Comparative analysis of full-time, half-time, and quarter-time myocardial ECG-gated SPECT quantification in normal-weight and overweight patients.

BACKGROUND: The introduction of a camera-based dose-reduction strategy in myocardial perfusion imaging (MPI) clinical setting entails the definition of objective and reproducible criteria for establishing the amount of activity to be injected. AIM: The aim is to evaluate the impact of count statistics on the estimation of summed-scores (SS), end-diastolic volume (EDV), end-systolic volume (ESV), and ejection fraction (EF). METHODS: Data rest/stress ECG-gated SPECT (2-day protocol and 8 MBq·kg-1) were acquired with Bright View gamma camera and Astonish algorithm for 40 normal-weight and 40 overweight patients. Assuming that count statistics of shorter acquisition time may simulate that of lower injected activity, three simultaneous scans (full-time, half-time, and quarter-time scans) were started at the same time but with different acquisition time/projection (30, 15 and 8 seconds). RESULTS: A significant difference between SS values of half-time and quarter-time stress scans was found for overweight group (P = .006). Post hoc test showed significant differences for ESV (P < .05), EDV (P < .01) and EF (P < .05) between half-time and quarter-time scans for both patient groups. CONCLUSIONS: The reduction of the count-statistics to a quarter of the MPI reference influenced negatively the quantification in overweight patients. The decrease of radiopharmaceutical activity to 25% of the reference seems practicable for normal-weight patients, while it is more appropriate an activity reduction limited to 50% for overweight and obese patients.

Temporal evolution of administered activity in cardiac gated SPECT and patients' effective dose: analysis of an historical series.

PURPOSE: Myocardial perfusion imaging contributes >20 % of the average medical radiation exposure to the population in the USA. Imaging protocols able to achieve a radiation exposure ≤9 mSv in 50 % of the studies by 2014 have been recommended. The aim of this study was to analyse the temporal evolution of administered activities in patients scheduled for dual-day (99m)Tc tracer gated single photon emission computed tomography (SPECT) and to compare different dose administration protocols in terms of patients' effective dose. METHODS: Patients evaluated from 1 July 2002 to 31 January 2012 were allocated according to the protocol adopted: group 1: fixed activity according to diagnostic reference level: 740 MBq up to 80 kg (adapted for weight <60 kg); 900 MBq 80-100 kg, 1,110 MBq >100 kg, standard filtered back-projection (FBP) reconstruction; group 2: weight-adjusted activity: 8 MBq/kg up to 1,110 MBq, standard FBP reconstruction; and group 3: 4 MBq/kg, UltraSPECT wide beam reconstruction (WBR) reconstruction. A dual-head Anger camera (GE Helix) was used. RESULTS: A total of 9,060 patients were allocated to different groups: 4,751 in group 1, 2,844 in group 2 and 1,465 in group 3. The stress + rest administered activity was 1,617 ± 180 in group 1, 1,136 ± 260 in group 2 and 682 ± 164 MBq in group 3 (all p < 0.001). Patients' effective dose was 13.7 ± 3 in group 1, 9.5 ± 2.8 in group 2 and 5.7 ± 1.6 mSv in group 3 (all p < 0.001). The 50th percentile was 12.6 in group 1, 9.1 in group 2 and 5.3 mSv in group 3. The effective dose received by the dedicated cardiologists was 2.1, 1.5 and 1.0 µSv/exam in group 1, group 2 and group 3 periods, respectively (all p < 0.001). CONCLUSION: A significant reduction over time in the administered activity for gated SPECT was achieved; accordingly, a significant reduction in patients' exposure was obtained. A simple weight-adjusted strategy with 8 MBq/kg immediately fulfils the recommendations to limit exposure. In selected group 3 patients, a stress-only strategy allows for studies with <3 mSv exposure. Thus, at least the adoption of a new reconstruction algorithm is strongly encouraged, and suggested tracer activities for cardiac gated SPECT are to be revised.

Innovative reconstruction algorithms in cardiac SPECT scintigraphy.

The recent entry into the market of some advanced iterative reconstruction algorithms (IA) optimized for bone and cardiac studies has raised a great interest among specialists in nuclear medicine. In particular, myocardial perfusion studies have received a significant boost thanks to the superior quality of images obtained with these new reconstruction methods. Differently from the filtered back-projection (FBP), the basic principles of the iterative reconstruction techniques are less known; unclear is the way by which the iterative methods are able to include compensations for the main degradation phenomena in SPECT imaging. Aim of this review is to provide a simple introduction to the iterative solution of the tomographic problem by using its matricial representation. This paper will also provide simple graphical examples of how phenomena such as attenuation and depth dependent resolution can be modelled in the projection operator. The main degrading factors in cardiac SPECT images will be retrieved along with some indication of the effectiveness of the corrections adopted. This step makes clear the noteworthy qualitative improvement obtained with these advanced algorithms. A brief summary of the main features of the most widespread new iterative reconstruction algorithms will be presented. The majority of manufacturers emphasize the reduction of acquisition times allowed by these innovative algorithms. Finally, because of the awareness of the increasing exposure of the population due to the increasing number of imaging studies with ionizing radiation, the use of these advanced algorithms to achieve a simultaneous reduction in patient dose and acquisition time will be also shown.

Decreased [99mTc]Sestamibi uptake with dobutamine versus dipyridamole stress.

AIM: Animal studies suggest an interference of dobutamine on [99mTc]sestamibi uptake. In this study dobutamine was compared to dipyridamole rest-stress [99mTc]sestamibi uptake ratio (UR). METHODS: Twenty-five patients with suspect coronary artery disease (CAD) underwent rest, dobutamine, and dipyridamole [99mTc]sestamibi SPECT at 24-h intervals and coronary angiography. UR was calculated separately for each coronary territory considering injected dose and acquisition delay. RESULTS: There were 38 CAD territories in 20 patients. On a patient basis, dipyridamole SPECT sensitivity was 85%, versus 70% for dobutamine. On a territory basis, sensitivity was 66% versus 42% (P<0.05), and specificity 92% versus 86%, respectively for dipyridamole versus dobutamine. In the 38 CAD territories, dipyridamole UR was -4.1+/-29.4%, and dobutamine UR was -13.1+/-19.9% (P<0.05). In the 37 no-CAD territories, UR was 34+/-23.6% for dipyridamole and -0.4+/-17.8% for dobutamine (P<0.0001). UR difference between CAD versus no-CAD territories was larger using dipyridamole (P<0.0001) than dobutamine (P<0.005). CONCLUSIONS: The UR comparison confirms that [99mTc]sestamibi uptake underestimates the blood flow heterogeneity induced by dobutamine more than that produced by dipyridamole.

ECG-manifest and ECG-silent dipyridamole technetium-99m sestamibi SPET perfusion defects in patients with ischaemic heart disease.

At dipyridamole myocardial scintigraphy, perfusion defects are seldom backed up by significant ECG changes. This would suggest myocardial blood flow heterogeneity, rather than true ischaemia, as the cause of the scintigraphic abnormalities. Electrocardiographic surface mapping has been documented to be more accurate than standard 12-lead ECG in the detection of provoked ischaemia. Thus, to investigate the relationship between ECG changes and perfusion abnormalities, body surface maps were recorded during dipyridamole infusion in 55 subjects (11 normals and 44 patients with ischaemic heart disease) undergoing dipyridamole technetium-99m sestamibi single-photon emission tomography (SPET). All had a normal resting ECG. The extent and severity of the sestamibi defect were quantified. New negative areas in the isointegral maps and rest-dipyridamole map differences >2 SD from normal limits were considered abnormal. After dipyridamole in normals, neither perfusion defects nor >/=1 mm ST segment depression on 12-lead ECG nor new negative areas in isointegral maps occurred. In patients, dipyridamole induced new perfusion defects in 35 (80%) but ST segment depression in only 18 (41%, P<0.001). Of the 35 patients with perfusion defects, 17 (49%, group 1) showed ST segment depression, while the other 18 (51%, group 2) did not. Abnormal body surface maps were found in 100% of group 1 and 88% of group 2 patients (NS). In group 1, the provoked hypoperfusion was of greater extent (P=0.007) and severity (P=0.01) and the onset of map abnormalities was significantly earlier (P<0. 001) than in group 2; time to map abnormalities was also significantly shorter than time to ST segment depression (P=0.01). In the 35 patients with complete scintigraphic, body map and angiographic data, the severity of reversible perfusion defect proved to be the strongest correlate of ST segment depression upon logistic regression analysis. Thus, sestamibi SPET abnormalities after dipyridamole are almost always associated with electrical changes on body surface maps, suggesting myocardial ischaemia as their cause. The much less common 12-lead ECG changes are slower to appear and reflect a more severe hypoperfusion.

Technetium-99m-sestamibi SPECT to detect restenosis after successful percutaneous coronary angioplasty.

UNLABELLED: This study evaluated the accuracy of 99mTc SPECT in predicting restenosis after primary successful PTCA. METHODS: Thirty-seven patients with equivocal symptom-limited exercise stress testing were evaluated. All patients underwent separate day exercise-rest 99mTc-sestamibi SPECT. The perfusion studies were evaluated using three different methods of analysis: visual inspection, semiquantitative and quantitative polar map analysis. The perfusion studies were interpreted in absence of a pre-PTCA scan. All patients underwent a control coronary angiography within 1 mo. RESULTS: Sensitivity and specificity of 99mTc-sestamibi SPECT in predicting restenosis were 87.5-78%, 50-65% and 75-74% for visual inspection, semiquantitative and quantitative polar map analysis, respectively. Sensitivity and specificity related to the vascular territories were: LAD territory 93-73% (qualitative analysis), 53-60% (semiquantitative analysis), 80-67% (quantitative analysis); LCX territory 83-100% (qualitative analysis); and 33-100% (semiquantitative analysis), 67-100% (quantitative analysis); and RCA territory 67-80% (qualitative analysis), 67-60% (semiquantitative analysis), 67-80% (quantitative analysis). CONCLUSION: These data suggest that 99mTc-sestamibi SPECT is a useful noninvasive tool in the follow-up evaluation of patients who have undergone angiographically successful coronary angioplasty even in the absence of a pre-PTCA perfusion study.

Influence of the assessment of defect severity and intravenous nitrate administration during tracer injection on the detection of viable hibernating myocardium with data-based quantitative technetium 99m-labeled sestamibi single-photon emission computed tomography.

BACKGROUND: This study aimed to verify whether the assessment of defect severity and the infusion of nitrates during tracer injection improve the capability of data-based 99mTc-labeled sestamibi single-photon emission computed tomography (SPECT) to recognize hibernating myocardium. METHODS AND RESULTS: Of 66 asynergic coronary territories in 40 patients with left ventricular dysfunction, 28 had postrevascularization functional recovery (hibernating) and 38 had unchanged dysfunction (fibrotic). Defect severity was lower in the hibernating than in the fibrotic territories on both baseline (p < 0.01) and nitrate SPECT (p < 0.002). Nitrate was superior to baseline SPECT to differentiate the hibernating from the fibrotic territories (sensitivity 96% vs 75%, p < 0.05; receiver-operating characteristic curve area 0.75 vs 0.63, p < 0.001) and to identify the patients with improved left ventricular ejection fraction (receiver-operating characteristic curve area 0.68 vs 0.58; p < 0.05). CONCLUSIONS: The analysis of defect severity in combination with nitrate infusion clearly improves the value of 99mTc-labeled sestamibi SPECT for the recognition of hibernating myocardium and the prediction of postrevascularization recovery.

Technetium-99m sestamibi tomographic evaluation of residual ischemia after anterior myocardial infarction.

OBJECTIVES: This study investigated the value of sestamibi scintigraphy in assessing residual ischemia after anterior myocardial infarction. BACKGROUND: Serial imaging with sestamibi, the uptake and retention of which correlate with regional myocardial blood flow and viability, has been used to estimate salvaged myocardium and risk area after acute infarction. We recently documented that recovery of perfusion and contraction in the infarcted area may continue well after the subacute phase, suggesting myocardial hibernation. Some underestimation of viability in the setting of hibernating myocardium by sestamibi imaging has been reported. METHODS: We studied 58 patients in stable condition after Q wave anterior infarction. Regional perfusion and function were quantitatively assessed by sestamibi tomography and two-dimensional echocardiography at 4 to 6 weeks and at 7 months after infarction. In sestamibi polar maps, abnormal areas with tracer uptake > 2.5 SD below our reference values were computed at rest and after symptom-limited exercise. On two-dimensional echocardiography the ejection fraction and extent of rest wall motion abnormalities were assessed by a computerized system. All patients had coronary angiography between the two studies. RESULTS: At 7 months the extent of rest sestamibi defect was significantly reduced in 40 patients (69%, group 1) and unchanged in 18 (31%, group 2). Rest wall motion abnormalities and ventricular ejection fraction significantly improved in group 1 but not in group 2. Underlying coronary disease, patency of the infarct-related vessel and rest sestamibi defect extent at 5 weeks were comparable between the two groups. At 7 months, an increase in the reversible (stress-rest defect) tracer defect was observed in group 1 (p < 0.05) despite a smaller stress-induced hypoperfusion (p < 0.05). Reversible sestamibi defects and stress hypoperfusion were unchanged in group 2. In 38 (95%) of 40 group 1 patients, the area showing reversible sestamibi defects at 7 months matched the area showing fixed hypoperfusion at 5 weeks. CONCLUSIONS: The reduction in the rest tracer uptake defect that can occur late after infarction may affect the assessment of ischemic burden by sestamibi imaging early after anterior myocardial infarction.

Evaluation of technetium-99m-sestamibi lung uptake: correlation with left ventricular function.

UNLABELLED: Lung uptake of 201Tl is a reliable marker of left ventricular dysfunction. The goal of our study was to establish whether the evaluation of lung-to-heart uptake ratios (LHR) with 99mTc-sestamibi imaging may provide valuable information. METHODS: We studied 72 male subjects with recent anterior myocardial infarction undergoing 99mTc-sestamibi first-pass ventriculography and SPECT perfusion imaging. A group of 46 gender-matched subjects with low pre-test likelihood of CAD and normal exercise and rest 99mTc-sestamibi perfusion images was used as a control. The lung-to-heart count ratios (LHR) were calculated on planar projections from the sets of SPECT images. RESULTS: Both groups were studied at rest and after a symptom-limited exercise tolerance test. In the control group a significant decrease in LHR was observed during stress (p < 0.001). The infarcted group showed significantly higher LHR values both at rest and at stress. Exercise and rest LHR values did not differ significantly. A positive correlation was observed between LHR values and left ventricular ejection fraction at rest and stress. CONCLUSION: LHR, measured by 99mTc-sestamibi imaging, gives clinically useful information. Both resting and postexercise values are correlated with ejection fraction and should predict left ventricular dysfunction.

[Importance of late reversibility in the identification of myocardial viability at risk after myocardial infarction]. / Importanza della reversibilità tardiva nell'identificazione del miocardio vitale a rischio in esiti di infarto miocardico.

The prevalence of late reversibility in single photon emission computed tomography (SPECT) thallium 201 stress/redistribution studies is still controversial. The aim of our work was to evaluate the prevalence of late reversibility at infarct site in an unselected population of patients with previous acute myocardial infarction (AMI). We studied by SPECT thallium 201 and pharmacologic stress with dipyridamole (DIP) as well as by two-dimensional echocardiography 58 consecutive patients with previous AMI (50 men of mean age 57 years, range 40-73; 8 women of mean age 58 years, range 50-68). All the patients with perfusion defect at infarct site that was persistent at 4-hour study, were reimaged after 24 hours. Twenty-one (36%) of 58 patients complained about postinfarction angina. Following intravenous DIP (0.56 mg/kg), heart rate increased from 67 +/- 14 to 83 +/- 14 b/min (< 0.0001) and diastolic and systolic arterial pressures dropped from 86 +/- 12 and 139 +/- 25 mmHg to 79 +/- 14 and 132 +/- 27 mmHg, respectively (< 0.0001; < 0.0005). Of 57 patients with stress perfusion defects at infarct site, 16 (28%) demonstrated reversibility after 4 hours and 19 (33.4%) after 24 hours, with a total of 35 (61.4%) patients demonstrating reversibility by combined 4-hour and 24-hour imaging (< 0.0001 versus reversibility at 4-hour imaging alone). Thus, of 41 patients with 4-hour persistent thallium defects at infarct site, 19 (46.3%) demonstrated late reversibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Biventricular function in Friedreich's ataxia: a radionuclide angiographic study.

The systolic and diastolic function of both ventricles was assessed by radionuclide angiography in 21 patients with Friedreich's ataxia and hypertrophic cardiomyopathy. The indices of systolic function of the two ventricles and those of diastolic function of the right ventricle were generally normal. But in patients with Friedreich's ataxia the time to peak filling rate divided by the diastolic time of the left ventricle was significantly larger than normal. The increase correlated with the heart rate (r = 0.79) and this suggests an alteration in the timing of ventricle filling that is more evident at high heart rates. Movement of the left ventricle was little impaired; however, in 48% of the patients with Friedreich's ataxia the right ventricle showed evidence of hypokinetic segments. Because there is a tendency for congestive heart failure to develop in patients with Friedreich's ataxia, this hypokinesis of the right ventricle should be monitored at follow up.

Computerized analysis of equilibrium radionuclide ventriculography time-activity curve in the assessment of left ventricular performance: comparison of two methods.

Two methods for the analysis of left ventricle time-activity curve (TAC) of equilibrium gated ventriculography were compared in three groups of subjects [8 controls, 13 patients with coronary artery disease (CAD), 11 patients with myocardial infarction (MI). The first method was based on third-degree polynomial fitting, the second on Fourier analysis. The following parameters were calculated: peak ejection rate (PER), peak filling rate (PFR), time to PER and PFR, and filling fraction at the first third of diastole. A preliminary study of changing values of PER and PFR and of the mean error with increasing number of harmonics summed in order to obtain the best fitting of TAC demonstrated that beyond the sum of the first four harmonics there was no further significant improvement. The advantages of Fourier analysis are as follows: it is independent of the operator and fits only one function to the whole cardiac cycle; it requires less computer time; it provides better differentiation between controls and CAD patients. All of the 13 CAD patients had abnormal PFR on Fourier analysis, only 9 on polynomial analysis. At rest, 9 of the CAD patients had wall motion abnormalities, while only two had an abnormal ejection fraction.