* Anything that reduces noise increases Contrast resolution.
Contrast resolution of a CT scanner is not related to which of the following:
A. Focal spot size.
*Want everything large to reduce the inherent noise level. Focal spot size is the only thing that doesnt affect noise.
Spatial resolution is improved by:
A. Small detector size.
B. Small pixel size.
C. Small voxel size.
D. Small patient.
*small detector size, small pixel size, small voxel size, small focal spot size, High freq filter, and narrow pre detector collimator. Anything that gives you higher image noise improves spatial resolution.
Which of the following improve contrast resolution?
Anything that reduced image noise improves contrast resolution. Larger FoV increases the size of the pixels thus reducing image noise, improving contrast resolution.
The term_____describes the ability of a CT Scanner to differentiate objects with minimal differences in attenuation coefficients?
C. Contrast resolution.
Which of the following is reduced by the use of high KvP during CT?
C. Photoelectric Absorption
C. Xray tube loading.
Bean hardening is also reduced.
Abdominal Aorta bifurcates at the level of :
D. L4: where if bifurcates into the left and right common iliac artery. Caude Equina is also located at the level of L4
The spinal coard ends at L2.
After the injection of IV contrast for a CT of the brain; what area does not enhance?
D. Posterior Horns of the Lateral Ventricle
*this area contains cerebral spinal fluid and doesnt enhance.
Ct scanning of the liver for tumor evaluation should not be performed during which phase of contrast enhancement?
C. Equlibrium; its the lowest point of enhancement
*the order is as follows: Bolus, Non equilibrium, Equilibrium.
The hepatic Arterial phase occurs about ____ seconds after the start of the IV injection?
D. 20-40 seconds after injection.
The portal venous phase occurs at about ___seconds after the start of injection.
*Hepatic early arterial 20-40 seconds; Portal venous @ 60-90secs
Which of the following would not enhance during the first several minutes of a post contrast CT study of the neck?
C. Lymph Nodes
Which of the following is Considered to be Iso Osmolar contrast media?
The rest are all Non Ionic Low Osmolar Contrast media
Non Ionic Low Osmolar Contrast Media
Ionic High Osmolar Contrast Media
Radiation exposure and its potential harmful effects have a relationship that is termed_____in nature.
Certain hermfull effects of exposrue to diagnostic xrays, such as cancer formation and genetic mutations are said to be random or Stochastic in nature
Stochastic effects is one that has no threshold dose but increases in probability with increases dose.
Radiation dose index calculation that takes into account the variations in absorbption across the field of view due to beam hardening is termed
B. CTDI w
is calculated from measurements made with dosimeter positioned at the center and periphery of a phantom and accounts for the veriences in dose distribution due to the effect of beam hardening.
Amount of xray energy absorbed in a unit of mass is measured in ?
What is it?
Its is the Absorbe dose.
Type of tissue radiotion is deposited in?
Quantity of Absorbed radiation dose based on the radiosensitivity of a particular tissue is called?
It is the Effective dose
Measured in Seiverts
Approximate mesure of the dose received in a single section or slice?
Average cumilative dose to each slice within the center of a scan, consisting of multiple slices; including scatter radiation.
Moderate reaction to contast media
*moderate to severe urticaria
*tachycardia from hypotension
Severe reaction to contrast media
Normal unenhanced liver density measures?
unenhanced density of 45-65
Peak arterial phase for the liver?
Peak arterial enhancement of the liver is 25-35 secs after injection.
*hepatic arterial supply well opacified
*no parenchymal enhancement
-for early arterial is 15-20
When does the Portal Hepatic venous Phase occur?
-60-70 seconds after injection.
-peak hepatic parenchyma enhancement.
-contrast redistributes from blood into extravascular spaces.
-demonstrates hypervascular lesions such as hepatic mets.
When does the liver equilibrium phase occur?
- 2-3 minutes after injection
-hepatic parenchymal enhancement dissipitates
-minimal difference in contrast between intra/extavascular spaces
- many lesions become indistinguishable between surrounding tissue.
When does the liver delayed phase occur?
5-20 minutes after injection
-demonstrates the complete fill in of a hemangioma as it becomes isodense with the surrounding parenchyma
When does the corticomedullary phase occur?
- late arterial phase 30-40 seconds
-optimal enhancement of the renal cortex/vein
-medulla minimally enhanced; allowing maximum differentiation from renal cortex.
When does the nephrographic phase occur?
-70-90 secs after injection
-enhancement differences between renal cortex and medulla reach equillibrium
-optimal for lesions.
When does the excretory phase occur?
-delayed imaging phase; 3 minutes after injection
-contrast agent becomes excreted into the renal calyces;opacifying the renal pelvis, ureters and bladder.
-visualized filling defects.
When does the arterial phase of the Kidneys occur?
* 20-25 secs delay; maximum opacification of the aorta/renal arteries.
What is effective mAs?
What is the formula for the effective mAs?