Gastrointestinal and Hepatobiliary Scintigraphy

Salivary Scanning

In conjunction iwth thyroid scan or intentional with Tc-99)4, lemon juice washed around mouth then immediate and delayed images. Sjogren syndrome or inflammation degrades secretory function. Wathin tumour hot on delayed as it is not drained by ducts. Salivagram – child’s mouth swabbed with tracer, delayed images of lungs to check for aspiration.

Oesophagus and Stomach

Oesophageal transit study – solutions or solid boluses of Tc-99m sulfur colloid (Tc-SC) swallowed, 50% sensitive for oesophageal dysmotility. Ant view, upper, middle and lower ROI; transit times calculated from time-activity curves. Normal shows no activity after 10s.Oesophageal transit study – solutions or solid boluses of Tc-99m sulfur colloid (Tc-SC) swallowed, 50% sensitive for oesophageal dysmotility. Ant view, upper, middle and lower ROI; transit times calculated from time-activity curves. Normal shows no activity after 10s.

Gastrooeosphageal Reflux. Acidified orange juice (reduces lower oeosophageal sphincter pressure and delays gastric emptying) mixed wih Tc-SC. ROIs over upper, middle and lower oesophagus and stomach with ROI over lung at end of study to check aspiration. In adults abdominal binder can sequentially increase abdominal pressure. 90% sensitive for GORD.

Gastric emptying dependent on neuoroendocrine processes, foot type, pH, fatty content, osmolality; impaired by diabetes, electrolyte disturbance, postvagotomy syndrome, medications, mechanical obstruction. Gastric motility assesed with solid or liquid labeled with tracer (in CHCH scrambled eggs), time-acitivy curve generated for stomach. Normal half-emptying time (T1/2) <90min for solids (biphasic withinitial lag phase followed by linear curve), <60min for liquids (exponential). Can be extended to study transit betw stomach and colon.

Carbon-14 urea breath test (C-14 UBT). Helicobacter pylori causes >90% duodenal and 80% gastric ulcers, increases risk of gastric carcinoma and lymphoma. Pt fasted, off antibiotics, bismut ahnd PPIs. C-14 labeled urea capsule given. H.Pylori contains urease converting into C-14 CO2, detected in breath (in NM department or central lab). Sensitivity 94%, specificity 98%.

Gastrointestinal Bleeding

In vitro Tc-99m0tagged RBC, continuous 1min dynamic frames over abdo and pelvis ant projection for at least 90min, or until bleeding point identified. Sensitive for bleeding at 0.1ml/min (vs CTA at 1mL/min). Should be done at time of suspected active bleeding. Can be repeated up to 24hrs of injection, but blood may have moved into colon on delayed. Positive bleeding is abnormal hotspot “out of nowhere”, persists and may increase with time and moves wtih peristalsis (antegrade, regrograde or both). Site of bleeding indicated where the hotspot first appears. Free Tc-99mO4 excreted by stomach, but none is free in tagged RBC. There may be unchanging blood pools in aorta, IVC, bladder or penis.

Meckel Scan

Meckel diverticulum contains ectopic gastric mucosa (mucous secretic cells which excretes Tc-99mO4, shown in midle or right lower quadrant in synchrony with stomach. May be enhanced with pentragstrin to stimulate uptake, or cimetidine to block outflow from the mucosa. Adults likely to have less or no gastric mucosa cf children.

Liver and Spleen

Liver/Spleen scan. Tc99m labed albumin or sulfur colloid which are phagocytoesd by reticuloendothelial cells: Kupffer cells in liver, reteiculendothelial cells in spleen; cells in bone marrow minimally seen. Poor specificity and hepatic lesions <1cm routinely missed. Liver lesions isointense or hotter than parenchyma include FNH (due to increasd concentration of reticuloendothelial cells), hepatic adenomas. Myelolipoma or extramedullary haematopoiesis are hot. Can evaluate spleen size configuration and position; hepatomegaly, normal variants (large left lobe ore Riedel lobe). “(Colloid) Shift” of activity to the spleen, marrow, lungs seen in alterations in perfusion and reticuloendothelial system function in cirrhosis, hepatitis. Liver/spleen scans can be subtracted from other NM studies to provide spatial information about these in relation to a suspected abnormality.

Heat-Damaged RBC Scan for Splenic Tissue. Preferentially extracted by splenic tissue, for diagnosis of polysplenia, splenosis, accessory splenic tissue.

Haemangiomas are photopenic on initial blood pool with delayed filling on 3hr scan, more intense than normal hepatic parenchyma. Best for lesiosn >10-20mm.

Hepatobiliary Imaging (Cholescintigraphy)

Tc-99m-inminidiacetic acid compounds include Tc-disofenin, Tc-mebrofenin, Tc-HIDA (lidofenin), are excreted unchanged into the biliary system (even in the presents of elevated serum bilirubin). Minimum 2hrs fasting. Anterior dynamic views should show prompt homogeneous uptake by liver with progressive reduction as it is excreted into the biliary system. Activity should be seen in major extrahepatic ducts, GB and SB within 1h.

Acute cholecystitis – nonvisualisation of GB at 1h or 4hr after injection, or 30min after morphine administration. Chronic cholecystitis when not seen at 1h, but see by 4hrs (sensitivity 98%, specificity 95%). IV morphine (1-2mg) raises sphincter of Oddi pressure, helping to push labeled bile into the GB and speen up a “normal scan” and allow true negative scans to be performed in those who have eaten (causing GB contraction). “hot rim sign” is band of increased activity aroudn GB fossa due to poor excretion of tracer from inflammed hepatocytes in acute cholecystitis, usually associated with gangrenous cholecystitis. A completely full, atonic GB (prolonged fasting) will not fill with tracer, hence can pretreat with analogs of cholecystokinin (CCK, short aciting stimulat of GB contraction). Other false positives include cholecystectomy, tumour obstructing cystic duct, agenesis of the GB.

Acalculous biliary disease includes chronic acalculous cholecystitis, cystic duct syndrome (noncalculous partial mechanical obstruction of the cystic duct with painful GB contraction) and GB dyskinesis, present with RUQ pain, fatty food intolerance and epigastric distress. CCK-assisted cholescintigraphy shows reduced GB contraction and reduced GB ejection fractuion (normal >35%).

Postop complications and traumatic bile leaks can be seen on excretion phase. Delay of >1hr in visualising bile ducts suggests obstruction or severe hepatocellular disease. Neonatal hepatitis can be distinguised from biliary atresia, in which labeled bile ever enters the bowel or GB (but may also not leave liver in severe hepatitis, hence may take 4-24hrs to check for bowel activity to exclude atresia).

Hepatic Blood Pool Scintigraphy

Tc-99m-labeled RBC can help in diagnosis of cavernous haemangioma. Flow study shows normal or decreased early uptake (tumours and inflammatory lesions usually increased). Subsequent delayed SPECt shows foci of increased activity. Sensitivity reduces when <1.5cm, greater organ depth, single-detector SPECT (cf multidetector); correlation with other imaging technique advised. High specificity, but ocassional false positives in colong and lung mets. <br>