Gastrointestinal Flashcards
Liver spleen imaging agents
sulfur colloid
MOA of Tc99m sulfur colloid
taken up by eticuloendothelial cells (liver, spleen, bone marrow); specifically taken up by Kupffer cells in liver
rapidly cleared with half life of 2-3 minutes
Cause of photopenic defect on Tc99m sulfur colloid scan
hepatic cyst»_space; HCC, adenoma, abscess
be wary of HCC in pts with risk factors
FNH on sulfur colloid
FNH may
hyperconcentrate radiocolloid, also regenerating nodule in cirrhosis, or Budd Chiari syndrome (hepatic vein thrombosis)
What ist he colloid shift?
increased colloid accumulation in spleen/bone marrow; typically seen with liver dysfunction/cirrhosis
Causes for increased diffuse pulmonary uptake with sulfur colloid?
cirrhosis, COPD with superimposed infection, LCH, high serum albumin (excess antacids; excess aluminium)
diffuse pulmonary uptake on sulfur colloid scan
cirrhosis, COPD with superimposed infection, LCH, high serum aluminium
utility of sulfur colloid for intrapancreatic spleen
intrapancreatic spleen will show uptake; can also use Tc9mm damaged RBC
alternative scan to sulfur colloid for FNH
HIDA scan
FNH contains biliary ductules so should be positive on HIDA
NM scan for GI bleeding
Tc 99m RBCs made by in vitro mixing fo 1-3 mL of blood + stannous chloride and oxidizing agent; takes ~20 min
NM RBC study vs angiogram?
NM: identify bleeds as low as 0.2 mL/min vs 1 mL/min for angio
positive study will change shape/position over time due to peristalsis of intraluminal blood
NM study for Meckel imaging
Tc99m pertechnetate localizes to gastric mucosa
Positive meckel scan
increase activity usually in RLQ; lateral view also used to make sure it is anterior to ureter
Meckel diverticulum
remnant embryological omphalomesenteric duct; usually in distal ileum and can contain ectopic gastric mucosa
NM: HIDA
Tc99m iminodiacetic acid (IDA) analogs
disofenin: biliary system with bilirubin levels as high as 20 mg/dL; 90% uptake
mebrofenin: biliary levels as high as 30 mg/dL; 98% hepatic uptake
both taken up by hepatocytes, not conjugated
HIDA protocol
NPO for 6 hours, but must eat within 24 hrs
NPO > 24 hrs, CCK is given to empty gallbladder befoe radiotracer administered (give slowly 0.02 mg/kg)
begin imaging after injection; visualization = no acute cholecystitis
nonvisualization of gallbladder? give morphine and reimage 30 min (contracts sphincter of Oddi to redirect bile into cystic duct)
only give morphine if tracer is seen in small bowel; nonvisualization of small bowel is nonspecific for common bile duct obstruction
if morphine allergy; image at 4 hours
HIDA scan: normal
5 min: liver seen
15 min: radiotracer flow into cystic duct
tracer seen in small bowel; potent CBD
HIDA: acute cholecystitis
small bowel visualized but no visualization of gallbladder during course of exam (even after morphine augmentation)
HIDA: rim sign
increased hepatic activity surrounding gallbladder fossa; due to hyperemia, possible gangrenous cholecystisi
false positive HIDA
- recent meal/prolonged fasting
- CCK administered immediately prior to exam
- TPN
- pancreatitis
- severe illness
- chronic cholecystitis
- cholangiocarcinoma of cystic duct
false negative HIDA
gallbladder visualization with acute cholecystitis
- acalculous cholecystitis with patent cystic duct
- duodenal diverticulum simulating gallbladder (confirm with lateral view)
- biliary cyst simulating gallbladder
Chronic cholecystitis
difficult to diagnosis, even on HIDA
low gallbladder ejection fraction thought to be suggestive of chronic cholecystitis
compare pre/post CCK injection gallbladder counts
<35% ~~ chronic chole
assessing for biliary leak
HIDA scan
perform in right lateral decubitus to promote dependent pooling of bile
hepatic dysfunction on HIDA scan
IDA tracers actively transported into hepatocytes; severe hepatic dysfunction will cause poor uptake and blood pool clearance
hepatic mass will appear as focal photopenic defect
