An atlas of renography with Tc-99m sestamibi: comparison with Tc-99m DTPA

Tc-99m sestamibil demonstrates considerable renal uptake followed by net urinary clearance similar to that of creatinine. The authors have previously shown that renograms could be obtained in cardiac patients by imaging during the rest injection of the perfusion agent. The present study shows correlating Tc-99m sestamibi and Tc-99m DTPA studies in hypertensive patients with a spectrum of findings, including aortic aneurysms, asymmetry due to renovascular disease, cysts, bilateral renal dysfunction, and horseshoe kidney. Tc-99m sestamibi images have persisting background activity in the liver and spleen, but show renal structure and function in adequate detail. Quantitative analysis confirms that Tc-99m sestamibi has higher renal uptake, but less excretion than Tc-99m DTPA. Review of these correlating studies suggests straightforward transfer of diagnostic expertise with standard renography to this new application.

The VEX-test for myocardial scintigraphy with thallium-201 and sestamibi: effect on abdominal background activity

High abdominal background activity of 99mTc-sestamibi may interfere with the diagnosis in studies in which a coronary vasodilator is used; supplemental dynamic exercise might reduce this problem.

METHODS

Clinical and angiographic determinants of subdiaphragmatic-to-myocardial activity ratios were measured on immediate poststress left anterior oblique images and on corresponding tomographic studies 1 hr after injection in 600 sestamibi studies. Similar measurements were made in 550 historic controls with planar 201Tl imaging. Patients performed symptom-limited ergometry when there were no limiting factors, dipyridamole-handgrip in which ergometry was not possible and VEX (vasodilator followed by symptom-limited ergometry) in which exercise capacity was reduced.

RESULTS

Abdominal activity was higher with sestamibi than with 201Tl, in women versus men, and with dipyridamole-based tests compared to exercise alone. Compared to the dipyridamole-handgrip, 3 min of ergometry as part of VEX decreased abdominal background (p < or = 0.02) by 18% on immediate 201Tl images, by 13% on immediate sestamibi images and by 12% on 1-hr delayed sestamibi tomoacquisitions.

CONCLUSIONS

Poststress abdominal background activity is influenced by similar factors with both agents. Supplemental exercise following dipyridamole reduces potentially interfering abdominal activity but perhaps not as efficiently with sestamibi as with 201Tl.

Dynamic renal imaging with technetium-99m-sestamibi in hypertension: potential for assessment of renovascular disorders

The myocardial perfusion agent, 99mTc-sestamibi (MIBI), offers the potential to combine renal and myocardial imaging because of high initial renal extraction and significant renal clearance.

METHODS

Dynamic renal imaging was performed during rest MIBI injections in 3 normal subjects (NS) and 91 patients referred for cardiac assessment. Ten served as normal controls, and 81 were hypertensive. Renal activity of MIBI during the first transit, uptake and excretory phases of the study was quantified. These data were compared with the normal kinetics of 99mTc-diethylenetriaminepentaacetic acid (DTPA) in concurrent studies.

RESULTS

With MIBI, clear definition of the kidneys was possible on all phases in most studies; occasionally, overlap with liver or spleen provided a minor problem. Renal MIBI activity reached levels 70% greater than DTPA during first transit and remained higher throughout the study; renal/background activity ratios were also higher on the MIBI study (p < 0.001). During the excretory phase with MIBI, hepatic and splenic activity did not decline, and gut activity increased. In NS, 40% of the total activity was excreted in the urine in 1 hr; urinary MIBI clearances approximated creatinine clearance. Asymmetry in initial renal uptake was seen in 14 of 81 hypertensive patients (17%); renal cysts and aortic dilatation could also be identified.

CONCLUSION

These data suggest that ancillary renography during rest injection of MIBI could be a useful addition to the cardiovascular assessment of selected patients.

The variability of processing of technetium-99m DTPA renography. Role of interpolative background subtraction

In quantitative renography, observer-dependent selection of renal outlines and background regions may account for considerable variability. This study of differential renal function with Tc-99m DTPA scintigraphy compares interpolative background subtraction with the authors' routine techniques; the latter involves background-subtracted uptake on data integrated over 1-3 minutes after injection. Other techniques considered were omission of background subtraction and use of 1-2 minute integration. The normal range was established in 24 hypertensive patients who had a normal angiogram and a normal radiometric glomerular filtration rate. The test set of 52 other hypertensive patients included 27 with renal artery stenosis. All techniques correlated well with the routine method (r > or = 0.98); however the interpolative background technique was unique in preserving the depiction of renal asymmetry but reducing the variability of replicate measurements (P < 0.05). Reduced renal function increased the variability of routine measurements, but the interpolative background subtraction method performed better in this instance (P < 0.01). Thus, the new technique appears to improve the definition of renal outlines and increase the reliability of measurements of differential renal function.

Chromium-51 labeling of sheep red blood cells

The failure of sheep red blood cells (RBCs) labeled with Chromium-51 (Cr-51) using the ascorbic acid technique to act as a suitable intravascular marker of blood volume in a septic sheep model prompted us to investigate the technique of radiolabeling sheep erythrocytes with this isotope. Consequently, we studied thirteen sheep in which the labeling efficiency of Cr-51 as sodium chromate and hemoglobin typing was determined for each animal. Mean Cr-51 labeling efficiency of sheep RBCs was 67.5% (n = 13). Although 5 of the 13 sheep were discovered to have two types of hemoglobin (Hb) as determined by electrophoresis, overall labeling efficiency of sheep RBCs was determined to be independent of the type of hemoglobin present. However, when two types of Hb were present (Hb-A and Hb-B), Cr-51 had a higher affinity for Hb-B (80%) than Hb-A (20%) even though both Hb types are present in similar proportions (Hb-A = 53%, Hb-B = 46%). The results of this study indicate that sheep RBCs express a lower labeling efficiency for Cr-51 than do human RBCs and that Cr-51 has a higher affinity for Hb-B than for Hb-A when both hemoglobin types are present. This difference is noteworthy when interpreting Cr-51 RBC data in experimental sheep models. Furthermore, caution should be exercised when extrapolating established human protocols to animal models.

Pulmonary thallium-201 uptake following dipyridamole-exercise combination compared with single modality stress testing

Angiographic and clinical determinants of pulmonary uptake of thallium-201 were assessed in a laboratory setting where supine bicycle exercise is used for stress testing in the absence of limiting pharmacologic or physical factors, and where symptom-limited exercise is added to intravenous dipyridamole infusion in other cases. Angiographic correlation was available in 400 patients, including 130 tested with exercise, 94 in whom only handgrip or abbreviated bicycle exercise could be used after dipyridamole, and 176 in whom intravenous dipyridamole was combined with a significant level of exercise. For each test mode, lung/myocardial ratios on the immediate image were highly correlated (p less than or equal to 0.001) with a score based on the number of critical coronary artery stenoses, with grading by contrast ventriculography, and with the number of stenosed (greater than or equal to 50%) arteries; relationships (p less than 0.05) to history of myocardial infarction and to gender were also present. Multiple regression analysis showed the critical stenosis score and ventricular dysfunction to be the only significant determinants. When dipyridamole based tests were compared with exercise, curves of receiver-operating characteristics showed a tendency to better diagnostic performance. When dipyridamole is incorporated in stress testing, the value of increased lung uptake as an ancillary diagnostic sign is similar to that established for exercise.

Metabolic response to exercise in malignant hyperthermia-sensitive patients measured by 31P magnetic resonance spectroscopy

The currently favored theory of pathogenesis of malignant hyperthermia (MH) implicates an abnormality in skeletal muscle calcium ion transport. During a MH crisis a profound lactic acidosis occurs and in MH-sensitive individuals a delayed recovery of venous lactate has been previously noted postexercise. We have used 31P magnetic resonance spectroscopy to follow noninvasively in vivo changes in muscle of intracellular pH and high-energy phosphate metabolites during rest, exercise, and recovery of MH-sensitive subjects. Eleven biopsy-positive MH-sensitive patients have been studied and compared to 26 normal subjects. The MH-sensitive subjects as a group prematurely dropped their intracellular pH during mild aerobic exercise and they demonstrated a marked delay before the recovery of pH after maximal exercise. PCr/(PCr + Pi) ratios also dropped early during exercise but recovered normally. The observed changes in pH and PCr/(PCr + Pi) are consistent with a myopathy in MH-susceptible individuals.