Gastrointestinal

Question 1

Liver spleen imaging agents

Answer 1

sulfur colloid

Question 2

MOA of Tc99m sulfur colloid

Answer 2

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

Question 3

Cause of photopenic defect on Tc99m sulfur colloid scan

Answer 3

hepatic cyst&raquo_space; HCC, adenoma, abscess

be wary of HCC in pts with risk factors

Question 4

FNH on sulfur colloid

Answer 4

FNH may

hyperconcentrate radiocolloid, also regenerating nodule in cirrhosis, or Budd Chiari syndrome (hepatic vein thrombosis)

Question 5

What ist he colloid shift?

Answer 5

increased colloid accumulation in spleen/bone marrow; typically seen with liver dysfunction/cirrhosis

Question 6

Causes for increased diffuse pulmonary uptake with sulfur colloid?

Answer 6

cirrhosis, COPD with superimposed infection, LCH, high serum albumin (excess antacids; excess aluminium)

Question 7

diffuse pulmonary uptake on sulfur colloid scan

Answer 7

cirrhosis, COPD with superimposed infection, LCH, high serum aluminium

Question 8

utility of sulfur colloid for intrapancreatic spleen

Answer 8

intrapancreatic spleen will show uptake; can also use Tc9mm damaged RBC

Question 9

alternative scan to sulfur colloid for FNH

Answer 9

HIDA scan

FNH contains biliary ductules so should be positive on HIDA

Question 10

NM scan for GI bleeding

Answer 10

Tc 99m RBCs made by in vitro mixing fo 1-3 mL of blood + stannous chloride and oxidizing agent; takes ~20 min

Question 11

NM RBC study vs angiogram?

Answer 11

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

Question 12

NM study for Meckel imaging

Answer 12

Tc99m pertechnetate localizes to gastric mucosa

Question 13

Positive meckel scan

Answer 13

increase activity usually in RLQ; lateral view also used to make sure it is anterior to ureter

Question 14

Meckel diverticulum

Answer 14

remnant embryological omphalomesenteric duct; usually in distal ileum and can contain ectopic gastric mucosa

Question 15

NM: HIDA

Answer 15

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

Question 16

HIDA protocol

Answer 16

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

Question 17

HIDA scan: normal

Answer 17

5 min: liver seen
15 min: radiotracer flow into cystic duct

tracer seen in small bowel; potent CBD

Question 18

HIDA: acute cholecystitis

Answer 18

small bowel visualized but no visualization of gallbladder during course of exam (even after morphine augmentation)

Question 19

HIDA: rim sign

Answer 19

increased hepatic activity surrounding gallbladder fossa; due to hyperemia, possible gangrenous cholecystisi

Question 20

false positive HIDA

Answer 20

• recent meal/prolonged fasting
• CCK administered immediately prior to exam
• TPN
• pancreatitis
• severe illness
• chronic cholecystitis
• cholangiocarcinoma of cystic duct

Question 21

false negative HIDA

Answer 21

gallbladder visualization with acute cholecystitis

• acalculous cholecystitis with patent cystic duct
• duodenal diverticulum simulating gallbladder (confirm with lateral view)
• biliary cyst simulating gallbladder

Question 22

Chronic cholecystitis

Answer 22

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

Question 23

assessing for biliary leak

Answer 23

HIDA scan

perform in right lateral decubitus to promote dependent pooling of bile

Question 24

hepatic dysfunction on HIDA scan

Answer 24

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