Archived Comments for:
Superior diagnostic performance of perfusion-cardiovascular magnetic resonance versus SPECT to detect coronary artery disease: The secondary endpoints of the multicenter multivendor MR-IMPACT II (Magnetic Resonance Imaging for Myocardial Perfusion Assessment in Coronary Artery Disease Trial)
Wolfgang Schaefer, Kliniken Maria Hilf Mönchengladbach
21 April 2015
Schwitter et al report in their recently published paper a superiority of CMR over SPECT based on ROC analyses (1). For accurate interpretation of those results some comments on the used techniques are indispensable:
1. There were clear-cut restrictions concerning the CMR technique: even if different MR-scanners were used, only 1.5 Tesla machines were allowed. The CMR contrast agent itseld and its concentration were precisely defined. Furthermore, the study protocol was very strict regarding acquisition sequences. The application of state-of-the-art techniques "fast gradient-echo acquisition with an echo-planer component" was allowed "where available". In contrast to this, SPECT imaging was subject to restrictions concerning state-of-the-art techniques (2) e.g "Algorithms for attenuation correction or resolution recovery were not applied as these were not available or not identical over all sites". Apparently, SPECT could be done free-style based on the investigator's choice. There were no restrictions or specifications concerning the camera systems, radiotracer or the protocol. Therefore, we are concerned that this work reflects a head-to-head comparison of well selected, modern MR-sites to rather ordinary SPECT labs. This is underscored by the fact that only 253 of 465 SPECT investigations were gated, which, from our point of view, is an uncceptable low rate.
2. The grading of the perfusion abnormalities is straightforward for the MRI using a quasi-linear scale: severely abnormal (=3); moderately abnormal (=2); borderline abnormal defect (=1); or normal perfusion (=0). In contrast, grading of SPECT studies is somewhat arbitrary: reversible (=3), partially reversible (=2), fixed defect (=1), or normal (=0). For example, 5 segments with fixed defects result in a summed grading of 5, whereas 5 segments with reversible defects result in a summed grading of 15. This implies that 5 segments with reversible defects are rated 3 times more severe than 5 segments with fixed defects, which is hardly comprehensible. A positive TID is graded 3, but keeping in mind that a positive TID is a clear index for a severe multi-vessel-disease, the arbitrary value of 3 is absolutely underscored. This underlines the inadequacy of the SPECT grading used in this study. Consequently, the results of the ROC analyses have to be considered doubtful. From our point of view a simple linear grading e.g. SSS (3) - like published hundred times before - would have been much more accurate and adequate.
3. The statistics suffer from the fact, that multiple testings were done, but the necessary correction for multiple comparisons (e.g. Bonferroni correction) was ignored.
References, 1.Schwitter J, Wacker CM, Wilke N, et al. Superior diagnostic performance of perfusion-cardiovascular magnetic resonance versus SPECT to detect coronary artery disease: The secondary endpoints of the multicenter multivendor MR-IMPACT II (Magnetic Resonance Imaging for Myocardial Perfusion Assessment in Coronary Artery Disease Trial). J Cardiovasc Magn Reson. 2012;14:61.
2. Bateman TM, Heller GV, McGhie AI, et al. Multicenter investigation comparing a highly efficient half-time stress-only attenuation correction approach against standard rest-stress Tc-99m SPECT imaging. J Nucl Cardiol 2009;16:726-35
3. Knollmann D, Knebel I, Koch KC, et al. Comparison of SSS and SRS calculated from normal databases provided by QPS and 4D_MSPECT manufacturers and from identical institutional normals. Eur J Nucl Med Mol Imaging 2008;35:311-8
Wolfgang M. Schaefer 1 MD PhD
Daniela Knollmann 1 MD PhD
Philipp Meyer 2 Md PhD
1, Department of Nuclear Medicine, Maria Hilf Hospital, Monchengladbach, Germany 2. Department of Nuclear Medicine, University Hospital Freiburg, Germany
Corresponding address Prof. Dr. Dr. Wolfgang M Schaefer, MD PhD Department of Nuclear Medicine Maria Hilf Hospital Viersener Str. 450 41061 Mönchengladbach Germany email: wolfgang.schaefer@nuklearmedizin-mg.de Tel. +49-2161-8922430 Fax. +49-2161-8922417
Competing interests
Wolfgang M. Schaefer received honoraria as speaker and consultant from Covidien, Siemens, GE Healthcare and Philips Healthcare.
Daniele Knollmann received honoraria as a speaker from Siemens.
Philipp T. Meyer received research grants from GE Healthcare and honoraria for lectures by Siemens AG and consultancy by Bayer-Schering AG.
Letter to the Editor
21 April 2015
Schwitter et al report in their recently published paper a superiority of CMR over SPECT based on ROC analyses (1). For accurate interpretation of those results some comments on the used techniques are indispensable:
1. There were clear-cut restrictions concerning the CMR technique: even if different MR-scanners were used, only 1.5 Tesla machines were allowed. The CMR contrast agent itseld and its concentration were precisely defined. Furthermore, the study protocol was very strict regarding acquisition sequences. The application of state-of-the-art techniques "fast gradient-echo acquisition with an echo-planer component" was allowed "where available". In contrast to this, SPECT imaging was subject to restrictions concerning state-of-the-art techniques (2) e.g "Algorithms for attenuation correction or resolution recovery were not applied as these were not available or not identical over all sites". Apparently, SPECT could be done free-style based on the investigator's choice. There were no restrictions or specifications concerning the camera systems, radiotracer or the protocol. Therefore, we are concerned that this work reflects a head-to-head comparison of well selected, modern MR-sites to rather ordinary SPECT labs. This is underscored by the fact that only 253 of 465 SPECT investigations were gated, which, from our point of view, is an uncceptable low rate.
2. The grading of the perfusion abnormalities is straightforward for the MRI using a quasi-linear scale: severely abnormal (=3); moderately abnormal (=2); borderline abnormal defect (=1); or normal perfusion (=0). In contrast, grading of SPECT studies is somewhat arbitrary: reversible (=3), partially reversible (=2), fixed defect (=1), or normal (=0). For example, 5 segments with fixed defects result in a summed grading of 5, whereas 5 segments with reversible defects result in a summed grading of 15. This implies that 5 segments with reversible defects are rated 3 times more severe than 5 segments with fixed defects, which is hardly comprehensible. A positive TID is graded 3, but keeping in mind that a positive TID is a clear index for a severe multi-vessel-disease, the arbitrary value of 3 is absolutely underscored. This underlines the inadequacy of the SPECT grading used in this study. Consequently, the results of the ROC analyses have to be considered doubtful. From our point of view a simple linear grading e.g. SSS (3) - like published hundred times before - would have been much more accurate and adequate.
3. The statistics suffer from the fact, that multiple testings were done, but the necessary correction for multiple comparisons (e.g. Bonferroni correction) was ignored.
References,
1.Schwitter J, Wacker CM, Wilke N, et al. Superior diagnostic performance of perfusion-cardiovascular magnetic resonance versus SPECT to detect coronary artery disease: The secondary endpoints of the multicenter multivendor MR-IMPACT II (Magnetic Resonance Imaging for Myocardial Perfusion Assessment in Coronary Artery Disease Trial). J Cardiovasc Magn Reson. 2012;14:61.
2. Bateman TM, Heller GV, McGhie AI, et al. Multicenter investigation comparing a highly efficient half-time stress-only attenuation correction approach against standard rest-stress Tc-99m SPECT imaging. J Nucl Cardiol 2009;16:726-35
3. Knollmann D, Knebel I, Koch KC, et al. Comparison of SSS and SRS calculated from normal databases provided by QPS and 4D_MSPECT manufacturers and from identical institutional normals. Eur J Nucl Med Mol Imaging 2008;35:311-8
Wolfgang M. Schaefer 1 MD PhD
Daniela Knollmann 1 MD PhD
Philipp Meyer 2 Md PhD
1, Department of Nuclear Medicine, Maria Hilf Hospital, Monchengladbach, Germany
2. Department of Nuclear Medicine, University Hospital Freiburg, Germany
Corresponding address
Prof. Dr. Dr. Wolfgang M Schaefer, MD PhD
Department of Nuclear Medicine
Maria Hilf Hospital
Viersener Str. 450
41061 Mönchengladbach
Germany
email: wolfgang.schaefer@nuklearmedizin-mg.de
Tel. +49-2161-8922430
Fax. +49-2161-8922417
Competing interests