Lean Body Mass Assessment: Interpretations of Computed Tomography Sarah Peterson MS, RD, CNSC...
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Lean Body Mass Assessment: Interpretations of Computed Tomography Sarah Peterson MS, RD, CNSC Clinical Dietitian Rush University Medical Center Chicago,
Lean Body Mass Assessment: Interpretations of Computed
Tomography Sarah Peterson MS, RD, CNSC Clinical Dietitian Rush
University Medical Center Chicago, Il
Slide 2
Learning Objectives Upon completion of this session, the
learner will be able to: 1.Summarize the principles of measurement
for computed tomography 2.Describe the benefits and limitations of
diagnostic abdominal computed tomography to measure body
composition 3.Interpret abdominal computed tomography results
Slide 3
Computed Tomography (CT) Imaging
Slide 4
Computed Tomography Benefits Gold-standard imaging method
(along with MRI) for body composition analysis at the tissue-organ
level Diagnostic abdominal CT scans are frequently completed among
patients requiring nutrition support Sequential diagnostic
abdominal CT scans can be used to measure change in body
composition Limitations The radiation dose is significant, exposing
a healthy population to this level of radiation for the sole
purpose of body composition is unreasonable Quantification of
muscle and fat volume requires appropriate software and
training
Slide 5
Computed Tomography CT imaging Series of cross-sectional images
Process: X-ray source rotates Detectors opposite from the x-ray
source measure the strength of the x-rays exiting the section body
Repeated, section by section Images reconstructed by a
computer
Slide 6
Computed Tomography Final CT scan - multiple cross-sectional
images or "slices" of anatomy like the slices in a loaf of
bread
Slide 7
Computed Tomography CT slice thickness, thin (1 to 10 mm) and
uniform Each slice composed of 2-dimentional pixels 2-dimentional
pixel corresponds to 3-dimentional voxel (cross-sectional area x
area between slices)
Slide 8
Computed Tomography Each pixel within the matrix is assigned a
number that is related to the linear attenuation coefficient (or
loss of intensity) of the x-ray beam Hounsfield units (HU)
Comparison of x-ray tissue attenuation to equal volume of water
Water is abundant in body and has uniform density Water is assigned
an arbitrary value
Slide 9
Computed Tomography HU are converted into a gray scale High
numbers/tissue more dense than water (bone, organs & muscle) =
light gray/white Low numbers/tissue less dense than water (like air
and fat) = dark gray/black
Slide 10
Muscle SubQIntraMusc ular Visceral Computed Tomography
Diagnostic CT scans to examine muscle quality Typical features:
Muscle volume consistent with normal anatomy Will appear light gray
throughout Clearly visible demarcation between muscle and fat
depots
Computed Tomography Concerning features: Difficult to
distinguish muscle from visceral and subcutaneous adipose
tissue
Slide 15
Computed Tomography Concerning features: High content of
intramuscular fat (looks as if areas of muscle are missing)
Slide 16
Computed Tomography: Summary Diagnostic abdominal CT scans are
often ordered for patients receiving nutrition support These images
can be used to: Review muscle volume and quality Concerning
features include: thin/wasted muscle volume difficult to
distinguish muscle from visceral and subcutaneous adipose tissue
high content of intramuscular fat Describe rates of sarcopenia
Measure changes in muscle and adipose volume
Slide 17
Learning Assessment Question 2. Quantifying muscle pixels at
the third lumbar (L3) vertebra region on an abdominal computed
tomography represents a)L3 muscle cross-sectional area b)L3 muscle
volume c)L3 muscle volume and intra-muscular adipose volume d)Total
body muscle