Reproducibility of volume-adjusted bone mineral density of spine and hip from dual X-ray absorptiometry.

Skeletal size has a confounding effect on areal bone mineral density (aBMD) related to differences in skeletal volume. Several methods have been proposed for calculating volumetric BMD (vBMD), but in vivo precision data are limited for the spine and have not been published for the hip. We prospectively performed duplicate dual X-ray absorptiometry measurements of the anteroposterior spine and hip (n = 121) in a diverse female population referred for initial clinical BMD testing. Each scan pair was performed and analyzed by two different technologists (mean interval of 4 d) to obtain standard aBMD. Scan data were reprocessed at a later date to calculate vBMD for the lumbar spine (L2-L4), femoral neck, and total hip in the 87 spines and 82 hips for which we had complete analyzable scan data. We found much worse precision in femoral neck volume (5.2% coefficient of variation [CV]) than in spine volume (2.6% CV; p < 0.003). This contributed to greater error in femoral neck vBMD (3.9% CV) than aBMD (2.3= CV; p < 10(-6)). Total hip aBMD had better precision than vBMD (1.0 and 1.3-2.5% CV; p < 10(-5)). The reverse pattern was seen in the spine with slightly better precision for vBMD than aBMD (1.1 and 1.5% CV; p < 0.002). Volumetric measures of lumbar spine density can be obtained with high precision. Because of poor reproducibility in the femoral neck, the total hip region may be preferable for measuring volumetric bone density in the proximal femur.

Effect of obesity on red cell mass results.

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.

Radioiodine treatment outcomes in thyroid glands previously irradiated for Graves' hyperthyroidism.

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.

Comparison of motion correction algorithms for cardiac SPECT.

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.

Technetium-99m-pertechnetate uptake by intrathyroidal parathyroid adenoma.

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.

Hepatobiliary clearance of intravenous Tc-99m pertechnetate.

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.

Parathyroid adenomas without sestamibi retention.

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.

External reference markers for the correction of head rotation in brain single-photon emission tomography.

Accurate reorientation of brain single-photon emission tomography (SPET) is required for quantitative procedures and for correlation with other imaging modalities. Traditionally, brain SPET has utilized reoriented slices parallel to the orbitomeatal line (OML). Reorientation using internal landmarks would be more convenient but has not been systematically compared with the use of external landmarks. We compared the interobserver reproducibility for defining the sagittal and coronal angular deviations using internal landmarks, a visual method based upon external reference markers, and an automated method based upon external reference markers. Internal landmarks were inaccurate for defining the OML whether this was based upon the frontal-occipital or frontal-cerebellar plane. External reference markers resulted in significantly lower interobserver differences for both sagittal and coronal reorientation. An operator-independent implementation proved to be feasible and provided an objective measure of marker coplanarity. In summary, external reference markers should be used when reproducible reorientation and ROI placement are required.

The diagnosis of thyroid disease on bone scans.

Three cases are reported in which visualization of the thyroid occurred during Tc-99m pyrophosphate bone scans. All were found to be hyperthyroid with elevated serum thyroid hormone and two patients also had elevated 4-hour radioactive iodine uptakes.

Renal transplant uptake of technetium-99m sulfur colloid in various time periods after transplantation.

The uptake of technetium-99m sulfur colloid (TSC) by transplanted kidneys undergoing rejection has been described. In this retrospective study, the value of TSC uptake in diagnosing renal rejection was studied in different time intervals after renal transplantation. Within 14 days after transplantation, increasing uptake was seen in 88% of 26 rejection episodes. In patients with acute tubular necrosis, 42% of their studies showed TSC uptake. TSC did not predict rejection within the three days prior to rejection. Sensitivity, specificity and accuracy of 128 TSC studies were compared at different thresholds of TSC uptake; at best, accuracy was only 76%. In later time intervals, a much smaller percentage of patients had increasing uptake with rejection; this tendency was to remain unchanged. Many non-rejection studies showed some TSC uptake. In chronic rejection, persistently marked uptake dominated prior to one year after transplantation, but not beyond this. Thus, within 14 days after transplantation, TSC uptake may support the diagnosis of rejection. Thereafter its value becomes greatly limited.