14.1 Gastrointestinal Procedures
Key Takeaways
- Gastric emptying uses standardized solid (egg-white sandwich) and/or liquid meals with geometric-mean anterior–posterior imaging at fixed times (classically 0, 1, 2, 3, 4 h solid)
- GE reflux imaging and liquid emptying protocols differ from solid solid-meal SOP—know meal type, positioning, and reflux markers when ordered
- GI bleeding scintigraphy with Tc-99m labeled RBCs localizes active bleeding; hemangioma studies use labeled RBCs with delayed SPECT/SPECT-CT blood-pool pattern
- Hepatobiliary (mebrofenin/disofenin) evaluates cystic duct patency and biliary kinetics; morphine contracts the sphincter of Oddi to fill the gallbladder; CCK (sincalide) measures GBEF
- Liver–lung shunt mapping uses arterial MAA for Y-90 planning; liver–spleen colloid maps RES; Meckel’s diverticulum uses Tc-99m pertechnetate for ectopic gastric mucosa
14.1 Gastrointestinal Procedures
Quick Answer: Gastric emptying = standardized solid/liquid meal + geometric mean timed images. Labeled RBCs = GI bleed and hemangioma. Mebrofenin ± morphine/CCK = biliary tree and GBEF. Arterial MAA = Y-90 liver–lung shunt. Colloid = liver–spleen. Pertechnetate = Meckel’s. Prep, timing, and QC decide whether the study is diagnostic.
Domain V GI items reward protocol fidelity: correct meal, times, adjunct drug, and standard processing—not free-form “looks empty enough.”
Gastric Emptying (Solid and Liquid)
Solid meal (standard teaching)
Society-standardized solid gastric emptying uses a low-fat egg-white sandwich meal (toast/jam/water per protocol) labeled with Tc-99m sulfur colloid cooked into the egg whites. Adult activity is typically ~0.5–1 mCi class in the meal. The patient must finish in a defined window (often ≤10 min); incomplete intake is documented and may invalidate reference ranges.
| Time point (solid, common) | Action |
|---|---|
| 0 h | Immediate post-meal anterior + posterior (or dual-head) images |
| 1, 2, 3, 4 h | Same geometry; report percent retained (or emptied) |
| Processing | Geometric mean of anterior and posterior stomach counts ± decay correction |
Geometric mean (√[Ant × Post]) reduces depth-dependent error as the meal moves in the abdomen. Draw a careful stomach ROI; exclude small-bowel activity already emptied. Delayed emptying = high residual at late times (protocol-specific cutoffs).
Liquid emptying and GE reflux
Liquid studies (Tc-99m sulfur colloid or DTPA in water/juice) empty faster; imaging intervals are minutes, not hours. Gastroesophageal reflux protocols image esophagus/stomach after a liquid or semi-solid meal, sometimes with binder or maneuvers per SOP. Do not apply solid reference ranges to liquid curves.
Prep traps: prokinetics or narcotics alter emptying; follow NPO orders; vomiting ruins quantification; motion and inconsistent camera distance bias counts.
GI Bleeding Scintigraphy (Tc-99m Labeled RBCs)
In vitro (preferred) or modified in vivo Tc-99m RBC labeling produces a blood-pool tracer that extravasates at active lower (and some upper) GI bleeds. Adult activity ~20–30 mCi class IV. Acquire flow if ordered, then sequential statics or continuous dynamic imaging for hours; delays catch intermittent bleeds.
| Tech priority | Why |
|---|---|
| Labeling efficiency QC | Free Tc → stomach/thyroid/kidneys mimics or masks bleed |
| Continuous/serial imaging | Intermittent bleeding is missed on sparse snapshots |
| Anatomic landmarks | Mark iliac crests; cover upper and lower abdomen as ordered |
| SPECT/CT when available | Localizes extravasation for surgery/angiography |
Positive teaching pattern: activity that appears, intensifies, and moves in a bowel pattern. Fixed vascular structures (aorta, bladder blood pool) are not luminal bleeds.
Hepatic Hemangioma (Labeled RBC SPECT)
Same Tc-99m labeled RBCs, different question. Early flow may be photopenic; delayed blood-pool planar + SPECT/SPECT-CT (often 1–2 h) shows progressive fill-in greater than surrounding liver—classic cavernous hemangioma. Confirm labeling QC; small lesions may be below SPECT resolution.
Hepatobiliary Imaging ± GBEF
Tc-99m mebrofenin (or disofenin) is extracted by hepatocytes and excreted into bile. Fast 2–6 h (not multi-day starvation that collapses the gallbladder). Adult activity often ~3–5+ mCi IV (higher if bilirubin elevated—protocol).
| Finding / maneuver | Teaching meaning |
|---|---|
| Gallbladder visualization | Cystic duct patent (supports against complete cystic-duct obstruction pattern when criteria met) |
| Nonvisualization of GB | Suggests cystic duct obstruction if liver and bowel activity appear on time |
| Morphine sulfate | Contracts sphincter of Oddi → raises biliary pressure → fills GB if cystic duct open |
| CCK / sincalide | Stimulates GB contraction; GBEF = (max − min)/max × 100% after infusion |
Give morphine only when ordered after protocol criteria (e.g., bowel seen, GB still absent). CCK infusion rate matters—too rapid causes spasm and invalid EF. Document last meal, opioids, and TPN. Your job for dyskinesia studies: correct infusion timing, GB ROI (not bowel), complete dynamics.
Liver–Lung Shunt Mapping (Arterial MAA for Y-90)
Before Y-90 microspheres, IR injects Tc-99m MAA into the planned hepatic artery territory. Image liver and lungs (planar ± SPECT/CT). Lung shunt fraction = lung / (lung + liver) counts (SOP geometry). High shunt may reduce or contraindicate Y-90 activity. Coordinate IR timing, assay MAA, image promptly, avoid free-Tc misread as shunt, and flag extrahepatic nontarget foci.
Liver–Spleen Imaging
Tc-99m sulfur colloid (IV, ~4–6 mCi adult class) is phagocytosed by Kupffer cells and splenic/RES marrow. Planar and SPECT/SPECT-CT map hepatomegaly, colloid shift, defects, and splenules. Do not confuse colloid defects with hemangioma blood-pool fill-in—different agents.
Meckel’s Diverticulum
Tc-99m pertechnetate concentrates in gastric mucosa, including ectopic mucosa in a Meckel’s (usually RLQ). Weight-based activity (~5–10 mCi adult class). NPO; optional H2 blockade per protocol. Dynamic abdomen ~30–60 min. Positive: focus appearing with the stomach, usually RLQ. Traps: ureter/bladder activity, recent barium, active bleeding.
GI Procedure Comparison
| Study | Agent | Core tech focus |
|---|---|---|
| Solid GE | Tc-99m SC in egg meal | Standard meal, 0–4 h, geometric mean |
| GI bleed | Tc-99m RBCs | Label QC, serial imaging, moving focus |
| Hemangioma | Tc-99m RBCs | Delayed SPECT blood-pool fill-in |
| HIDA ± GBEF | Mebrofenin ± morphine/CCK | Fasting window, adjunct timing, GB ROI |
| Y-90 planning | Arterial MAA | Lung shunt fraction, nontarget foci |
| Liver–spleen | Sulfur colloid | RES map, colloid shift |
| Meckel’s | Pertechnetate | Ectopic gastric mucosa focus |
Bottom line: GI nuclear medicine is meal standards, blood-pool labeling, biliary pharmacology, and arterial coordination—execute the protocol, then process with geometric means and honest ROIs.
Why is the geometric mean of anterior and posterior stomach counts used when processing a solid gastric emptying study?
A hepatobiliary scan shows prompt liver uptake and small-bowel activity at 60 minutes, but the gallbladder has not visualized. Morphine is ordered per protocol. What is the intended effect?
For Y-90 microsphere planning, Tc-99m MAA is injected into a hepatic artery catheter. What primary calculation does the technologist support with liver and lung imaging?