UNLABELLED:Measurement of red cell mass with isotope dilution remains an important diagnostic test in the evaluation of patients with suspected polycythemia vera (PCV). Results and reference ranges are typically expressed in units normalized for body weight (mL/kg). Obesity is common in polycythemic patients, and it is important to know how the various published normative ranges compare across a wide range of body weights.METHODS:We retrospectively reviewed 51 consecutive patients referred for red cell mass determination with 51Cr red blood cell dilution. Results were expressed in milliliters per kilogram (mL/kg) by using the actual patient weight and after adiposity adjustments using ideal body weight, body mass index (BMI) and combinations of height-weight, including body surface area. Results were classified as normal, elevated or PCV.RESULTS:There was a high prevalence of obesity in our population (28/51 [55%] with BMI > 27 kg/m2, BMI range 16.0-54.8 kg/m2). The method used to compensate for obesity had a dramatic effect on the derived red cell mass, the fraction of patients with elevated measurements and the fraction of patients meeting criteria for PCV. Concordance for categorization as normal, elevated or PCV by all methods was only 47.1%.CONCLUSION:Obesity is a common confounding factor in the interpretation of red cell mass measurements. Currently published reference ranges generate inconsistent results when extrapolated to obese patients. Further normative data on obese subjects are needed to determine which method (if any) is optimal.

UNLABELLED Persistent or recurrent Graves' hyperthyroidism after an initial treatment dose of radioactive iodine (RAI) is not uncommon and usually necessitates additional administrations. The radiation sensitivity of the previously irradiated thyroid gland is unknown but is of importance in selecting the retreatment dose. METHODS A retrospective analysis of patients receiving RAI for Graves' hyperthyroidism was undertaken. A first treatment dose was given to 1076 patients, and 168 of these patients subsequently required a second dose for persistent or recurrent hyperthyroidism (interval between RAI treatments, 8.5 +/- 17.1 mo). RESULTS Paired comparisons for retreated patients showed similar RAI doses (291 +/- 95 MBq and 283 +/- 129 MBq; p = ns) and treatment intensities (3.26 +/- 1.87 MBq g(-1) and 3.48 +/- 1.88 MBq g(-1); p = ns) for first and second treatments. Hypothyroidism occurred significantly earlier and more frequently after the first RAI dose (p = 0.002), but there was no difference for persistent or recurrent hyperthyroid events (p = 0.14). Multivariate regression established that the RAI treatment number (first or second) was a significant independent determinant of hypothyroid (p = 0.008) and combined (p = 0.001) events, whereas RAI dose and dose intensity were not. CONCLUSION We conclude that previous RAI treatment failure does not lessen the chance of successfully eradicating Graves' hyperthyroidism with additional RAI treatment. Furthermore, the previously irradiated thyroid gland may be less susceptible to early hypothyroidism than the RAI-naive thyroid gland.

UNLABELLED:Patient motion remains a significant source of unsatisfactory cardiac SPECT examinations. The extent to which image recovery can be achieved with correction algorithms is unknown.METHODS:Nine subjects who had completed motion-free redistribution 201Tlcardiac SPECT subsequently underwent simultaneous dual-isotope (201Tl/99mTc) SPECT with a 99mTc cutaneous point source, while the imaging table was subjected to predefined nonreturning y-translation movements. Cardiac reconstructions, marker reconstructions and marker-compressed dynamic images were generated from the raw data after applying the following correction methods: diverging squares, cross-correlation of the cardiac data and cross-correlation of the marker.RESULTS:Marker cross-correlation performed significantly better than all other methods with good-excellent results in all evaluations. This compared with good-excellent results in none of 27 for the raw data, in 13 of 27 for cardiac cross-correlation and in 7 of 27 for diverging squares (p < 10(-5)). The superiority of the marker-based method was confirmed on analysis of bullseye difference maps and quantitation of residual motion in the point-source data.CONCLUSION:Motion artifacts can accurately be detected and corrected using cross-correlation of an external point-source. Furthermore, this technique provides useful independent information on the degree of image recovery.

A 57-yr-old woman was referred for preoperative scintigraphic localization of a parathyroid adenoma. Double-phase 99mTc-sestamibi imaging was performed followed by a separate-day [99mTc]pertechnetate thyroid scan. There was marked accumulation of both tracers by a right lower pole ¿thyroid' nodule which, at surgery, proved to be an intrathyroidal parathyroid adenoma. Hypervascularity is the presumed explanation for rare cases of pertechnetate-avid parathyroid adenomas.

The normal biodistribution of Tc-99m pertechnetate includes the thyroid gland, salivary glands, choroid plexus, and gastric mucosa. The primary route of excretion is through renal clearance. The authors describe two cases in which hepatobiliary excretion of intravenously administered Tc-99m pertechnetate was observed during scanning for Meckel's diverticulum as a possible source of gastrointestinal bleeding.

The authors describe two patients in whom parathyroid adenomas were successfully localized with a Tc-99m sestamibi/pertechnetate subtraction technique, but who did not exhibit differential sestamibi retention on delayed imaging. Although the frequency of this occurrence is unclear, it suggests that some parathyroid adenomas will be missed if reliance is placed on sestamibi retention alone without simultaneous thyroid imaging.

A case of pericardial abscess is presented. The cause is presumed to be perforation of the right ventricle during pacemaker wire insertion, resulting in an infected hemopericardium.