Validation of a model of left ventricular segmentation for interpretation of SPET myocardial perfusion images.

Several models of left ventricular segmentation have been developed that assume a standard coronary artery distribution, and are currently used for interpretation of single-photon emission tomography (SPET) myocardial perfusion imaging. This approach has the potential for incorrect assignment of myocardial segments to vascular territories, possibly over- or underestimating the number of vessels with significant coronary artery disease (CAD). We therefore sought to validate a 17-segment model of myocardial perfusion by comparing the predefined coronary territory assignment with the actual angiographically derived coronary distribution. We examined 135 patients who underwent both coronary angiography and stress SPET imaging within 30 days. Individualized coronary distribution was determined by review of the coronary angiograms and used to identify the coronary artery supplying each of the 17 myocardial segments of the model. The actual coronary distribution was used to assess the accuracy of the assumed coronary distribution of the model. The sensitivities and specificities of stress SPET for detection of CAD in individual coronary arteries and the classification regarding perceived number of diseased coronary arteries were also compared between the two coronary distributions (actual and assumed). The assumed coronary distribution corresponded to the actual coronary anatomy in all but one segment (#3). The majority of patients (80%) had 14 or more concordant segments. Sensitivities and specificities of stress SPET for detection of CAD in the coronary territories were similar, with the exception of the RCA territory, for which specificity for detection of CAD was better for the angiographically derived coronary artery distribution than for the model. There was 95% agreement between assumed and angiographically derived coronary distributions in classification to single- versus multi-vessel CAD. Reassignment of a single segment (segment #3) from the LCX to the LAD territory further improved the model's fit with the anatomic data. It is concluded that left ventricular segmentation using a model with assumed coronary artery distribution is valid for interpretation of SPET myocardial perfusion imaging.     

Proportional anatomical stereotactic atlas for visual interpretation of brain SPET perfusion images

A semi-automatic method was developed to determine the anterior (AC) and posterior (PC) commissures on brain single-photon emission tomographic (SPET) perfusion images, and then to draw the proportional anatomical Talairach's grid on each axial SPET image. First, the AC-PC line was defined on SPET images from the linear regression of four internal landmarks (frontal pole of the brain, inferior limit of the anterior corpus callosum, sub-thalamic point and occipital pole). Second, the SPET position of AC and PC points on the AC-PC line was automatically determined from measurements made on hard copies of magnetic resonance (MR) images of the patients. Finally, a proportional Talairach's grid was automatically drawn on each axial SPET image. To assess the accuracy of localization of AC and PC points, co-registered technetium-99m hexamethylpropylene amine oxime SPET and MR images from 11 subjects were used. The mean displacements between estimated points on SPET and true points on MRI (x=sagittal, y=frontal and z=axial displacement) were calculated. The mean displacements (in mm) were x=–1.4±1.8, y=–1.7±3.3 and z=–1.1±2.5 for AC, and x=–1.8±1.8, y=0.3±3.2 and =–1.3±2.7 for PC. These displacements represented an error of less than 5 mm at the anterior or posterior pole of the brain or at the vertex. Intra- and inter-observer comparisons did not reveal significant differences in mean displacements. Thus, this semi-automatic method results in reproducible and accurate stereotactic localization of SPET perfusion abnormalities. This method can be used routinely for repeat follow-up studies in the same subject as well as in different individuals without requiring SPET MRI co-registration.     

Effect of variable left ventricular vertical orientation on planar myocardial perfusion images

Differences in vertical orientation of the left ventricle within the chest cavity cannot be corrected by gamma camera positioning. The effect of variations in vertical angulation on the appearance of the diagnostically important left anterior oblique (LAO) view has not been previously evaluated. In the current study, a computer simulation of a normal left ventricle was created and "imaged," varying only the degree of vertical rotation. The effect of six vertical positions on the LAO image was assessed visually and with horizontal and circumferential profile analysis. Results indicate a homogenous distribution of counts in the horizontal views. With increasing verticality, there are fewer counts in the valve plane, while the inferoapex initially increases in count density, and then progressively decreases. Quantification revealed count variations of up to 37% in the valve plane and 45% in the inferoapex due entirely to differences in vertical orientation of the left ventricular simulation. A survey of 167 patients who underwent routine stress thallium imaging showed a vertical angulation that varied from 7 degrees to 64 degrees (mean = 37 degrees) as determined from the anterior view. Clinical images were similar in appearance to computer generated images after correction for anterior view foreshortening. The present study suggests that the accuracy of current quantitative thallium methods to detect coronary artery disease might be enhanced by the use of a revised set of normal standards corrected for vertical orientation of the left ventricle.     

Comparative value of ECG-gated blood pool SPET and ECG-gated myocardial perfusion SPET in the assessment of global systolic left ventricular function

Both electrocardiographically (ECG) gated blood pool SPET (GBPS) and ECG-gated myocardial perfusion SPET (GSPET) are currently used for the measurement of global systolic left ventricular (LV) function. In this study, we aimed to compare the value of GSPET and GBPS for this purpose. The population included 65 patients who underwent rest thallium-201 GSPET imaging at 15 min after (201)Tl injection followed by planar (planar(RNA)) and GBPS equilibrium radionuclide angiography immediately after 4-h redistribution myocardial perfusion SPET imaging. Thirty-five patients also underwent LV conventional contrast angiography (X-rays). LV ejection fraction (EF) and LV volume [end-diastolic (EDV) and end-systolic (ESV) volumes] were calculated with GBPS and GSPET and compared with the gold standard methods (planar(RNA) LVEF and X-ray based calculation of LV volume). For both LVEF and LV volume, the inter-observer variability was lower with GBPS than with GSPET. GBPS LVEF was higher than planar(RNA) (P<0.01) and GSPET LVEF (P<0.01). Planar(RNA) LVEF showed a slightly better correlation with GBPS LVEF than with GSPET LVEF: r=0.87 and r=0.83 respectively. GSPET LV volume was lower than that obtained using X-rays and GBPS (P<0.01 for both). LV volume calculated using X-rays showed a slightly better correlation with GBPS LV volume than with GSPET LV volume: r=0.88 and r=0.83 respectively. On stepwise regression analysis, the accuracy of GSPET for the measurement of LVEF and LV volume was correlated with a number of factors, including planar(RNA) LVEF, signal to noise ratio, LV volume calculated using X-rays, summed rest score and acquisition scan distance (i.e. the radius of rotation). The accuracy of GBPS for the measurement of LVEF and LV volume was correlated only with the signal level, the signal to noise ratio and the acquisition scan distance. Both GSPET and GBPS provide reliable estimation of global systolic LV function. The better reliability of GBPS and in particular its lower sensitivity to different variables as compared with GSPET favours its use when precise assessment of global systolic LV function is clinically indicated.     

A comparison and validation of blood-pool imaging and ECG-gated SPET myocardial perfusion imaging to assess left ventricular ejection fraction

The aim of this study was to validate the accuracy of left ventricular ejection fraction (LVEF) obtained by quantitative gated single photon emission tomography (QGS) perfusion imaging in comparison with gated blood-pool imaging. Resting gated myocardial perfusion imaging was performed in 269 patients with suspected or known coronary artery disease, and followed by equilibrium nuclear cardiac blood-pool imaging in one week. The later was considered as the reference standard. The LVEF from both methods were analyzed. The LVEF were calculated with QGS using Cedars Cardiac Quantification software. We found that LVEF from QGS and blood-pool (Bp)-LVEF were highly correlated (r=0.819, <0.001). Taken into consideration that QGS-LVEF was significantly different from Bp-LVEF (mean ± SD: 57.77% ± 19.28% vs 54.23% ± 15.41%, P<0.05), data were further analyzed by grouping participants based on end-systolic ventricular volume (ESV). QGS-LVEF was not significantly different from Bp-LVEF in the group where that ESV was larger than 15m, (mean ± SD: 52.71% ± 16.11% vs 51.83% ± 15.33%, P>0.05), whereas when ESV was smaller than 15 mL, QGS-LVEF was significantly higher than Bp-LVEF (mean ± SD: 80.53% ± 7.01%vs 65.06% ± 10.37%, P<0.05). Our findings demonstrate that when ESV values are larger than 15 mL, QGS- LVEF could replace Bp-LVEF. However, when ESV value is smaller than 15 mL, LVEF should be assessed in combination with blood-pool imaging.     

Assessment of left ventricular diastolic function from quantitative electrocardiographic-gated 99mTc-tetrofosmin myocardial SPET

We have developed new software which can evaluate left ventricular (LV) diastolic functional parameters from a quantitative gated SPET (QGS) program. To examine its accuracy, we compared these findings with the LV diastolic functional indices obtained from gated radionuclide ventriculography (RNV). Twenty-four patients were selected for this study. Gated SPET with technetium-99m tetrofosmin was performed and the QGS program was used with a temporal resolution of 32 frames per R-R interval. The LV volume of each frame was calculated and four harmonics of Fourier series were retained for the analysis of the LV volume curve. From this fitted curve and its first derivative curve, we derived LV systolic functional indices, e.g. ejection fraction (EF), peak ejection rate (PER) and time to PER (TPER), as well as LV diastolic functional variables, e.g. 1/3 filling fraction (1/3 FF), peak filling rate (PFR) and time to PFR (TPFR). Within 5+/-2 days, gated RNV was performed and diastolic functional parameters were determined by the same method. No significant difference was observed between the variables calculated by gated SPET and by gated RNV. There was a good correlation between EF, PER, TPER, 1/3 FF, PFR and TPFR determined by these two methods (EF: r=0.95, P<0.0001; PER: r=0.87, P<0.0001; TPER: r=0.84, P<0.0001; 1/3 FF: r=0.87, P<0.0001; PFR: r=0.92, P<0.0001; TPFR: r=0.89, P<0.0001). Bland-Altman plots did not reveal any significant degree of directional measurement bias in any of the comparisons of gated SPET data and RNV data. It is concluded that, in addition to the conventional LV systolic functional indices, our program accurately provides LV diastolic functional parameters from gated SPET. Also, this program will be useful for detecting LV diastolic dysfunction in various cardiac diseases before LV systolic dysfunction becomes evident.     

Effect of beta-blockade on low-dose dobutamine-induced changes in left ventricular function in healthy volunteers: assessment by gated SPET myocardial perfusion scintigraphy

Viability studies are often performed in patients receiving beta-blocking agents. However, the intake of beta-blocking agents could influence the identification of viable myocardium when low-dose dobutamine is used to demonstrate inotropic reserve. The aim of this study was to quantify the effect of beta-blockade on global and regional left ventricular function in healthy volunteers using low-dose dobutamine gated single-photon emission tomographic (SPET) myocardial perfusion scintigraphy. Ten subjects were studied once ”on” and once ”off” beta-blocker therapy (metoprolol succinate, 100 mg day^–1). On each occasion four consecutive gated SPET acquisitions (of 7 min duration) were recorded after injection of 925 MBq technetium-99m tetrofosmin on a triple-headed camera equipped with focussing (Cardiofocal) collimators. Acquisitions were made at rest (baseline 1 and 2) and 5 min after the beginning of the infusion of 5 and 10 μg kg^–1 min^–1 dobutamine. Wall thickening (WT) was quantified using a method based on circumferential profile analysis. Left ventricular ejection fraction (LVEF) was obtained using the Cedars-Sinai algorithm. Blood pressure (BP) and heart rate (HR) were recorded at the end of each acquisition. At baseline LVEF, WT and systolic BP values under beta-blockade were not significantly different from those obtained in the non-beta-blocked state. The mean HR and diastolic BP at baseline were lower under beta-blockade. Dobutamine administration (at 5 and 10 μg kg^–1 min^–1) induced a significant increase in WT, LVEF and systolic BP in all subjects both on and off beta-blockade. The increases in WT, LVEF and systolic BP in the beta-blocked state were less pronounced but not significantly different. HR increased significantly at 10 μg kg^–1 min^–1 dobutamine without beta-blocker administration, while no increase in HR was observed in the beta-blocked state. Beta-blocker therapy in healthy subjects attenuates the inotropic and chronotropic myocardial response to low-dose dobutamine. At doses of 5 and 10 μg kg^–1 min^–1 dobutamine, however, significant increases in global and regional left ventricular function can still be measured using consecutive gated SPET myocardial perfusion scintigraphy acquisitions even under beta-blocker therapy. Received 4 September and in revised form 3 November 1999     

SPECT myocardial perfusion imaging for the assessment of left ventricular mechanical dyssynchrony

Phase analysis of gated single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is an evolving technique for measuring LV mechanical dyssynchrony. Since its inception in 2005, it has undergone considerable technical development and clinical evaluation. This article reviews the background, the technical and clinical characteristics, and evolving clinical applications of phase analysis of gated SPECT MPI in patients requiring cardiac resynchronization therapy or implantable cardioverter defibrillator therapy and in assessing LV diastolic dyssynchrony.     

Effect of beta-blockade on low-dose dobutamine-induced changes in left ventricular function in healthy volunteers: assessment by gated SPET myocardial perfusion scintigraphy

Viability studies are often performed in patients receiving beta-blocking agents. However, the intake of beta-blocking agents could influence the identification of viable myocardium when low-dose dobutamine is used to demonstrate inotropic reserve. The aim of this study was to quantify the effect of beta-blockade on global and regional left ventricular function in healthy volunteers using low-dose dobutamine gated single-photon emission tomographic (SPET) myocardial perfusion scintigraphy. Ten subjects were studied once "on" and once "off" beta-blocker therapy (metoprolol succinate, 100 mg day(-1)). On each occasion four consecutive gated SPET acquisitions (of 7 min duration) were recorded after injection of 925 MBq technetium-99m tetrofosmin on a triple-headed camera equipped with focussing (Cardiofocal) collimators. Acquisitions were made at rest (baseline 1 and 2) and 5 min after the beginning of the infusion of 5 and 10 microg kg(-1) min(-1) dobutamine. Wall thickening (WT) was quantified using a method based on circumferential profile analysis. Left ventricular ejection fraction (LVEF) was obtained using the Cedars-Sinai algorithm. Blood pressure (BP) and heart rate (HR) were recorded at the end of each acquisition. At baseline LVEF, WT and systolic BP values under beta-blockade were not significantly different from those obtained in the non-beta-blocked state. The mean HR and diastolic BP at baseline were lower under beta-blockade. Dobutamine administration (at 5 and 10 microg kg(-1) min(-1)) induced a significant increase in WT, LVEF and systolic BP in all subjects both on and off beta-blockade. The increases in WT, LVEF and systolic BP in the beta-blocked state were less pronounced but not significantly different. HR increased significantly at 10 microg kg(-1) min(-1) dobutamine without beta-blocker administration, while no increase in HR was observed in the beta-blocked state. Beta-blocker therapy in healthy subjects attenuates the inotropic and chronotropic myocardial response to low-dose dobutamine. At doses of 5 and 10 microg kg(-1) min(-1) dobutamine, however, significant increases in global and regional left ventricular function can still be measured using consecutive gated SPET myocardial perfusion scintigraphy acquisitions even under beta-blocker therapy.     

Limited myocardial perfusion reserve in patients with left ventricular hypertrophy

Experimental studies in animals have suggested that coronary flow reserve may be limited in patients with left ventricular hypertrophy (LVH). Accordingly, to noninvasively determine the effect of LVH on myocardial perfusion reserve, 25 patients, 9 with LVH and 16 controls, underwent positron imaging with rubidium-82 (82Rb) (30-55 mCi) or nitrogen-13 (13N) ammonia (12-19 mCi) at rest and following intravenous dipyridamole and handgrip stress. LVH was documented by echocardiographic and/or electrocardiographic measurements. LVH patients had either no chest pain (n = 8) and/or a normal coronary angiogram (n = 6). Nine simultaneous transaxial images were acquired, and the mean ratio of stress to rest activity (S:R), based on all regions for each heart, was calculated as an estimate of myocardial perfusion reserve. There were no regional differences in activity (i.e., perfusion defects) in any of the studies. S:R averaged 1.41 +/- 0.10 (s.d.) for controls and 1.06 +/- 0.09 for patients with LVH (p less than 0.0001). These data provide support for an abnormality in perfusion reserve in patients with LVH.     

Repeatability of automatic left ventricular cavity volume measurements from myocardial perfusion SPECT

Background

This study sought to assess the repeatability of automatic quantitative measurements of left ventricular (LV) cavity volumes in a large patient population (N=926), to correlate those measurements to similarly obtained LV ejection fraction (LVEF) measurements, and to investigate the relationship between ungated and gated volumes.

Methods

All 926 patients underwent ungated single photon emission computed tomography (SPECT) immediately followed by 8-frame gated SPECT. LV cavity volumes were automatically measured from ungated (V), summed gated (SUMV), end-systolic (ESV) and end-diastolic (EDV) images, and LVEFs derived from the latter 2.

Results

Repeatability (SUMV vs V) was very good overall (6.4%±6.6%), further improving for volumes >25 mL (5.7%±5.5%) and >40 mL (5.2%±5.0%). Exponential regression between ESV and LVEF (r=0.925, SEE=15.0 mL) EDV and LVEF (r=0.802, SEE=24.2 mL), and SUMV and LVEF (r=0.867, SEE=19.7 mL) was also very good. Summed gated volumes were closer to ESV than to EDV (43.3%±8.8% of EDV-ESV range). SUMV <50 mL and SUMV >110 mL were good substitutes for LVEF >50% and LVEF <40% (93.4% and 97.1%, respectively).

Conclusion

Automatic quantitative measurements of gated and ungated volumes with our algorithm are repeatable, correlate well with other global myocardial parameters, and may contribute important additional information to that conventionally provided by myocardial perfusion SPECT studies.     

Comparison of methods for quantification of transient ischaemic dilation in myocardial perfusion SPET

The purpose of this study was to compare six methods of measuring the left ventricular (LV) transient ischaemic dilation (TID) ratio during stress-rest myocardial perfusion single-photon emission tomography (SPET). The TID ratio was defined as the mean LV short-axis area at stress divided by the mean LV area of similar slices at rest. The centre of the LV wall was defined as either the maximum, mean or median of the radial short-axis count profiles. The area within the endocardial wall was also calculated for each definition of the LV wall centre. We identified 50 consecutive patients undergoing dipyridamole technetium-99m-tetrofosmin SPET imaging and angiography. Continuous receiver operating characteristic (CROC) analysis showed no significant difference between the six methods in terms of identifying severe coronary artery disease (P >0.47). Algorithms using the mean or the median value in the profile were significantly more robust than those using the maximum (P <0.0005). TID measured by all the algorithms is an indicator of severe coronary disease (P < 0.05). The algorithms compared provide a repeatable, quantitative and specific measure of the TID ratio.     

Effect of the number of projections collected on quantitative perfusion and left ventricular ejection fraction measurements from gated myocardial perfusion single-photon emission computed tomographic images

Background

Gated myocardial perfusion single-photon emission computed tomographic (SPECT) imaging is currently performed by step-and-shoot detector rotation, resulting in acquisition dead time and lengthened study duration compared with nongated SPECT imaging with continuous or pseudocontinuous rotation. Dead time is particularly undesirable in new fast-gated SPECT imaging protocols with inotropic pharmacologic stress.

Methods and Results

This article evaluated the influence of projections’ angular spacing on quantitative measurements of left ventricular ejection fraction (LVEF) and perfusion from postexercise ^99mTc-labeled sestamibi images. Gated 60-projection data sets from 30 patients were compacted into 30- and 15-projection sets. The three sets (corresponding to 3-, 6-, and 12-degree spacing over 180 degrees) were reconstructed into gated and ungated short-axis image sets. LVEFs were measured from the gated images according to a previously described automatic algorithm, whereas perfusion was assessed from the ungated images by a 20-segment division of their maximal pixel polar maps. LVEF values were essentially unchanged between 60- and 30-projection images (y=0.37+0.996x; r=0.999; standard error of the estimate=0.56) and 60- and 15-projection images (y=1.35+0.987x; r=0.999; standard error of the estimate=0.77) in the 30 patients. Overall, 30- and 15-projection polar maps differed by 1.87%±1.24% and 4.38%±2.25% from the 60-projection polar maps, respectively. Segmental perfusion score agreement between 60- and 30-projection images and between 60- and 15-projection images was 93% (κ=0.92; p<0.001) and 83% (κ=0.81; p<0.001), respectively. Sixty- and 30-projection images were visually undistinguishable, whereas loss of image resolution was noticed in many 15-projection gated and ungated images.

Conclusions

Thirty-projection gated SPECT imaging is a practical, accurate, and time-saving approach in standard gated protocols and, potentially, fast-gated protocols. Fifteen-projection gated SPECT imaging is not generally recommended and should be considered only for LVEF assessment in conjunction with fast-gated protocols.     

The role of left ventricular hypertrophy and diabetes in the presence of transient ischemic dilation of the left ventricle on myocardial perfusion SPECT images.

Transient ischemic dilation of the left ventricle found on SPECT myocardial perfusion imaging (MPI) is an accepted marker of severe and extensive coronary artery disease (CAD) and poor prognosis. The influence of other clinical variables on the incidence of transient ischemic dilation is less certain. The aim of this study was to investigate clinical factors that may influence the incidence of transient ischemic dilation. In particular, we looked at factors that may independently affect subendocardial perfusion, such as left ventricular hypertrophy (LVH) and diabetes. METHODS: MPI studies of 103 consecutive patients who had undergone recent coronary angiography (< or =6 mo) and transthoracic echocardiography within a year of stress electrocardiography-gated MPI were retrospectively analyzed. Transient ischemic dilation was assessed quantitatively using a software program. A ratio cutoff of > or =1.22 was considered to represent transient ischemic dilation. Summed stress score and summed difference score (ischemia score) were determined using the standard 17-segment 5-point scoring system to quantify myocardial ischemia. LVH was defined as a left ventricular wall thickness of >11 mm on M-mode echocardiography. Severe CAD was defined as severe stenosis (> or =90%) of either the left anterior descending artery or both the right coronary and lateral circumflex arteries. RESULTS: Nineteen (18%) of the 103 patients had transient ischemic dilation, 19 (18%) had LVH, and 23 (22%) were diabetic. A high percentage had severe CAD (46/103 [45%]), whereas 57 of 103 (55%) had less severe CAD (30/103 [29%]) or nonsignificant CAD (26/103 [25%]). Severe CAD (P < 0.001), diabetes (P < 0.0001), LVH (P < 0.003), and the ischemia score (P < 0.023) were independent predictors of transient ischemic dilation by multivariate logistic regression. In patients with severe CAD, the effect of LVH on the incidence of transient ischemic dilation was additive, increasing the incidence from 21% (8/38) without LVH to 75% (6/8) with LVH (P < 0.006). Likewise, with severe CAD, the incidence of transient ischemic dilation rose from 21% (7/33) in patients without diabetes to 54% (7/13) in those with diabetes (P < 0.04). CONCLUSION: The presence of transient ischemic dilation on myocardial perfusion SPECT is associated with the presence of severe CAD, but this association is modified by the presence of LVH and diabetes.