Week 6: CT Organ Specific Considerations Flashcards
Organ Specific Considerations for Liver
- Normal CT attenuation of the unenhanced liver is between 38 and 70 HU.
- Healthy liver is at least 10 HU greater than the spleen.
- Common findings in the liver: Fatty infiltrates
- Cavernous hemangioma
Assessment of Fatty Infiltration on Liver CT
- Lower than normal attenuation of the liver Use non-enhanced CT (C-)
- Many Techs include a ROI of the liver and of the spleen
- Indicated when liver ROI is at least 10HU lower than that of the spleen
Liver CM Timing
- Hepatic arterial phase: 15-25 seconds
- Portal venous (PV) phase: 60-70 seconds
- Equilibrium phase: Several minutes after
- Routine liver CT: scanned during PV phase.
- Multiphase scanning improves the sensitivity & has diagnostic benefit in specific cases.
Organ Specific Considerations of Pancreas CT
- Water or low-attenuation oral contrast are preferred because dense contrast may obscure small stones.
- If initial scan fails to differentiate the margins of the pancreas from the duodenum, the patient is given additional oral CM & slices are obtained with the patient in the right decubitus position.
Pancreas imaging
- CT is by far the best exam compared to plain films, ultrasound, GI studies with contrast
- Thin slices and IV contrast increases odds of seeing the main duct
- Multiphasic protocols are common for this region. Often use bolus tracking software
(Late arterial (35-40sec), Portal venous ( 65-70sec))
Organ Specific Considerations for Kidneys and Ureters
- MDCT (multi-detector CT) is the modality of choice for renal evaluation
- Most renal abnormalities best visualized with CM
- Unenhanced reserved for calculi or baseline
Multiphasic: Corticomedullary phase (30-70secs), Nephrogram phase (80-120secs), Excretory phase 3-15mins or longer
CT Urography
- Evaluates of the upper and lower urinary tract 12
- CT imaging for kidneys, ureters, bladder
- Consists of many different protocols (thin slices, IV CM, imaging on excretory phase. tailored to indication, may include 1-4 phases of enhancement)
- some us split bolt injection
- longer delay on excretory phase provides better opacifaction of distal ureters
- fairly high radiation dose
Single bolus CTU contrast administration
- 100-150ml @2-3ml/sec
- scanned at nephrographic base to asses renal parenchyma
- scan at excretory phase to asses urinary tract
Split bolus CTU contrast administration
- 2 doses (2 to15min apart)
- Patient scanned only once after 2nd injection (less radiation dose)
- goal is a combined nephrographic and excretory phase visualization
Organ Specific Considerations for Urinary Tract Calculi or Renal Colic
- terms used interchangeably: kidney stones, renal stones, renal calculi, nephrolithiasis, and urolithiasis
- 4 basic types of stones (calcium salts, uric acid, struvite & cystine)
Causes of Urinary Tract Calculi or Renal Colic
- UT Infections & kidney disorders (eg. Polycystic kidney)
- Metabolic diseases (eg. Hyperparathyroidism)
- Hereditary factors (in up to 45% of cases)
- Urine abnormalities (eg.Decreased volume, imbalanced PH, over excretion of stone constituents)
- Certain foods/diet (Only if susceptible to stones)
- Drug-Induced (Can precipitate in the urine…eg. Ant-acids containing magnesium silicate)
Diagnosis of Urinary Tract Calculi or Renal Colic
- starts with medical history followed by physical exam and urinalysis
- DI essential to confirm size, location, & to assess obstruction
- Non-contrast Helical CT (NCHCT) used because it is 99% accurate
Renal Stone Protocol
- Typically, helical, top of kidney to base of bladder, thin slices 3mm or less
- disadvantage is dose to gonads
Organ Specific Considerations for Adrenal Glands
CT is modality of choice for detection & characterization of masses
- “Incidentalomas”
- Technique of choice to differentiate adenomas vs. mets.
- Evaluates “contrast wash-out” of the mass on delayed imaging
Adrenals Glands imaging
On an axial image, characteristic Y, V, T shape
- Adrenal protocols attempt to characterize lesions
- goal is to reduce the number of biopsies & follow-ups. Improves diagnosis and cost of care.
- Intracellular lipid (fat) content: Any homogenous adrenal mass that is <10 HU on unenhanced CT is benign
- CM washout: Washout can only be evaluated if
delayed images are acquired, washout greater than 60%
indicates adenoma
