be in a deficit you are probably eating very close to if not under 2000? due explain..

Actually for my body I am at a defecit at approximately 2981.612 calories.  That is without cardio and my basic routine such as work etc...

[zed]

those pictures at the top of the thread show that all the talk about Adonis's legs being small are total bullshit, great development there.

your name speaks volumes with this one...

[The True Adonis]

Actually for my body I am at a defecit at approximately 2981.612 calories.  That is without cardio and my basic routine such as work etc...

I can teach everyone their limit with my equation.
Alot of bullshit equations and methods out there.  But mine is EXACT.  

[zed]

I can teach everyone their limit with my equation.
Alot of bullshit equations and methods out there.  But mine is EXACT.  

lets see it dog

[250Ben250]

He is speaking on topis of which he is ignorant.  He is reaching...

Actually he is right about this, but most physicians wouldn't order a test like this (done for research, etc. only...)

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9313753&dopt=Abstract

Now where he's wrong is blaming all the fat gain on clean foods - TA don't flip flop on the point you're trying to make - weeks ago you're saying it doesn't matter what kind of food is eaten to get lean, a calorie is a calorie, etc. Now you're claiming that chicken breasts and oatmeal specifically made you as fat as you are in the first pics. This is why people ending up laughing at you in the end....

[The True Adonis]

Here is some more info Curt.

Scientists Image Soft Tissues With
New X-Ray Technique
Provides more information than conventional x-rays or other scanning methods
UPTON, NY — Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory, in collaboration with researchers at Rush Medical College, have demonstrated the effectiveness of a novel x-ray imaging technology to visualize soft tissues of the human foot that are not visible with conventional x-rays. The technique, called Diffraction Enhanced Imaging (DEI), provides all of the information imparted by conventional x-rays as well as detailed information on soft tissues previously accessible only with additional scanning methods such as ultrasound or magnetic resonance imaging (MRI). This study appears in the May 2003 issue of the Journal of Anatomy.

“We’ve previously shown that this technique can visualize tumors in breast tissue and cartilage in human knee and ankle joints, but this is the first time we have shown it to be effective at visualizing a variety of soft tissues, such as skin, cartilage, ligaments, tendons, adipose pads, and even collagen and large blood vessels,” said physicist Zhong Zhong, who works at the National Synchrotron Light Source (NSLS) at Brookhaven Lab, where the current work was done. “The ability to visualize such a range of soft tissues as well as bone and other hard tissues with just one technique has many potential applications in diagnosis,” Zhong said.

The technique makes use of the intense beams of x-rays available at synchrotron sources such as the NSLS. These beams are thousands of times brighter than those produced by conventional x-ray tubes, and provide enough monochromatic x-ray flux for imaging even after selection of a single wavelength.

In conventional x-ray images, the various shades of gray are produced because different tissues absorb different amounts of x-ray energy. “This works great in imaging bones and other calcified tissues,” said Zhong, “but less satisfactorily in imaging soft-tissues that have similar and low x-ray absorption.” In DEI, the scientists are more interested in the x-rays that pass through the tissue and how they bend and scatter as they do, because these properties vary more subtly between different types of tissue.


A conventional synchrotron radiograph of a foot (A) and the same foot shown with Diffraction Enhanced Imaging (B). Note the greater variety of soft tissues visible with in the DEI frame.

To analyze a specimen with DEI, the scientists place a perfect silicon crystal between the sample and the image detector. As x-rays from the synchrotron go through the sample, they bend, or refract, and scatter different amounts depending on the composition and microscopic structure of the tissue in the sample. Then, when the variously bent rays exit the sample and strike the silicon crystal, they are diffracted by different amounts according to their angular spread. So the silicon crystal helps convert the subtle differences in scattering angles produced by the different tissues into intensity differences, which can then be readily detected by a conventional x-ray detector. This results in extremely detailed images that are sensitive to soft tissue types.

For example, in the current study, a conventional radiograph of a human toe shows bones and a calcified blood vessel; except for the faint “shadow” of the surrounding soft tissues and calcification within a tendon, no other structures are visible. The DEI scan of the same specimen in the same position clearly shows skin, the fat pads beneath the bones, the blood vessel, the nail plate, and some tendons, which are clearly distinguishable from the surrounding connective tissue. Within one of the fat pads, even the organizational architecture of the collagen framework is visible. Moreover, the bones take on a three dimensional appearance because of the detail available in the scans.

In the current study, the DEI images were produced with a lower x-ray dose than that used for diagnostic x-rays and no contrast agent was needed, making the technique viable as a potential screening tool, said Zhong.

The scientists are still working on how to scale down the DEI design so that it can be used in a clinical setting. But they say this should be feasible and that the technique may eventually greatly enhance mammography and become increasingly important in the detection of other soft tissue pathologies such as osteoarthritis, breast cancer, and lung cancer.

Collaborators at Rush Medical College include Carol Muehleman, Jun Li, and Klaus Kuettner. This research was funded by the National Institutes of Health, GlaxoSmithKline, Inc., and the U.S. Department of Energy, which supports basic research in a variety of scientific fields.

Paper describing the research entitled "Radiography

[chris_mason]

Actually for my body I am at a defecit at approximately 2981.612 calories.  That is without cardio and my basic routine such as work etc...

What??? LOL!!! I haven't been this amused by a post in a LONG TIME!!!! How the heck can you make a statement about caloric requirements to the 1000th??? If you had ANY kind of understanding of the body you would know that is not possible at this time.

[sarcasm]

What fucking records would you be breaking delusional-boy?

ooooooh big talk coming from a guy who presses a MASSIVE three plates and a small cookie on each side of the Hammer Strength flat press, does swinging t bars with an ungodly 6 plates and pulls all of his deadlifts of the pins of the power rack, hahahaha, you're a BEAST!!!!!!!!!!!!!!!!!!!!!!!!!!

[Hedgehog]

What??? LOL!!! I haven't been this amused by a post in a LONG TIME!!!! How the heck can you make a statement about caloric requirements to the 1000th??? If you had ANY kind of understanding of the body you would know that is not possible at this time.

He's probably kidding.

YIP
Zack

[The True Adonis]

What??? LOL!!! I haven't been this amused by a post in a LONG TIME!!!! How the heck can you make a statement about caloric requirements to the 1000th??? If you had ANY kind of understanding of the body you would know that is not possible at this time.

Of course it is. Calorimeters are accurate.

[Krankenstein]

Those are going to be obsolete. Mark My Words!

Adam.....its not likely to happen any time soon.  Just like they thought decompression machine for discs were going to be the "wave of the future" with regard to spinal care.  Those things still have yet to drop under $70K.

Standard x-ray machines will be still be the way to go for most people opening clinics and such.  They can run $25K and under...and this is even with the auto-tech capabilities and with the much improved 14x36 buckies. 

Are you referring to this when you are talking about the x-ray:

Measuring body composition in overweight individuals by dual energy x-ray absorptiometry

Rhonda A Brownbill1 and Jasminka Z Ilichcorresponding author1
1School of Allied Health, University of Connecticut, Storrs, CT 06269, USA

Rhonda A Brownbill: brownbillr@cs.com; Jasminka Z Ilich: jasminka.ilich@uconn.edu

Received October 25, 2004; Accepted March 4, 2005.
   
Abstract

Background
Dual energy x-ray absorptiometry (DXA) is widely used for body composition measurements in normal-weight and overweight/obese individuals. The limitations of bone densitometers have been frequently addressed. However, the possible errors in assessing body composition in overweight individuals due to incorrect positioning or limitations of DXA to accurately assess both bone mineral density and body composition in obese individuals have not received much attention and are the focus of this report.

Discussion
We discuss proper ways of measuring overweight individuals and point to some studies where that might not have been the case. It appears that currently, the most prudent approach to assess body composition of large individuals who cannot fit under the scanning area would be to estimate regional fat, namely the regions of thigh and/or abdomen. Additionally, using two-half body scans, although time consuming, may provide a relatively accurate measurement of total body fat, however, more studies using this technique are needed to validate it.

Summary
Researchers using bone densitometers for body composition measurements need to have an understanding of its limitations in overweight individuals and address them appropriately when interpreting their results. Studies on accuracy and precision in measurements of both bone and soft tissue composition in overweight individuals using available densitometers are needed.
   
Background

Dual energy x-ray absorptiometry (DXA) is widely used by clinicians and researchers for evaluation of bone status and soft tissue composition. While the principles of DXA technology could be found elsewhere [1-3] and are not the focus of this report, we address them briefly for better understanding of the discussion to follow. The underlying principle of DXA is its ability to quantify the attenuated radiation after its passage through bone and soft tissue using either K-edge filters or pulsed power sources to the x-ray tube. Subsequently, the differential attenuation of the two energies is utilized to quantify bone, lean, and/or fat tissue. The earlier DXA series are based on pencil-beam absorptiometry, where a highly collimated x-ray beam and a detector move along the rectilinear scan path. The new series employ fan-beam absorptiometry in which data are acquired either simultaneously along the entire scan line, or as rectilinear scanning with a narrow fan-beam, both resulting in a faster scanning time [1]. The fan beam densitometers have the advantage of improved geometrical resolution, but the disadvantage of errors induced by magnification effects. Within the fan beam instruments, the true fan beam densitometers have greater accuracy and precision, shorter scan time, and wider scan field than limited-angle fan beam densitometers which have inherent overlap in acquisition, smaller number of detectors, and poorer image quality [3].

The three major commercial manufacturers of bone densitometers are GE Medical Systems Inc. (former Lunar), Madison, WI; Hologic Inc., Waltham, MA; and CooperSurgical (former Norland Medical Systems, Inc.), Trumbull, CT. Although each of these companies employs a subtly different technology, our further discussion does not address the particulars of each technology and/or manufacturer. Our focus is the positioning of the overweight patients when obtaining densitometry scans and subsequent analyses of these scans, overlooked in many studies. However, for more information, the main physical characteristics of the most commonly used manufacturer/instruments are presented in Table 1.

DXA is considered one of the most precise technologies in clinical medicine when the measurement of bone mineral density (BMD) is considered, with the typical coefficients of variation between 1–2% [4]. Nevertheless, there are some limitations in BMD assessment as well. Results of in vitro and in vivo studies indicate different manufacturers, models, software versions and modes of analysis of densitometers can lead to variations in the assessed BMD and bone mineral content (BMC) in the same individuals [5,6]. Laskey et al (2004) found that the GE Lunar Prodigy gave significantly higher BMD, BMC and t-scores compared to the GE Lunar MD in 10 volunteers [6]. They also found that an increase in tissue depth (as in overweight individuals) caused an increase in the measured BMC and BMD for the MD model but not the Prodigy model, even when using the appropriate and same scan modes [6]. The prudent way to overcome these flaws would be to use the same instrument and software version throughout a single longitudinal study.

The accuracy of DXA instruments for measurement of soft tissue is also questioned due to various methodological limitations. Some of the limitations are addressed in a recent review [7] and are generally attributed to the hardware (fan- or pencil-beam) or software versions [8]. DXA instruments from different manufactures are shown to give considerably different soft tissue assessments of the same individual [9]. Lunar and Hologic are shown to give major differences in measurements of total body and regional body fat in HIV patients (2.4–13.4% higher values for Hologic) and in body fat distribution [9]. Additionally, individuals' hydration levels may affect calculations for soft tissue [7] whereas tissue thickness may affect beam magnification, especially if the proper scan mode is not chosen and in cases involving changes in subject's weight [10]. Also, estimates for soft tissue in regions directly adjacent to the large bony areas such as the trunk, arms and head, may result in decreasing precision. During the total body scans (to obtain body composition analysis) a larger pixel size is utilized and pixels that include smaller portions of bone may be counted as lean tissue [10]. Despite the above flaws, DXA can still be used for fairly accurate assessment of soft tissue composition or its change [7], particularly for groups and large-scale epidemiological studies, provided that its limitations are considered and adequately accounted for. However, it has to be noted that DXA technology is not approved by Food and Drug Administration for the individual assessment of body composition.

Currently, the most accurate method for measuring body composition is considered to be the four-compartment (4C) model in which fat free body tissue is divided into its constituent parts, namely water, protein and mineral. The 4C model then incorporates independent measurements of mineral, total body water and body density to derive body fat. The 4C model (though not a true gold standard) is often used as a criterion method to compare the accuracy of other methods for assessing body fat. This method however, is costly and time consuming and therefore not generally used in clinical settings. DXA (a two-compartment method) does not measure body water, which limits its accuracy in body composition assessment. However, since DXA offers quick and easy body fat assessment and is considered superior to many other methods, it is often used in clinical settings. Gately et al. [11] compared various body composition methods for assessing body fat in overweight and obese children. They found air-displacement plethysmography and DXA to be the most promising methods for body fat assessment in a clinical setting [11]. A study in non-obese women found DXA to be superior to waist circumference and waist-to-hip ratio in predicting intra abdominal fat [12].

The use of DXA for assessment of body composition in overweight/obese individuals increased recently due to numerous weight reduction studies. While all of the above limitations of bone densitometers have been frequently addressed, the limitations of assessing body composition in overweight individuals due to incorrect positioning and subsequent failures to properly analyze the obtained scans have not received any attention and are the focus of this report. We discuss proper ways of measuring overweight individuals and assessing their soft tissue and point to some studies where that may not have been the case.
   
Discussion

Use of bone densitometers in weight loss studies
In weight loss studies where DXA is used to evaluate lean and fat tissue, overweight/obese individuals range widely in body weight and size [8,13-20]. However, the maximum size of a DXA scanning table is limited to about 193–197 cm length and 58–65 cm width, with weight limitations from 114–159 kg depending on the manufacturer and model, Table 1. In order to fit an overweight individual within the scanning area, rice bags and straps are used to press the limbs as close to the body as possible [2]. Despite these measures, some large individuals cannot fit within the global region of the scan area. Additionally, in some cases, the space between the scanning table and the detector is not large enough to accommodate individuals with a larger chest girth, making their measurements difficult or impossible.

While some authors do address these limitations when reporting their data [14], some do not describe or vaguely describe DXA assessment [13,15,17,19] or are unclear regarding precision of their instruments in overweight individuals [15-18,20]. In our own preliminary studies with overweight women using a Lunar pencil-beam densitometer, the coefficients of variation (CV) for different skeletal sites ranged from 0.6–1.8% [21], but those for the soft tissue were higher reaching 8.2% for fat tissue in the arms (not published). The high %CVs (range 3.1–4.3%) for fat tissue (even in normal-weight individuals) were reported by others using pencil-beam instruments [22]. Figure 1 shows a total body scan of a 104 kg woman where portions of the arms fell out of the scan area, and therefore, could not be included in the analysis of the total body soft tissue. Furthermore, since her limbs were pressed against the sides of her body, overlap of tissue occurred in the chest, arm and hip regions, resulting in inaccurate regional soft tissue analysis (namely, trunk, legs and arms). Figure 2 presents the proper positioning and analysis of total body composition in a 59 kg woman. It is obvious that the inclusion of subjects who do not fit in the global scan area might lead to questionable accuracy of both total and regional soft tissue estimates.

Total body and regional soft tissue assessment
When total body soft tissue assessment is the goal, it is necessary to include all parts of the body in the scanning area. In overweight subjects, overlapping of body parts may affect the total results due to increased thickness in overlapping regions. Another source of error is the head, where tissue type cannot be distinguished. Specifically, the brain tissue cannot be measured by DXA due to the surrounding skull – it has to be assumed. Therefore, the assessment of soft tissue in this region is subject to large error and it is suggested the head be excluded from total body soft tissue analysis [10]. In regional assessment, DXA utilizes the placement of standard cut-lines to assess the arms, legs and trunk (chest, abdomen, pelvis), Figure 1 and 2. Each regional estimate may be subject to error in overweight individuals (in normal-weight ones too) if overlapping of regions occurred. Wang et al. [13] measured total and regional body fat with DXA in women (mean ± SD weight, 96 ± 11 kg) before and after weight loss. Since the positioning of the subjects was not described, it is not known whether all subjects fit within the scan area and whether tissue overlap occurred. Similar uncertainty exists in other studies [18,19].

In the newest study by Sun et al. [20] researchers compared the assessment of total body fat by multi-frequency bioelectrical impedance with DXA measurements as the "gold standard". The subjects in the study ranged in weight from 45 to 157 kg, with body mass index (BMI) ranging from 17 to 55 kg/m2, indicating some were severely obese. However, authors did not address the positioning or fitting of the obese subjects on the scanning table, therefore it could only be speculated about the adequacy of these measurements/analyses.

Researchers have found estimates of abdominal fat tissue by DXA to be similar to computed tomography (CT) and MRI-derived measurements in normal and overweight individuals of wide age range, indicating DXA can accurately estimate abdominal fat [24-26]. The abdominal region is not a routinely defined region by DXA software and therefore, must be manually determined (see Figure 1), which can differ among research sites. Park et al. [24] compared abdominal adipose tissue measured by MRI and DXA in non-obese men. They defined DXA regions of interest in two different ways (between the second-lumbar vertebra and the fourth-lumbar vertebra, or iliac crest) and found both of these regions comparable with MRI total abdominal adiposity and with MRI-derived narrow abdominal slices. Bertin et al. [26] reported DXA yielded accurate measurements of abdominal adipose tissue compared with CT in overweight/obese individuals weighing 66–134 kg. They manually defined DXA abdominal region to range from the acromion to the iliac crest, a slightly different placement than the ones described above, and compared it to a 10 mm region at the fourth-lumbar vertebrae measured by CT. It is important to note that the abdominal regions of interest could be subject to potential error if the upper limbs are positioned in too close contact with the trunk, causing the overlap of the regions.

Researchers have also found estimates of different regions of leg soft tissue extracted from the total DXA scans to be reliable in elderly subjects of wide weight range [8,26,27]. Similarly, fat tissue of the thigh determined by DXA was comparable to CT derived measurements in normal and overweight individuals. Tylavsky et al. [8] compared CT derived measurements of lean and fat tissue with DXA measurements of a manually defined sub-region of the mid-thigh (one-half the distance between the knee joint and the top of the femur, see Figure 1). They indicated a good assessment of soft tissue change by DXA in that region. It therefore appears that with large individuals, DXA should be used for assessing body composition of defined regions such as the mid-thigh or abdominal rather than the total body.

Half-body DXA scans for the assessment of soft tissue
Tataranni and Ravussin [28] suggest measuring soft tissue of obese individuals by scanning only one side of the body. They found total body composition results from right and left sides only differed minimally in both overweight and normal-weight individuals. The half-body scan can be performed by placing the central line of the scanning area through the midpoint of the left or right collar bone for each half-body scan. During analysis of the half-body scans, the central line is then repositioned on each half scan, and the side of the body that was not completely included in the scan area is deleted. The authors found that small errors in estimates of soft tissue can occur from imperfect positioning of the central line by the operator or by true anatomical differences between the left and right sides of the body. To minimize these errors, they suggest fat tissue be determined by multiplying percent body fat from the half-body scan by body weight, and lean tissue be determined as the difference between body weight and estimated fat tissue. Another possibility for improving accuracy of soft tissue assessment would be measuring both halves of the body, and then adding them up. However, more research on the above methods is necessary in order to make recommendations

Total body bone mineral assessment in overweight individuals
Similarly to problems with soft tissue assessment, there are problems with bone mass assessment when DXA is used in overweight individuals. When an individual does not fit within the scan region, there is subsequent loss of soft and bone tissue. Additionally, some anomalies in bone mass measurement during weight loss studies using different instruments were reported earlier [29]. Tothill et al. [29], re-analyzed published results of changes in total body bone mineral during weight change. The authors found weight change leads to considerable anomalies in measuring changes in bone mineral in all three brands of DXA machines (Hologic, Lunar and Norland), with the most serious ones occurring with Hologic [29]. These inaccuracies were suspected to be due to the use of different software modes (enhanced vs. standard) and the different assumptions manufactures make regarding fat distribution [29]. Phantom studies using Lunar and Hologic fan beam scanners showed bone mass measurements were not compromised by magnification effects, however, the height of bone and changes in body weight simulated with lard did affect the accuracy of BMD and BMC measurements [30]. Tothill and Hannan [30] compared Lunar and Hologic DXA fan bean scanners for measuring total body bone and soft tissue. Phantom measurements revealed that both fan beam instruments were subject to minor magnification effects, and measurements of BMD and BMC were both dependent on the height of a bone [30].

Summary

Current bone densitometers are limited to a scanning area that cannot accommodate some overweight/obese individuals. Newer fan-beam densitometers have a wider scan field [3] or can accommodate individuals up to 159 kg, Table 1, making them a better option for body composition assessment. Unless researchers are using some of the newer densitometers (with a scan table large enough to accommodate larger body sizes) they may need to rely on estimates of regional fat, namely the thigh or abdominal region when assessing the body composition of many overweight subjects. Using one or two half-body scans may provide a relatively accurate measurement of total body fat, however, more studies using this technique are needed. The results of some published studies in overweight/obese individuals need to be interpreted with caution, since they may have included subjects who could not properly fit within the scan area. Researchers using bone densitometers for body composition measurements need to have an understanding of its limitations in overweight individuals and appropriately address the stated concerns when interpreting their results. Authors also need to provide details of their DXA instrument including the manufacturer, the software version and the analysis mode used for body composition assessment when reporting their results. Studies on accuracy and precision in measurements of both bone and soft tissue composition in overweight individuals, using available densitometers, are warranted and needed.
   
Authors' contributions

RAB wrote article drafts and evaluated the cited literature. JZI conceptualized the idea and the design of the article, revised the manuscript and completed the final version. Both authors read and approved the final manuscript.

[chris_mason]

Actually he is right about this, but most physicians wouldn't order a test like this (done for research, etc. only...)

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9313753&dopt=Abstract

Now where he's wrong is blaming all the fat gain on clean foods - TA don't flip flop on the point you're trying to make - weeks ago you're saying it doesn't matter what kind of food is eaten to get lean, a calorie is a calorie, etc. Now you're claiming that chicken breasts and oatmeal specifically made you as fat as you are in the first pics. This is why people ending up laughing at you in the end....

Look, just because the jackass did a Pubmed search and posted something which is essentially irrelevant to the argument doesn't mean he is right???

Come on!  

[zed]

I can teach everyone their limit with my equation.
Alot of bullshit equations and methods out there.  But mine is EXACT.  

lets see the equation my main man....

[chris_mason]

ooooooh big talk coming from a guy who presses a MASSIVE three plates and a small cookie on each side of the Hammer Strength flat press, does swinging t bars with an ungodly 6 plates and pulls all of his deadlifts of the pins of the power rack, hahahaha, you're a BEAST!!!!!!!!!!!!!!!!!!!!!!!!!!

Sarcasm, you are a goof and you know it.  Tell you what, when I am at the Olympia hanging with the strongest men in the world we will discuss your thoughts on the matter...

[250Ben250]

those pictures at the top of the thread show that all the talk about Adonis's legs being small are total bullshit, great development there.

Yes TA truly shows advanced mass and definition in his legs here...

[The True Adonis]

lets see the equation my main man....

I will only help those who really are interested in wanting help.

[250Ben250]

Look, just because the jackass did a Pubmed search and posted something which is essentially irrelevant to the argument doesn't mean he is right???

Come on!  

Of course not, it just means he's a jackass that can search pubmed 

[Hedgehog]

Of course it is. Calorimeters are accurate.

How do you know that?

YIP
Zack

[The Luke]

Adonis,

There is no way you are 40% bodyfat in those pics... I hope you're exaggerating for emphasis.

At most you are somewhere between 18% and 25% bodyfat.


If you're 240 lbs in those pics, then you could expect to get down around 7% (contest shape) at a bodyweight of 180ish (allowing for muscle loss)

The Luke

[zed]

I will only help those who really are interested in wanting help.

im interested black

[Krankenstein]

This is from the Massachusetts Technology Transfer Center

Method and System for Body Composition Analysis Using X-Ray Attenuation http://www.masstechportal.org/IP984.aspx