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27 terms

4. CT Scan

STUDY
PLAY
CT Scan
Computed tomography
two types
Helical
spiral
Four densities
still apply
Hounsfield Units
measure of relative density (WATER IS ZERO) (Air<Fat< Water< Soft Tissue< Calcium< metal)
By adjusting the gray scale level one can...
differentiate between the ventricles of the heart
IN ANOTHER WINDOW
detail the air ways of the lungs
Post-processing******
Multiplanar reformatted images
(spiral processing)
sagittal
coronal
3-D Images
digitally take out everything that is not bone
Scan Parameters
Anatomy: Brain, Neck, Chest, ABD, pelvis, bone
Contrast: Oral, IV, other (rectal, bladder)
Slice Thickness: (0.6-10mm)
Scan Timing: breath hold, arterial, venous, delayed phase
Be able to ID the type of contrast:
IV contast vs Oral contrast
IV contrast: the density within the aorta will be similar to that of the vertebrae
Oral contrast: you will see difference in the tissue within the observable intestine.
Pre contrast
you see the kidneys
Post contrast
30 sec post
one can see the parenchyma
delayed
one can see the draining into the ureters
**** Enhancing (Solid) renal mass
an increase in H.U (density) from pre to post contrast

*** PRE contrast required
Renal cell carcinoma...
until proven otherwise
Hepatic Vein drains into the
IGC
Is CT sensitive enough for gall stones?
NO!!!! (ok sometimes)
they are the same density as the fluid around them

***Ultrasound is much better for this DX
HYPOdense lesions in the spleen
multiple lesions lymphoma
If air density is found in tissue that is in bubble form all over...
necrotizing fasciitis
brain sand is in the
pineal gland
Glioma
A tumor of the Brain
CT Angiography
Inject intravenous contrast
obtain scan during the arterial phase
Helical CT (volumetric Data)
Post- Processing
CT Angiograph can evaluate:
AORTA
PULMONARY ARTERIES CAROTID ARTERIES PERIPHERAL VASCULAR SYSTEM CIRCLE OF WILLIS
CTA
CT Angiograph
CT- Guided interventional Radiology
use images to guide procedures that would normally require surgery
Cardiac CT
MULTIDETECTOR (64 SLICE) SCANNERS SUB-MM SLICE THICKNESS EKG GATING

CORONARY ARTERY CALCIUM SCORING CORONARY ARTERY CTA
Coronary artery Calcification Scoring
Amount of Calcium in the coronary arteries is proportional to the overalll amount of atherosclerotic plaque.
Quantitative measure of this
calcium gives an assessment of risk for significant stenosis
Does NOT directly measure the degree of stenosis. NO evaluation of cardiac function.
Report Total Score
Plaque burden
Percentile