CT- Abdomen and Pelvis Imaging Procedures
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why is oral contrast used?
to differentiate a fluid-filled loop of bowel from a mass or an abnormal fluid collection
what amount of oral contrast is desired?
at least 600 ml
when is the bladder best appreciated on CT?
when filled with urine or contrast agent
how do intravenous contrast agents improve the quality of studies of the abdomen and pelvis?
by opacifying blood vessels, increasing the CT density of vascular abdominal organs, and improving image contrast between lesions and normal structures.
multiphasic imaging is frequently used for specialized studies of which organs?
pancreas, liver, kidney as well as in many abdominal CTA protocols
in healthy subjects the attenuation of the liver in an unenhanced study is atleast how many HU (Hounsefield Units) greater than that of spleen?
what abnormality, which is one of the most common abnormalities diagnosed by liver CT, is indicated when the liver is 10 HU lower than that of the spleen?
fatty infiltration of the liver
what causes fatty infiltration of the liver?
alcoholism, obesity, diabetes, chemotherapy, corticosteroid therapy, hyperalimentation, and malnutrition
fatty infiltrate of the liver is accurately assessed on what type of CT study?
non contrast CT
what is a hemangioma?
- benign tumors that are also commonly found in the liver.
- majority of hemangioma cases are solitary but pts can have multiple lesions
how does a hemangioma appear on an unhenhanced CT?
as a well-defined hypodense mass of the same density as other blood-filled spaces, such as the IVC
how does a hemagioma appear on a contrast enhanced CT?
- the lesion shows progressive pooling of contrast in rounded or oval blood filled spaces at the lesion periphery
- in most cases, with further delay the lesion fills in slowly from the periphery, eventually becoming uniformly enhanced
- occasional lesions may not fill in completely, likely because of central thrombosis
where and how much does the liver gets its blood supply?
- hepatic artery - 25%
- portal vein - 75%
hepatic arterial phase occurs how long after contrast is injected?
15 to 25 secs
portal venous phase occurs how long after contrast is injected?
60 to 70 secs
Which phase does a routine abdominal CT or as part of a chest, abdomen, and pelvic study, scanned under?
portal venous phase (60-70 secs scan delay after contrast injection is initiated)
which phase are hypervascular tumors show the best enhancement?
late arterial phase (35-45secs)
which anatomical structures is the pancreas generally located between?
12th t-spine and 2nd l-spine
what protocol or timing phases is/are used for a ct pancreas?
- dual phase
- arterial phase (35-45 secs)
- portal venous (65-70 secs)
- thin cuts
Unenhanced CT of the kidneys and ureters is generally reserved to demonstrate what?
calculi and calcifications
what protocol or scan phases is/are generally used for evaluating renal mass?
- non con then one or more phases after IV contrast administration:
- corticomedullary phase (30-70 secs)
- nephrogram phase (80-120 secs)
- excretory phase (3 mins-15 mins or longer)
what is a CTU?
- CT urography- imaging of the upper and lower urinary tract
- uses MDCT with thin-slice imaging with IV administration and imaging in the excretory phase
what type of protocols or scan phases are used for a CTU?
Protocols may include only the excretory phase or may contain as many as four phases
what are the 4 scan phases that may be used for a CTU?
unenhanced, corticomedullary, nephrographic, and excretory
CTU uses single or split bolus?
either one is used
What occurs during a split bolus CTU?
- divide the contrast media dose into two bolus injections with a delay of 2 to 15 mins between injections
- the first injection is providing excretory phase opacification and the 2nd injection is providing renal parenchymal enhancement
- the goal of the split bolus is to image a combined nephrographic-excretory phase
what is the main advantage of a split bolus CTU compared to a single bolus?
adenomas or benign adrenal mass contains more or less fat compared to malignant adrenal masses?
- adenomas contain more fat
- malignant adrenal masses contain less fat
how can you differentiate between a benign adrenal mass to a malignant adrenal mass on CT imaging?
- benign mass has more fat meaning that it has low attenuation properties or low hounsfield units (-100 to -50HU). If an adrenal mass measures 10HU or less on an unhenhanced CT then it is benign
- if the mass is greater than 10HU then it's hard to characterized if its malignant or not
- administration of contrast can tell if its malignant or not by watching for contrast washout. Adenomas enhance rapidly with IV contrast, and the agent washes out rapidly. Metasteses also enhance quickly but retain the contrast longer.
what protocols or imaging phases are used for determining an adenoma from a malignant mass especially when the suspected mass is greater than 10HU?
non con, portal venous phase, 15 min delay
what is the washout percentage threshold specific to adenomas?
greater than or equal to 40% and greater than or equal to 60%
which anatomical landmark is the appendix located under?
which age group is most at risk for acute appendicitis?
10-40 yrs old
when can an acute appendicitis be life threatening?
when it ruptures before surgical treatment
what are the classic symptoms of a patient with acute appendicitis?
RLQ pain, abdominal rigidity, and migration of pain from the periumbilical region to the RLQ
which different areas can the appendix be located and what type of symptoms are associated with each location?
- the typical anterior position (right ASIS)- RLQ pain and tenderness
- retrocecal position (behind the cecum near the ilopsoas muscle)- flank pain
- hangs into the pelvis- pain in the suprapubic area and rectum.
what are the most common CT findings in acute appendicitis?
- dilated nonopacified appendix
- soft tissue stranding (inflammation) into adjacent periappendiceal fat
what kind of protocols are used in finding acute appendicitis?
- protocols vary from hospitals to hospitals
- procedures use different combinations of oral, rectal, IV or no contrast.
- protocols also differ regarding the anatomic area to be included in the scan
- the most widespread CT approach is to scan the entire abdomen and pelvis with both IV and oral contrast
what type of scanning protocol is used for renal stones?
- 2.5 mm-3mm helical non con scan
- scan from the top of the kidneys to the base of the bladder
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