|Year : 2010 | Volume
| Issue : 4 | Page : 156-159
Do reconstruction filters really effect the volume and ejection fraction calculation with 99m Tc-sestamibi-gated myocardial SPECT?
Manish Ora, Subhash Chand Kheruka, Sukanta Barai, Sanjay Gambhir
Department of Nuclear Medicine, SGPGIMS, Lucknow, India
|Date of Web Publication||23-Mar-2011|
Subhash Chand Kheruka
Department of Nuclear Medicine, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Rae Bareli Road, Lucknow-226 014
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background : ECG -gated myocardial perfusion imaging is a sensitive test for diagnosis of ischemia as well as scarred myocardium. It provides additional information on global and regional myocardial contractile function. A number of methods are available to calculate left ventricular volumes and ejection fractions, which depends on various technical and patients specific factor. Objective: This study was carried out to measure effect of reconstruction filter in calculations of left ventricularend diastolic volume (EDV) and end systolic volume (ESV) and left ventricular ejection fraction (LVEF) from 99mTc-sestamibi myocardial perfusion imaging. Materials and Methods: 99mTc-sestamibi-gated SPECT myocardial perfusion imaging was performed in 90 patients. Studies were reconstructed with Butterworth and Metz filters. Results: Mean ejection fraction with Butterworth and Metz filter are 64.3 and 64.2, respectively. Mean EDV is for Butterworth and Metz filters are 77.3 and 78.5 ml, respectively. While ESV was 36.49 and 36.63 ml, stroke volume calculated was 41.54 and 42 ml for Butterworth and Metz filters,respectively. Pearsons's correlation coefficients between results calculated with Metz and Butterworth filters were 0.994 for ESV, 0.996 for EDV, 0.966 for LVEF and 0.925 for SV. Student 't' test was applied on the data and no significant difference was noted between parameter estimated by Butterworth or Metz filter. Conclusion: This study shows that difference of filter application has no significant effect in computing left ventricular function parameters.
Keywords: Butterworth, ejection fraction, Metz, Myocardial perfusion imaging, reconstruction filter
|How to cite this article:|
Ora M, Kheruka SC, Barai S, Gambhir S. Do reconstruction filters really effect the volume and ejection fraction calculation with 99m Tc-sestamibi-gated myocardial SPECT?. Indian J Nucl Med 2010;25:156-9
|How to cite this URL:|
Ora M, Kheruka SC, Barai S, Gambhir S. Do reconstruction filters really effect the volume and ejection fraction calculation with 99m Tc-sestamibi-gated myocardial SPECT?. Indian J Nucl Med [serial online] 2010 [cited 2020 Mar 31];25:156-9. Available from: http://www.ijnm.in/text.asp?2010/25/4/156/78251
| Introduction|| |
Myocardial perfusion imaging is a sensitive test for diagnosis of ischemia as well as scarred myocardium. Electrocardiography (ECG)-gated imaging provides additional information on global and regional myocardial contractile function,  and allows the calculation of left ventricular end diastolic volume (EDV), end systolic volume (ESV), stroke volume (SV) and ejection fraction (LVEF).  This functional information gives additional prognostic information
A number of methods are available to calculate left-ventricular volumes and ejection fractions. , Various volumes and ejection fraction calculated depended on software used,  calculation method used, acquisition parameter such as number of frames,  zoom factor,  filter used for image reconstruction. , The accuracy of results may also be affected by patient-specific factors such as cardiac volume, patient size and perfusion defect size. 
It has been emphasized that the effect of changing filter may invalidate the clinical parameter. This study was carried out to measure effect of reconstruction filter in calculations of left-ventricular EDV and ESV and LVEF from 99m Tc-sestamibi myocardial perfusion imaging.
| Materials and Methods|| |
Patients 99m Tc-sestamibi-gated SPECT myocardial perfusion imaging was performed in 90 patients.
Gated SPECT acquisition
Myocardial gated SPECT was carried out 1 hour after intravenous injection of 400 MBq 99m Tc-sestamibi. SPECT acquisition was carried out on a dual-head large field of view γ-camera (DXTXL SMV). Sixty-four projections (32 per head) were obtained in 64×64 matrices using a step and shoot acquisition over a 180º arc from right anterior oblique to left posterior oblique position. Acquisition zoom was 1.33, giving a pixel size of 6.7 mm. All studies were acquired with 16 frames per cardiac cycle using an R-wave trigger and a 40% acceptance window.
Gated SPECT data processing
Studies were processed on a Xeleris version 1.330. Images were pre-filtered, and then reconstructed by filtered back-projection with a ramp filter. Two filters recommended by the manufacturer for reconstruction of gated SPECT studies, Butterworth order 10, cut-off frequency 0.394 cycles/pixel and Metz order 3.25, full-width half-maximum 2.35 mm, were compared. The former is a low pass filter, while the latter is an edge-enhancement filter. Both these types of filter have been shown to be effective in reconstructing SPECT studies. Myocardial EDV (ml) and ESV (ml), SV (ml) and LVEF (%) were determined using a commercial semi-automatic gated SPECT processing software, Emory toolbox. Processing was performed by a single operator for each study using the two filters concurrently
Statistical analysis was performed with the SPSS program version 13 for Windows. The Spearman rank correlation coefficient was used to test for correlations. The individual differences for each patient between filtering with Metz and Butterworth filters were calculated, and statistical differences were tested for using a paired t-test.
| Result|| |
The ESV and EDV, SV and LVEF are shown in [Table 1]. Mean ejection fraction with Butterworth and Metz filter are 64.3 and 64.2. Mean EDV is for Butterworth and Metz filters are 77.3 and 78.5 ml. While ESV was 36.49 and 36.63 ml, SV calculated was 41.54 and 42 ml for Butterworth and Metz filters, respectively. Pearsons's correlation coefficients between results calculated with Metz and Butterworth filters were 0.994 for ESV, 0.996 for EDV, 0.966 for LVEF and 0.925 for SV [Figure 1],[Figure 2],[Figure 3].
|Table 1: Different cardiac volume measured by Butterworth and Metz filter|
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|Figure 1: Bar diagram representing different parameter measured from Butterworth and Metz filter|
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|Figure 2: Linear bar diagram to show correlation of EF, EDV, ESV and SV measured by Butterworth and Metz filter|
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|Figure 3: Scatter diagram showing correlation between ejection fraction measured from both filters|
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Student 't' test was applied on the data and no significant difference was noted between parameter estimated by Butterworth or Metz filter [Table 2].
| Discussion|| |
During processing of ECG gated Myocardiac perfusion imaging quantification starts with the detection of the LV endocardial and epicardial boundaries. Most algorithms first estimate the location of the midmyocardium, which corresponds to the maximal myocardial count. From the midmyocardial points, endocardial and epicardial boundaries can be extracted either by using a fixed number of SDs of gaussian fitting to the myocardial count profile , or using a predefined count threshold based on the phantom data.  Once the definitions of the endocardial and epicardial edges are achieved, LV volume is calculated by multiplying the number of pixels within the LV cavity with the size of a pixel. LV volume can be generated for each of the frames in the cardiac cycle. The largest volume and the smallest volume represent the EDV and the ESV, respectively. LVEF is derived from the volumes using the formula (EDV - ESV)/EDV ×100.
As endocardial edge is found from the maximum slope of the profile between the cardiac center and the wall center,  which would be expected to vary with filter, and to give a thicker wall measurement with a smoother filter.  A thicker wall will lead to a smaller cardiac volume, and so volumes were expected to be smaller with the smoother Butterworth filter is comparison to sharper Metz filter. But we were not able to demonstrate this difference is our study. We expected that the difference in wall thickness would be comparable in both end-diastole and end-systole, so the SV would not be affected by the filter that was found true later in study. As both EDV and ESV are not affected by application of different filter so EF is also same.
The result of this study is in contrast with that of observed by Vakhtangandze et al,  and Wright A  et al, which have shown that smoother reconstruction filters lead to lower volumes and higher ejection fractions. Although excellent correlation was noted between the filters but the difference was significant statistically. Number of patients was 30 and 40 in these studies. Mean difference of ejection fraction was -3.5 ± 0.9 (Metz and Butterworth) and 2.55 ± 3.10% (Butterworth and Hann filter). This difference may be statistically significant but unlikely to be clinically significant.
LVEF is a has been established as an indicator of prognosis after myocardial infarction  and heart failure.  ESV is the most sensitive parameter in determining improvement in left ventricular function after revascularization.  Left ventricular volumes can be measured by radionuclide ventriculography. White et al, also focusing on patients with recent myocardial infarction demonstrated that besides LVEF, left ventricular volumes are important in the prediction of survival. Progressive increments of 25 ml in ESV augmented the relative risk of cardiac death in an exponential fashion: as compared to patients with a normal ESV (30-55 ml), patients with an ESV of 75 ml and 125 ml had a 2.5-fold and a 5-fold higher relative risk of cardiac death, respectively. 
Gated cardiac scan has one additional advantage of increasing specificity of myocardiac perfusion imaging. As perfusion-scan fixed defects may result from soft tissue attenuation, decreasing test specificity for coronary disease and myocardial infarction (MI). Gated 99m Tc-sestamibi SPECT may help differentiate MI from artifact since fixed defects with decreased function (wall motion and thickening) probably represent MI, whereas attenuation artifacts either have normal function or at least do not demonstrate markedly reduced function. 
| Conclusion|| |
There were no statistically significant mean differences in EDV, ESV, LVEF and SV measured using Butterworth and Metz filters. The differences found in our study are dissimilar to those from previous studies comparing reconstruction with different filters. , The correlations between two filters were good for all functional parameter.
These results show that difference of filter application has no major effect on left ventricular function parameter.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]