Influence of the different biokinetics of sestamibi and tetrofosmin on the interpretation of myocardial perfusion imaging in daily practice.

AIM: Digestive activity can interfere with the interpretation of myocardial perfusion single photon emission computed tomography using sestamibi or tetrofosmin. Compared with sestamibi, the liver clearance of tetrofosmin is more rapid, but its absolute cardiac uptake is lower. In this study, the activity of sestamibi and tetrofosmin was quantified after exercise or pharmacological stress and at rest to objectify the biokinetic differences and to evaluate whether there is a correlation between quantitative measurements and the visual assessment of image quality. METHODS: Left ventricular activity and five ratios (R1-R5) of cardiac to adjacent extra-cardiac activity were quantified in 204 sestamibi (68 exercise stress/56 pharmacological stress/80 rest) and 221 tetrofosmin (67 exercise stress/59 pharmacological stress/95 rest) studies. Image quality was assessed by a three-point score (1, good; 2, moderate; 3, poor) and correlated with the heart to left supra-diaphragmatic region (R1) and heart to right supra-diaphragmatic region (R2) ratios. RESULTS: The mean left ventricular activity was higher for sestamibi, especially at rest (sestamibi, 0.21+/-0.05 counts/pixel/injected MBq; tetrofosmin, 0.16+/-0.042 counts/pixel/injected MBq; P<0.001). By contrast, most ratios were higher with tetrofosmin, particularly for the exercise stress and rest studies. Using the three-point quality scoring, more sestamibi than tetrofosmin studies were scored as 3 (12.2% versus 6.3%), also particularly for the exercise stress and rest studies. A highly significant relationship was found between decreasing R1 and R2 and an increasing quality score, regardless of the radiopharmaceutical used (P values between 0.02 and <0.001). CONCLUSIONS: Despite a lower cardiac uptake, the more rapid liver clearance of tetrofosmin than sestamibi significantly improves the ratios of cardiac to digestive activity, especially after exercise or at rest. These quantitative differences in biokinetics result in less poor scans with tetrofosmin in daily practice.

Head-to-head comparison of uncorrected and scatter corrected, summed and end diastolic myocardial perfusion SPECT in coronary artery disease.

OBJECTIVES: Compared with other non-invasive methods for diagnosing coronary artery disease (CAD), myocardial perfusion imaging (MPI) suffers from some lack of specificity, especially in patients with a small heart. Allowing the assessment of perfusion on end diastolic images instead of summed images, gated single photon emission computed tomography (SPECT) constitutes an attractive method for increasing the accuracy of MPI. Scatter correction, known to improve image contrast, might also be interesting. The present study aimed at comparing scatter corrected to uncorrected gated MPI for CAD diagnosis. METHODS: The results for 100 patients referred for gated 99mTc sestamibi SPECT were analysed. They were divided into two subgroups according to their end systolic volume (ESV) measured by QGS analysis (group A, ESV > or =30 ml, n=65; group B, ESV <30 ml, n=35). For each patient, a total defect score (TDS) was quantified on four polar maps (uncorrected and scatter corrected, summed, and uncorrected and scatter corrected, end diastolic). The optimal TDS separating non-CAD from CAD patients was calculated by analysis of the receiver operating characteristic (ROC) curve for the four data sets, using the coronary angiogram as a 'gold standard'. RESULTS: In the whole patient population, the accuracy of the uncorrected data was 67% for the end diastolic images and 71% for the summed images (sensitivity, 66% and 70%; specificity, 71% and 79%, respectively). After scatter correction, the accuracy did not change for the end diastolic data (accuracy, 67%; sensitivity, 63%; specificity, 93%) and increased to 74% for the summed data (sensitivity, 73%; specificity, 79%). In group A, the uncorrected data were 72% accurate for the end diastolic images and 78% for the summed images (sensitivity, 72% and 79%; specificity, 75% and 75%, respectively). After correction, the accuracy of end diastolic images increased to 77% (sensitivity, 77%; specificity, 75%), and did not change for the summed images (accuracy, 78%; sensitivity, 79%; specificity, 75%). In group B, the accuracy of uncorrected images amounted to 51% for both end diastolic and summed data (sensitivity, 48% and 40%; specificity, 60% and 80%, respectively). After correction, it increased to 57% for the end diastolic images and to 63% for the summed images (sensitivity, 48% and 64%; specificity, 80% and 60%, respectively). CONCLUSIONS: Despite lower blurring on end diastolic compared with summed images, non-scatter corrected end diastolic data were least accurate for the diagnosis of coronary artery disease in patients with a high prevalence of disease. Scatter correction, by improving the delineation of perfusion defects, increased the accuracy of quantitative MPI for the diagnosis of CAD in a large number of patients, more particularly in those with a small heart.

FP-CIT SPECT in clinically inconclusive Parkinsonian syndrome during amiodarone treatment: a study with follow-up.

OBJECTIVES: To evaluate whether dopamine transport system imaging by FP-CIT single-photon emission computed tomography (SPECT) can be helpful to differentiate idiopathic Parkinson's disease (IPD) from secondary Parkinsonism induced by amiodarone. METHODS: Twenty-two patients with Parkinsonism during amiodarone therapy were evaluated by clinical neurological examination and FP-CIT SPECT. Thereafter, amiodarone was discontinued whenever possible and antiparkinsonian treatment was modified, if required. Clinical neurological status was reevaluated within a year of the SPECT examination. RESULTS: At baseline, clinical neurological examination was quite similar in all patients. No clinical symptom was able to clearly orientate the diagnosis toward IPD or drug-induced Parkinsonism. Using SPECT, the number of normal and abnormal patients was evenly distributed. In the abnormal SPECT group, amiodarone was modified in seven patients of whom six improved at follow-up. Antiparkinsonian treatment had been modified in all the patients. In the four cases with no amiodarone changes, clinical improvement was noted if antiparkinsonian treatment was optimized (three patients). In the 11 normal SPECT patients, amiodarone was modified in five patients. All patients ameliorated (two) or even normalized (three). In the six patients with normal SPECT in whom amiodarone had not been modified, symptoms remained stable despite the absence of antiparkinsonian treatment. CONCLUSION: In patients treated with amiodarone, IPD is sometimes clinically difficult to differentiate from drug-induced Parkinsonism. Using FP-CIT, a normal scan suggests drug-induced Parkinsonism, hence, there is no need for antiparkinsonian treatment and all possible attempts to reduce or preferably stop amiodarone. An abnormal scan, on the other hand, indicates IPD. In this case, treating IPD seems to have more impact on motor changes than modifying the antiarrhythmic drug.

Variability of left ventricular ejection fraction and volumes with quantitative gated SPECT: influence of algorithm, pixel size and reconstruction parameters in small and normal-sized hearts.

PURPOSE: Several software packages are commercially available for quantification of left ventricular ejection fraction (LVEF) and volumes from myocardial gated single-photon emission computed tomography (SPECT), all of which display a high reproducibility. However, their accuracy has been questioned in patients with a small heart. This study aimed to evaluate the performances of different software and the influence of modifications in acquisition or reconstruction parameters on LVEF and volume measurements, depending on the heart size. METHODS: In 31 patients referred for gated SPECT, 64(2) and 128(2) matrix acquisitions were consecutively obtained. After reconstruction by filtered back-projection (Butterworth, 0.4, 0.5 or 0.6 cycles/cm cut-off, order 6), LVEF and volumes were computed with different software [three versions of Quantitative Gated SPECT (QGS), the Emory Cardiac Toolbox (ECT) and the Stanford University (SU-Segami) Medical School algorithm] and processing workstations. Depending upon their end-systolic volume (ESV), patients were classified into two groups: group I (ESV>30 ml, n=14) and group II (ESV<30 ml, n=17). Agreement between the different software packages and the influence of matrix size and sharpness of the filter on LVEF and volumes were evaluated in both groups. RESULTS: In group I, the correlation coefficients between the different methods ranged from 0.82 to 0.94 except for SU-Segami (r=0.77), and were slightly lower for volumes than for LVEF. Mean differences between the methods were not significant, except for ECT, with which LVEF values were systematically higher by more than 10%. Changes in matrix size had no significant influence on LVEF or volumes. On the other hand, a sharper filter was associated with significantly larger volume values though this did not usually result in significant changes in LVEF. In group II, many patients had an LVEF in the higher range. The correlation coefficients between the different methods ranged between 0.80 and 0.96 except for SU-Segami (r=0.49), and were slightly worse for volumes than for LVEF values. In contrast to group I, however, inter-method variability was quite large and most mean LVEF differences were significant. LVEF was systematically highest with ECT and lowest with SU-Segami. With QGS, changes in matrix size from 64(2) to 128(2) were associated with significantly larger volumes as well as lower LVEF values. Increasing the filter cut-off frequency had the same effect. With SU-Segami, a larger matrix was associated with larger end-diastolic volumes and smaller ESVs, resulting in a highly significant increase in LVEF. Increasing the filter sharpness, on the other hand, had no influence on LVEF though the measured volumes were significantly larger. CONCLUSION: In patients with a normal-sized heart, LVEF and volume estimates computed from different commercially available software packages for quantitative gated SPECT are well correlated. LVEF and volumes are only slightly sensitive to changes in matrix size. Smoothing, by contrast, is associated with significant changes in volumes but usually not in LVEF values. However, owing to the specific characteristics of each algorithm, software should not be interchanged for follow-up in an individual patient. In small hearts, on the other hand, both the used software and the matrix size or smoothing significantly influence the results of quantitative gated SPECT. LVEF values in the higher range are frequently observed with all the studied software except for SU-Segami. A larger matrix or a sharper filter could be suggested to enhance the accuracy of most commercial software, more particularly in patients with a small heart.