Pediatric renal iodine-123 orthoiodohippurate dosimetry.

Radiation exposure to the kidney from iodine-123 orthoiodohippurate ([123I]OIH) and any associated [124I]OIH contamination may vary by a factor of several hundred depending upon the health of the kidney. Calculations of kidney dose were made for patients with the following renal states: normal, acute tubular necrosis (ATN), obstruction, and renal transplant. The dosimetry was based on a minimum practical administered activity (MPAA) of 200 microCi for pediatric patients and 500 microCi for adults. High-grade obstruction of recent onset and severe ATN are the only disease processes which could result in high exposures, and this is due primarily to the contribution of 124I. For selected cases, OIH labeled with pure 123I should be very seriously considered.

Contribution of contaminant indium-114m/indium-114 to indium-111 oxine blood dosimetry.

Indium-114m and 114In appear as contaminants in commercial preparations of [111In]oxine at a level of about 0.05% at time of calibration (TOC). The contribution of these contaminants to the radiation absorbed dose from [111In]oxine leukocyte, platelet, and erythrocyte imaging procedures has been evaluated. When the absorbed dose from these contaminants is expressed as a percent of the 111In dose to the same organ from a given procedure, the contaminants contribute an additional 0.16 to 12% of the 111In dose, and in one case, that of the spleen from [111In]oxine labeled erythrocytes, they contribute an additional 33%. Commercial samples of aqueous-based [111In]oxine contain levels of 114mIn/114In sufficient to result in a mild to moderate increase in the absorbed radiation dose to the patient. Strict quality control procedures must be maintained by suppliers to prevent higher contamination levels. It is advisable to avoid using 111In products of this nature later than about 3 days after the time of calibration.

Simultaneous technetium-99m MIBI angiography and myocardial perfusion imaging.

Resting first-pass radionuclide angiography (FPRNA) was performed with the myocardial perfusion agent technetium-99m MIBI. In 27 patients, it was compared with technetium-99m diethylenetriamine pentaacetic acid FPRNA. A significant correlation was present in left (r = 0.93, p less than 0.001) as well as right (r = 0.92, p less than 0.001) ventricular ejection fraction measured with both radiopharmaceuticals. In 13 patients, MIBI derived segmental wall motion was compared with contrast ventriculography. A high correlation was present (p less than 0.001), and qualitative agreement was found in 38/52 segments. In 19 patients with myocardial infarction a significant correlation was present between MIBI segmental wall motion and perfusion scores (p less than 0.001). In ten patients with a history of myocardial infarction, 18 myocardial segments demonstrated diseased coronary vessels and impaired wall motion at contrast angiography. These segments were all identified by the MIBI wall motion and perfusion study. We conclude that MIBI is a promising agent for simultaneous evaluation of cardiac function and myocardial perfusion at rest.

Intraarterial use of sodium methohexital for provocative testing during brain embolotherapy.

PURPOSE AND METHODS: To assess its vascular effects and safety, we used sodium methohexital (Brevital)--an ultrashort-acting barbiturate--as the provocative intraarterial agent in a series of 30 patients with arteriovenous malformations at a 1% concentration and at doses of less than 5 mg per injection. Digital vascular imaging was performed just prior to and just after the injections. RESULTS: No angiographic or clinical evidence of apparent vasospasm occurred in the trial population (66 vascular pedicle injections in 30 patients). When functional tissue was perfused with 1-6 mg of the 1% Brevital solution, evidence of altered neurologic status became immediately apparent, but cleared within 2 minutes in all cases. None of the patients experienced either prolongation of the induced clinical symptoms or seizures to suggest any adverse effects related to either crystallization of the Brevital or the effects of injecting an alkaline solution in the cerebral circulation. CONCLUSION: Though the full effects of methohexital in the cerebral circulation remain to be elucidated, existing reports suggest it is a safe provocative agent for use prior to embolotherapy for brain arteriovenous malformations.

Dosimetry of leukocytes labeled with 99Tcm-albumin colloid.

Biodistribution, kinetics and dosimetry of 9Tcm-albumin colloid labeled leukocytes (TAC-WBC) is described. A practical method of planar image data acquisition and processing is discussed. This method was used to obtain biodistribution data in 11 patients, two of whom were children. Dosimetry was calculated for fetuses, children and adults. The spleen is the critical organ, receiving 2.5 rad per 5 mCi procedure in adults and 3.6 rad per 2.15 mCi procedure in a 5-year-old child. These absorbed doses are about one-sixth of that absorbed from 111In-leukocytes procedures utilizing one-tenth the administered activity of TAC-WBC. The liver and red marrow are approximately equivalent secondary target organs, each receiving about 20% of the spleen dose. Fetal doses at any stage of gestation are similar, averaging about 14 mrad per mCi of TAC-WBC administered to the mother. The dosimetry of TAC-WBC is favorable enough to permit its use in children, adults and during pregnancy.

Pulmonary imaging in pregnancy. Maternal risk and fetal dosimetry.

A Tc-99m macroaggregated albumin (MAA) perfusion lung scan and a Tc-99m DTPA aerosol ventilation scan were performed for suspicion of pulmonary embolism (PE) in a patient who was ten weeks pregnant. There was considerable reluctance on the part of the obstetricians to permit this study. Standard MIRD dose estimates to the fetus were performed, which showed a maximum fetal exposure of about 50 mrem. It was concluded that the risk to mother and fetus from undiagnosed and untreated PE is much greater than the negligible risk to the fetus from the radiation exposure; fear of fetal radiation damage should not be a deterrent to performing these scans.

Technology for FDG SPECT with a relatively inexpensive gamma camera. Work in progress.

PURPOSE: At the time of the co-development of a commercial dual-headed gamma camera for whole-body single photon emission computed tomography (SPECT), modifications were made to permit imaging of 511-keV photons (from positron emitters) while maintaining versatility and cost-effectiveness in nuclear medicine for routine nonpositron studies. MATERIALS AND METHODS: Special collimators were made, and gantry stability was increased. Detector shielding and crystal thickness were not changed. In phantoms, healthy volunteers (two men, aged 34 and 38 years), and 109 patients (71 male and 38 female patients, aged 2-74 years [mean, 56 years]), SPECT was performed with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG). In patients, 36 myocardial viability, 47 oncologic, and 26 brain examinations were performed. RESULTS: All FDG SPECT scans were subjectively judged to be of acceptable quality. Preliminary results in regard to diagnostic findings are reviewed; this analysis is intended to be a feasibility study not a conclusive review of imaging accuracy. CONCLUSION: FDG SPECT provides images that are interpretable for cardiac or oncologic diagnosis, without the need for or expense of a positron emission tomography (PET) center or a dedicated PET scanner.

New technique for localization of therapeutic emboli using radionuclide labeling.

A sensitive method for localizing the resting place of catheter-injected therapeutic gelatin emboli is described. Surgical gelatin (Gelfoam) is labeled with 99mTc and each embolus observed on the persistence scope of a gamma camera after injection. This technique reduces the chance of obstructing blood vessels other than those intended. Two cases of embolization, one arterial and one venous, are illustrated.

Phagocytic labeling of leukocytes with 99mTc-albumin colloid for nuclear imaging.

A procedure is described for the phagocytic labeling of white blood cells (WBC) with high specific activity 99mTc--albumin colloid (TAC). The preparation contains approximately equal activities of granulocytes and monocytes. Heparinized whole blood (40 cm3) yields a preparation containing a total of 148-222 MBq (4-6 mCi) TAC-WBC including about 20% free TAC. The complete preparation time is 75 min. Imaging is completed 30 min to 4 h post administration of the TAC-WBC. Quality control methods and imaging protocols are described.