Term
| the more attenuation a structure has, the (whiter/darker) it will appear on CT |
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Definition
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Term
| Describe how a structure will appear on CT in terms of hounsfield units. |
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Definition
-Air, which appears black, has -1000 hounsfield units
-water, which appears grey, has 0
-muscle, which appears grey, has 10-40
-bone, which appears white, has 400 to 800 |
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Term
| On a CT of the heart showing pericardial effusion, how can one tell if the effusion is blood or water? |
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Definition
| By the attenuation and hounsefield units. The heart is muscle (10 to 40 HU), water is 0 HU so it will be blacker than the muscle, blood is 30-50 HU so it should be equal to or whiter than the heart muscle |
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Term
| What are the three basic window settings used by radiologists? |
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Definition
1. lung
2. bone
3. soft tissue/mediastinum |
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Term
| what is the radiation dose threshold for embryonic/fetal congenital malformations, miscarriage, mental retardation, and neurobehavioral effects? |
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Definition
> 200 mGy
this is equiv to 20 PE studies or 8 CT abd studies |
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Term
| Patients with a history of anaphylactoid reaction usually receives _______ before receiving IV contrast |
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Definition
steroids
32 mg methylprednisolone 12 and 2 hours before scheduled CT |
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Term
| What is a vasovagal reaction to IV contrast? |
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Definition
| increased vagal tone from procedure leads to hypotension and bradycardia |
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Term
| What is a chemotoxic effect of IV contrast? |
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Definition
| direct effect of the contrast agent on the organ (nephrotoxicity and CV collapse are 2 primary causes) |
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Term
| What are some examples of NOT real contrast reactions that patients may experience? |
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Definition
| warm sensation, metallic taste, sweating, nausea, vomiting |
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Term
| What is an anaphylactoid reaction to IV contrast? |
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Definition
| mimics allergic type reaction. INcludes hives and more serious reactions (throat swelling, stridor, perioral edema) |
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Term
| What are the three most important reasons to use IV contrast? |
|
Definition
1. improves the ability to distinguish between two areas of a CT scan- soft tissues
2. allows for intraluminal evaluation of vessels improving sensitivity for detecting dissection, thrombus/embolus, and vessel injury/tears
3. characterization of masses, primarily of hepatic, pancreatic, and renal origin |
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Term
| Should you ever CT the head? |
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Definition
| Not unless the patient has a mass in the brain and they cannot get an MRI. esp do not order contrast in the head. |
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Term
| Should you order contrast if you suspect a urinary tract stone? if the patient has borderline renal dysfunction? Follow up for a pulm nodule? |
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Definition
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Term
| What is the cut off for creatinine and IV contrast? |
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Definition
| Do not give contrast if the patient has levels >2.0 (unless on long term dialysis) without emergent indication |
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Term
| What does oral contrast do? What is it good for? |
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Definition
-distends bowel and allows visualization of luminal contents of the stomach, small bowel, and colon.
- good for etection of GI masses and cancers |
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Term
| Should you use or not use contrast to investigate bowel perforation? distinguishing bowels, ovaries and masses/abscesses in thin pts? appendicitis identification? |
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Definition
|
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Term
| What is the difference between positive and negative oral contrast agents? |
|
Definition
positive: attenuates x-rays and therefore is bright on CT-- it limits the evaluation of bowel wall pathology
negative: poorly attenuates x-rays and is dark on CT- allows for eval of bowel wall thickening in patients with suspected inflammatory or infectious bowel disease |
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Term
| At the 5 vessels level, veins are usually (anterior/posterior) to arteries |
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Definition
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Term
| what are three things you should definitely be able to label on a the 5 vessels level |
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Definition
| the lungs, trachea, and esophagus |
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Term
| What are three things that you should be able to point out at the aortic arch level? |
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Definition
aortic arch
SVC
azygous vein (which is entering the SVC) |
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Term
| What 4 things should you be able to identify at the aortopulmonary window? |
|
Definition
ascending and descending aorta
SVC
uppermost aspect of the left pulmonary artery |
|
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Term
| what is significant about the aortopulmonary window? |
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Definition
| in most people this is the space visible just underneath the arch of the aorta but above the pulmonary artery. its an important landmark because it is a favorite location for enlarged lymph nodes to appear |
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Term
| What 6 things should you be able to identify at the main pulmonary artery level? |
|
Definition
the main, right, left pulm arteries
the right and left main bronchi
bronchus intermedius |
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Term
| What 4 things should you be able to identify at the superior heart/ high cardiac level? |
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Definition
| left atrium, right atrium, aortic root, and R ventricular outflow tract |
|
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Term
| What 5 things should you be able to visualize at the inferior heart/low cardiac level? |
|
Definition
R atrium
R ventricle
L ventricle
pericardium
intraventricular septum |
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Term
| What are the lobes of the liver? |
|
Definition
| the R, L, and caudate lobes |
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|
Term
| How is the R lobe divided? The L lobe? |
|
Definition
R= anterior and posterior subdivisions
L= medal and lateral lobes, which are separated by the ligamentum trees and the falciform ligament |
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Term
| What vein courses along the posterior border of the pancreas? what artery courses along the superior border of the pancreas? the pancreas rests anterior to what artery? |
|
Definition
superior mesenteric vein
splenic artery
superior mesenteric artery |
|
|
Term
| which kidney is usually a little bit larger in adults? |
|
Definition
|
|
Term
| What are kidneys the major route for excretion of? |
|
Definition
| iodinated contrast material, they should therefore enhance whenever iV contrast is administered |
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Term
| Why is an adrenal CT almost always ordered? |
|
Definition
| to evaluate malignant potential of adrenal adenoma. a CT can not distinguish between the 2 different types of adenomas, it is only used to identify adenomas and exclude malignant potential |
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|
Term
| What is the adrenal protocol? |
|
Definition
non-contrast CT through adrenals (adenoma is HU<10)
portal venous CT through adrenals
delayed CT through adrenals |
|
|
Term
| An adrenal adenoma is diagnosed if one or both of the following is satisfied: |
|
Definition
1. HU of adenoma is <10 on non contrast CT
2. washout of contrast is >60% |
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|
Term
| What is the stone protocol? |
|
Definition
| non contrast CT of abdomen through the kidneys and bladder |
|
|
Term
| should contrast be used to visualize stones in the kidney? |
|
Definition
|
|
Term
| Why would a CT of the kidneys be ordered? |
|
Definition
-evaluate renal masses, distinguish between cysts and tumors
-thorough eval of renal vessels and urinary tract |
|
|
Term
| What is the renal protocol? |
|
Definition
non-contrast scan through the kidneys (fat, stones)
corticomedullary scan through kidneys (degree of enhancement of renal masses)
neophrogenic phase scan through kidneys (pyelonephritis)
delayed phase scan from kidneys through bladder (collecting system, ureters, bladder) |
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|
Term
| if a mass enhances on the corticomedullary phase CT of the kidney then it is usually ________ |
|
Definition
|
|
Term
| what is the best image to see a mass in the kidney? |
|
Definition
| nephrogenic phase- it will be dark on it |
|
|
Term
| Why would we use contrast in the pancreas? |
|
Definition
| easier to identify tumors and characterize masses, look for necrosis, look at ducts, look at vessels, look at nodes |
|
|
Term
| Why is a pancreatic CT usually ordered? |
|
Definition
| to assess known pancreatic masses- RARELY used for eval acute or chronic pancreatitis |
|
|
Term
| what is the pancreatic protocol? |
|
Definition
-non contrast CT through pancreas
-arterial phase CT through abd (ISLET CELL TUMORS!)
-protal venous phase CT through abd (ADENOCARCINOMA!) |
|
|
Term
| Why do we use contrast in the liver? |
|
Definition
| improves detection of masses, characterization of masses, detection of thrombi and cirrhosis, hepatic steatosis |
|
|
Term
| why is a liver CT ordered? |
|
Definition
| to identify and characterize liver masses |
|
|
Term
| what is the liver protocol? |
|
Definition
non contrast CT through liver (hepatic steatosis, identify cysts)
arterial phase CT through abd (arterial enhancing masses)
portal venous phase CT through abd (hypoenhancing hepatic masses and portal venous thrombosis) |
|
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Term
| A CTA of the abd/pelvis is scan timed to optimize what? |
|
Definition
| opacification of the aorta and visceral arteries (SMA, IMA, celiac, renal, iliac) |
|
|
Term
| why would we use contrast in a cTA of the abd/pelvis? |
|
Definition
-used to assess arterial extravasation (esp in trauma or GI bleed)
-identify thrombus/embolus
-quantify atherosclerotic dz
-identify acute aortic syndromes (dissection, intramural hematoma, and penetrating atherosclerotic ulcer) |
|
|
Term
| why would you want a coronal or sagittal reformat? |
|
Definition
|
|
Term
| IV contrast is administered in a peripheral vein then travels to the SVC/R atrium/R ventricle--> pulmonary arteries, when it hits the pulm arteries what phase is this? |
|
Definition
| CT PE/CTPA (CT for pulmonary embolism) |
|
|
Term
| .....pulm arteries---> pulm veins/L atrium/LV--->aorta/arteries: what phase is seen in the aorta/arteries and what other imaging protocol? |
|
Definition
CT angiography/CT dissection protocol
arterial phase images |
|
|
Term
| ....aorta/arteries----> organs/portal veins: what phase is seen in this step? |
|
Definition
|
|
Term
| .... organs/portal veins---> IVC/Veins: what phase is seen here? |
|
Definition
|
|
Term
| ...IVC/veins---> urinary tract: what phase? |
|
Definition
|
|
Term
| Contrast from the heart can reflux into the IVC, therefore it is best to assess the IVC in what view/study? |
|
Definition
|
|
Term
| When there is no contrast in the aorta or portal vein, what phase is it? |
|
Definition
|
|
Term
| When the contrast in the aorta is brighter than the portal vein what phase is this? |
|
Definition
| arterial phase (AKA angiographic phase b/c it is usually done as part of CTA protocols) |
|
|
Term
| When contrast in the portal vasculature is equal or brighter than the aorta, what phase is this? |
|
Definition
| portal phase (used for run of the mill CT abd/pelvis and as part of the liver, pancreas, adrenal, and renal protocols) |
|
|
Term
| When contrast can be seen in the collecting system, what phase is this? |
|
Definition
|
|
Term
| what is the venous phase used for? |
|
Definition
| only used for evaluating potential systemic venous thrombi |
|
|
Term
| is volumen contrast positive or negative oral contrast? |
|
Definition
|
|
Term
| why would we use non contrast to assess fat in the kidneys? |
|
Definition
| because with contrast there is volume averaging |
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