TECHNOLOGIST CORNER Technical aspects of resolution recovery reconstruction Robert Pagnanelli, BSRT(R)(N), CNMT, NCT, FASNC,a and Salvador Borges-Neto, MD, FASNCa a
Division of Nuclear Medicine, Department of Radiology, Duke University Medical Center, Durham, NC Received Nov 9, 2015; accepted Nov 16, 2015 doi:10.1007/s12350-015-0345-7
Technological advances in processing have allowed nuclear cardiology labs to increase efficiency as well as reduce radiation exposure to both patients and staff. With increased awareness on reduced radiation exposure, efficiency and quality resolution recovery reconstruction is a perfect fit for nuclear cardiology. Having a basic understanding of what is required as well as being aware of the potential pitfalls can provide some clarity on how to incorporate resolution recovery reconstruction into the existing workflow of a nuclear cardiology lab. Key Words: Image reconstruction Æ image processing Æ myocardial perfusion imaging Æ SPECT Æ radiation reduction
Over the last few years, nuclear cardiology has seen significant hardware and software advancement for acquisition and processing. These technological advances have allowed nuclear cardiology labs to increase efficiency as well as reduce radiation exposure to both patients and staff. However, the incorporation of new tools into clinical practice raises questions. These advancements have shown to go somewhat against the most fundamental acquisition principle the technologists learn in training, more counts are better. As with any new hardware or software used in nuclear cardiology, training is recommended. It typically provides basic instruction, however, stops short of suggesting dosing and scan times. Over the past several years, there has been increased pressure to reduce radiation exposure associated with diagnostic testing. In 2010, the American Society of
Reprint requests: Robert Pagnanelli, BSRT(R)(N), CNMT, NCT, FASNC, Division of Nuclear Medicine, Department of Radiology, Duke University Medical Center, 2301 Erwin Rd, Durham, NC 27710; [email protected] J Nucl Cardiol 2016;23:149–52. 1071-3581/$34.00 Copyright Ó 2015 American Society of Nuclear Cardiology.
Nuclear Cardiology published an information statement on recommendations for reducing radiation exposure in myocardial perfusion imaging concluding that for the population of patients referred for SPECT or PET myocardial perfusion imaging, on average a total radiation exposure of B9 mSv is achieved in 50% of studies by 2014.1 Resolution recovery reconstruction algorithms are a critical component toward reaching this goal. Resolution recovery reconstructions for nuclear cardiology studies incorporate specifics from the imaging device into the reconstruction. These include but are not limited to the intrinsic resolution of the camera and the specifications of the collimator such as the width and length of the bores. The distance of the detectors from the center of rotation during an acquisition is considered. UltraSPECTTM (Auburndale, MA) is a unique resolution recovery reconstruction algorithm in that it is compatible with almost all recently manufactured conventional gamma cameras for myocardial perfusion imaging. It only requires the addition of a computer to the imaging network. The software contains the detail of most gamma camera models and their collimators. The software configuration uses drop-down menus to select the camera vendor, vendor model name, and collimators being used for acquisitions. Dataset names are associated with each. Information for several imaging devices can be configured into the software. Once complete, the 149
150
Pagnanelli and Borges-Neto Technical aspects of resolution recovery reconstruction
software then will customize the resolution recovery for each SPECT acquisition. Acquired data from the gamma camera are transferred to the UltraSPECTTM computer where it is reconstructed. Transaxial images are sent from that device to the processing station for realignment and interpretation. The major hardware vendors for nuclear medicine have similar products proprietary to their systems. These resolution recovery algorithms do not require configuration as the information is embedded for that specific vendor. General Electric offers their EvolutionTM (Waukesha, WI) software, while Philips offers AstonishTM (Eindhoven, Netherlands). Both EvolutionTM and AstonishTM allow incorporation of attenuation correction maps to the reconstruction. Whether for a nonvendor-specific software such as UltraSPECTTM or for the software proprietary of a camera vendor, it is not recommended to change the default settings for the reconstruction as the software was validated on these preset settings. Most new resolution recovery reconstruction algorithms have been well validated,2-4 although the literature varies slightly on each algorithm. The consensus is that SPECT myocardial perfusion imaging is completed with these resolution recovery reconstruction algorithms using one-half of the standard counts which can be the result of reduced administered dose or acquisition time. Some may allow one quarter count studies. For a patient with an average BMI (body mass index), conventional protocols for Tc-99m one-day rest/ stress or stress/rest studies performed on dual-headed SPECT systems with detectors in a 90-degree orientation suggest doses of 10 and 30 millicuries, respectively.5 Low-dose studies are scanned for 30 s/ step that total approximately 16 minutes. High-dose studies are scanned for 20 s/step that total approximately 12 minutes. Conventional (nonresolution recovery) reconstruction is performed with filtered back projection or iterative reconstruction (Figure 1). When utilizing a recovery reconstruction algorithm in our lab, counts are reduced by half resulting in at least comparable if not an improvement in technical quality. Thus, at Duke, we either keep all acquisition parameters the same reducing the doses by half, to 5 and 15 millicuries (Figure 2), or we keep the doses the same, 10 and 30 millicuries, and the acquisition time reduces to 15 s/step for the low dose, which reduces the total acquisition time to approximately 8 minutes. The high-dose study would be reduced to 10 s/step for acquisition time totaling approximately 6 minutes (Figure 3). All other acquisition parameters used are consistent with the American Society of Nuclear Cardiology guidelines including
Journal of Nuclear CardiologyÒ January/February 2016
three-degree steps, a 180-degree orbit, a 64 9 64 matrix, high-resolution collimators, and eight frame/cycle for gated SPECT. Most often, labs are taking advantage of the lower administered doses; however, the benefit of shorter scan times is useful for claustrophobic and less compliant patients. These protocols are listed in Table 1. Resolution recovery software is embedded in the iterative reconstruction algorithm. Resolution recovery reconstruction is not compatible with filtered back projection. Images reconstructed with resolution recovery algorithms are different from images reconstructed with iterative reconstruction alone or filtered back projection. There will be a learning curve for interpreting physicians. Thresholds will likely change for calling perfusion abnormalities. For training purposes, labs should strongly consider acquiring and processing several studies both with a conventional protocol as well as with a shortened acquisition and processing with resolution recovery software. This will allow both the technologist and physician to assure that study quality at least is maintained with the lower count studies. In addition, it will allow interpreting physicians to see differences in the images as a result of the varying protocols. In general, compared to standard acquisition and processing, images processed with the resolution recovery software will likely have better contrast and resolution. Most likely, fewer counts will be seen in the left ventricular cavity. Interpreting physicians at our facility agree that true perfusion abnormalities are more pronounced with the resolution recovery reconstruction than with filtered back projection. Likewise, motion artifacts tend to be more conspicuous. The left ventricular walls will likely appear thinner and, therefore, the left ventricular cavity will appear larger. Quantitative data are somewhat contradictory and have shown left ventricular volumes to be significantly larger with filtered backprojection than with resolution recovery software although the volumes had a high correlation.2 The default manufacturer study databases loaded in older versions of quantitative analysis software are from studies performed using conventional protocols and standard administered radiopharmaceutical doses. Also, they are built from studies that are reconstructed with filtered backprojection. That database is therefore no longer appropriate for accurate quantitative analysis of resolution recovery reconstructed studies. A new normal database created from patients acquired with reduced counts and processed with resolution recovery has not yet been built in our lab. With experienced readers, it is not a regularly utilized tool. However, in labs where there is significant guidance in the interpretation from the quantitative data results, a normal database reflective
Journal of Nuclear CardiologyÒ Volume 23, Number 1;149–52
Pagnanelli and Borges-Neto Technical aspects of resolution recovery reconstruction
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Figure 1. Conventional. Rest and stress short axis images were acquired using both standard scan times and radiopharmaceutical doses. They are reconstructed using filtered back projection. Images demonstrate ischemia in the mid-anterior wall related to a diagonal lesion.
Figure 2. Full scan/half dose. Rest and stress short axis images were acquired using standard scan times and with one half of the standard administered radiopharmaceutical doses. Processing is with resolution recovery. Images demonstrate normal perfusion.
of the specific acquisition and processing techniques should be created when not provided by newer software versions. Most technologists and physicians have less experience with resolution recovery reconstruction algorithms than with conventional processing such as filtered back projection or iterative reconstruction. Understanding what the software is designed to
accomplish as well as its capabilities are important. With increased awareness of reduced radiation exposure, efficiency, and quality, resolution recovery reconstruction is a perfect fit for the nuclear cardiology field. Increased use and experience with this resolution recovery algorithm will continue to promote this technology as the new standard in nuclear cardiology imaging.
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Pagnanelli and Borges-Neto Technical aspects of resolution recovery reconstruction
Journal of Nuclear CardiologyÒ January/February 2016
Figure 3. Half scan/full dose. Rest and stress short axis images were acquired using one half of the standard scan times and standard radiopharmaceutical doses. Processing is with resolution recovery. It is the same patient as in Figure 1.
Table 1. Comparison of acquisition protocols
Conventional Full scan/half dose RR Half scan/full dose RR
Rest dose, mCi
Rest time/ step, s
Rest scan total, min
Stress dose, mCi
Stress time/ step, s
10 5
30 30
16 16
30 15
20 20
12 12
12 6
10
15
8
30
10
6
12
References 1. Cerqueira MD, Allman KC, Ficaro EP, Hansen CL, Nichols KJ, Thompson RC, et al. Recommendations for reducing radiation exposure in myocardial perfusion imaging. J Nucl Cardiol 2010;17:709-18. 2. Borges-Neto S, Pagnanelli R, Shaw LK, Honeycutt E, Shwartz SC, Adams G, et al. Clinical results of a novel wide beam reconstruction method for shortening scan time of cardiac SPECT perfusion studies. J Nucl Cardiol 2007;14:555-65. 3. Venero CV, Heller GV, Bateman TM, McGhie AL, Ahlberg AW, Katten D, et al. A multicenter evaluation of a new post-processing
Stress scan Effective dose total, min RST/STR, mSv
method with depth-dependent collimator resolution applied to fulltime and half-time acquisitions without and with simultaneously acquired attenuation correction. J Nucl Cardiol 2009;16:714-25 Erratum in J Nucl Cardiol 2010;17:706. 4. Belhocine T, Gambhir S, Brenner R, Peretz A, Driedger A, Urbain JL. Half-time resolution recovery package for SPECT-CT MPI: A pilot study. J Nucl Med 2007;48:234. 5. Henzolva MJ, Cerqueira MD, Hansen CL, Taillefer R, Yao SS, et al. ASNC imaging guidelines: Stress protocols and tracers. J Nucl Cardiol 2009;10:25-37.
Division of Nuclear Medicine, Department of Radiology, Duke University Medical Center, Durham, NC Received Nov 9, 2015; accepted Nov 16, 2015 doi:10.1007/s12350-015-0345-7
Technological advances in processing have allowed nuclear cardiology labs to increase efficiency as well as reduce radiation exposure to both patients and staff. With increased awareness on reduced radiation exposure, efficiency and quality resolution recovery reconstruction is a perfect fit for nuclear cardiology. Having a basic understanding of what is required as well as being aware of the potential pitfalls can provide some clarity on how to incorporate resolution recovery reconstruction into the existing workflow of a nuclear cardiology lab. Key Words: Image reconstruction Æ image processing Æ myocardial perfusion imaging Æ SPECT Æ radiation reduction
Over the last few years, nuclear cardiology has seen significant hardware and software advancement for acquisition and processing. These technological advances have allowed nuclear cardiology labs to increase efficiency as well as reduce radiation exposure to both patients and staff. However, the incorporation of new tools into clinical practice raises questions. These advancements have shown to go somewhat against the most fundamental acquisition principle the technologists learn in training, more counts are better. As with any new hardware or software used in nuclear cardiology, training is recommended. It typically provides basic instruction, however, stops short of suggesting dosing and scan times. Over the past several years, there has been increased pressure to reduce radiation exposure associated with diagnostic testing. In 2010, the American Society of
Reprint requests: Robert Pagnanelli, BSRT(R)(N), CNMT, NCT, FASNC, Division of Nuclear Medicine, Department of Radiology, Duke University Medical Center, 2301 Erwin Rd, Durham, NC 27710; [email protected] J Nucl Cardiol 2016;23:149–52. 1071-3581/$34.00 Copyright Ó 2015 American Society of Nuclear Cardiology.
Nuclear Cardiology published an information statement on recommendations for reducing radiation exposure in myocardial perfusion imaging concluding that for the population of patients referred for SPECT or PET myocardial perfusion imaging, on average a total radiation exposure of B9 mSv is achieved in 50% of studies by 2014.1 Resolution recovery reconstruction algorithms are a critical component toward reaching this goal. Resolution recovery reconstructions for nuclear cardiology studies incorporate specifics from the imaging device into the reconstruction. These include but are not limited to the intrinsic resolution of the camera and the specifications of the collimator such as the width and length of the bores. The distance of the detectors from the center of rotation during an acquisition is considered. UltraSPECTTM (Auburndale, MA) is a unique resolution recovery reconstruction algorithm in that it is compatible with almost all recently manufactured conventional gamma cameras for myocardial perfusion imaging. It only requires the addition of a computer to the imaging network. The software contains the detail of most gamma camera models and their collimators. The software configuration uses drop-down menus to select the camera vendor, vendor model name, and collimators being used for acquisitions. Dataset names are associated with each. Information for several imaging devices can be configured into the software. Once complete, the 149
150
Pagnanelli and Borges-Neto Technical aspects of resolution recovery reconstruction
software then will customize the resolution recovery for each SPECT acquisition. Acquired data from the gamma camera are transferred to the UltraSPECTTM computer where it is reconstructed. Transaxial images are sent from that device to the processing station for realignment and interpretation. The major hardware vendors for nuclear medicine have similar products proprietary to their systems. These resolution recovery algorithms do not require configuration as the information is embedded for that specific vendor. General Electric offers their EvolutionTM (Waukesha, WI) software, while Philips offers AstonishTM (Eindhoven, Netherlands). Both EvolutionTM and AstonishTM allow incorporation of attenuation correction maps to the reconstruction. Whether for a nonvendor-specific software such as UltraSPECTTM or for the software proprietary of a camera vendor, it is not recommended to change the default settings for the reconstruction as the software was validated on these preset settings. Most new resolution recovery reconstruction algorithms have been well validated,2-4 although the literature varies slightly on each algorithm. The consensus is that SPECT myocardial perfusion imaging is completed with these resolution recovery reconstruction algorithms using one-half of the standard counts which can be the result of reduced administered dose or acquisition time. Some may allow one quarter count studies. For a patient with an average BMI (body mass index), conventional protocols for Tc-99m one-day rest/ stress or stress/rest studies performed on dual-headed SPECT systems with detectors in a 90-degree orientation suggest doses of 10 and 30 millicuries, respectively.5 Low-dose studies are scanned for 30 s/ step that total approximately 16 minutes. High-dose studies are scanned for 20 s/step that total approximately 12 minutes. Conventional (nonresolution recovery) reconstruction is performed with filtered back projection or iterative reconstruction (Figure 1). When utilizing a recovery reconstruction algorithm in our lab, counts are reduced by half resulting in at least comparable if not an improvement in technical quality. Thus, at Duke, we either keep all acquisition parameters the same reducing the doses by half, to 5 and 15 millicuries (Figure 2), or we keep the doses the same, 10 and 30 millicuries, and the acquisition time reduces to 15 s/step for the low dose, which reduces the total acquisition time to approximately 8 minutes. The high-dose study would be reduced to 10 s/step for acquisition time totaling approximately 6 minutes (Figure 3). All other acquisition parameters used are consistent with the American Society of Nuclear Cardiology guidelines including
Journal of Nuclear CardiologyÒ January/February 2016
three-degree steps, a 180-degree orbit, a 64 9 64 matrix, high-resolution collimators, and eight frame/cycle for gated SPECT. Most often, labs are taking advantage of the lower administered doses; however, the benefit of shorter scan times is useful for claustrophobic and less compliant patients. These protocols are listed in Table 1. Resolution recovery software is embedded in the iterative reconstruction algorithm. Resolution recovery reconstruction is not compatible with filtered back projection. Images reconstructed with resolution recovery algorithms are different from images reconstructed with iterative reconstruction alone or filtered back projection. There will be a learning curve for interpreting physicians. Thresholds will likely change for calling perfusion abnormalities. For training purposes, labs should strongly consider acquiring and processing several studies both with a conventional protocol as well as with a shortened acquisition and processing with resolution recovery software. This will allow both the technologist and physician to assure that study quality at least is maintained with the lower count studies. In addition, it will allow interpreting physicians to see differences in the images as a result of the varying protocols. In general, compared to standard acquisition and processing, images processed with the resolution recovery software will likely have better contrast and resolution. Most likely, fewer counts will be seen in the left ventricular cavity. Interpreting physicians at our facility agree that true perfusion abnormalities are more pronounced with the resolution recovery reconstruction than with filtered back projection. Likewise, motion artifacts tend to be more conspicuous. The left ventricular walls will likely appear thinner and, therefore, the left ventricular cavity will appear larger. Quantitative data are somewhat contradictory and have shown left ventricular volumes to be significantly larger with filtered backprojection than with resolution recovery software although the volumes had a high correlation.2 The default manufacturer study databases loaded in older versions of quantitative analysis software are from studies performed using conventional protocols and standard administered radiopharmaceutical doses. Also, they are built from studies that are reconstructed with filtered backprojection. That database is therefore no longer appropriate for accurate quantitative analysis of resolution recovery reconstructed studies. A new normal database created from patients acquired with reduced counts and processed with resolution recovery has not yet been built in our lab. With experienced readers, it is not a regularly utilized tool. However, in labs where there is significant guidance in the interpretation from the quantitative data results, a normal database reflective
Journal of Nuclear CardiologyÒ Volume 23, Number 1;149–52
Pagnanelli and Borges-Neto Technical aspects of resolution recovery reconstruction
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Figure 1. Conventional. Rest and stress short axis images were acquired using both standard scan times and radiopharmaceutical doses. They are reconstructed using filtered back projection. Images demonstrate ischemia in the mid-anterior wall related to a diagonal lesion.
Figure 2. Full scan/half dose. Rest and stress short axis images were acquired using standard scan times and with one half of the standard administered radiopharmaceutical doses. Processing is with resolution recovery. Images demonstrate normal perfusion.
of the specific acquisition and processing techniques should be created when not provided by newer software versions. Most technologists and physicians have less experience with resolution recovery reconstruction algorithms than with conventional processing such as filtered back projection or iterative reconstruction. Understanding what the software is designed to
accomplish as well as its capabilities are important. With increased awareness of reduced radiation exposure, efficiency, and quality, resolution recovery reconstruction is a perfect fit for the nuclear cardiology field. Increased use and experience with this resolution recovery algorithm will continue to promote this technology as the new standard in nuclear cardiology imaging.
152
Pagnanelli and Borges-Neto Technical aspects of resolution recovery reconstruction
Journal of Nuclear CardiologyÒ January/February 2016
Figure 3. Half scan/full dose. Rest and stress short axis images were acquired using one half of the standard scan times and standard radiopharmaceutical doses. Processing is with resolution recovery. It is the same patient as in Figure 1.
Table 1. Comparison of acquisition protocols
Conventional Full scan/half dose RR Half scan/full dose RR
Rest dose, mCi
Rest time/ step, s
Rest scan total, min
Stress dose, mCi
Stress time/ step, s
10 5
30 30
16 16
30 15
20 20
12 12
12 6
10
15
8
30
10
6
12
References 1. Cerqueira MD, Allman KC, Ficaro EP, Hansen CL, Nichols KJ, Thompson RC, et al. Recommendations for reducing radiation exposure in myocardial perfusion imaging. J Nucl Cardiol 2010;17:709-18. 2. Borges-Neto S, Pagnanelli R, Shaw LK, Honeycutt E, Shwartz SC, Adams G, et al. Clinical results of a novel wide beam reconstruction method for shortening scan time of cardiac SPECT perfusion studies. J Nucl Cardiol 2007;14:555-65. 3. Venero CV, Heller GV, Bateman TM, McGhie AL, Ahlberg AW, Katten D, et al. A multicenter evaluation of a new post-processing
Stress scan Effective dose total, min RST/STR, mSv
method with depth-dependent collimator resolution applied to fulltime and half-time acquisitions without and with simultaneously acquired attenuation correction. J Nucl Cardiol 2009;16:714-25 Erratum in J Nucl Cardiol 2010;17:706. 4. Belhocine T, Gambhir S, Brenner R, Peretz A, Driedger A, Urbain JL. Half-time resolution recovery package for SPECT-CT MPI: A pilot study. J Nucl Med 2007;48:234. 5. Henzolva MJ, Cerqueira MD, Hansen CL, Taillefer R, Yao SS, et al. ASNC imaging guidelines: Stress protocols and tracers. J Nucl Cardiol 2009;10:25-37.
