New techniques, distinctive population, unique normal databases

Journal of Nuclear Cardiology, May 2017

James R. Galt Ph.D

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New techniques, distinctive population, unique normal databases

Received Mar New techniques, distinctive population, unique normal databases James R. Galt 0 2 Ph.D 0 1 2 0 Reprint requests: James R. Galt, Ph.D., Department of Radiology and Imaging Sciences, Emory University Hospital , 1364 Clifton Road, Atlanta, Georgia 30322 , USA 1 Department of Radiology and Imaging Sciences, Emory University School of Medicine , Atlanta , Georgia 2 Galt New techniques , distinctive population - No charge is more important to nuclear cardiology than that of efficiently providing accurate results at low radiation doses. Keeping the radiation dose low requires that we do a better job of detecting photons emitted from the myocardium and do a better job of utilizing each photon we detect. This quest has drastically increased the diversity of reconstruction techniques and instrumentation for SPECT myocardial perfusion imaging. Each reconstruction technique produces images with its own unique texture. Each novel device introduces new considerations for the technologist acquiring the scan and new considerations for the clinician interpreting the images including unique patterns of normal and unique artifacts. When quantitative analysis is performed, normal databases developed with standard equipment and techniques may no longer be appropriate.1,2 The study that inspired this editorial details the construction of 201Tl normal databases for one of one such system, IQ SPECT, in a distinctive population (Japan).3 HIGH-SENSITIVITY SPECT Several methods have been developed to shorten acquisition time, to allow a reduction in injected radiopharmaceutical dose or a trade-off between the two. Originally developed to provide short scan times, advanced reconstruction methods seek to do a better job of producing SPECT images with the counts acquired by the imaging system than filtered backprojection or standard iterative reconstruction methods. As the improvements work with conventional SPECT systems, they can be thought of as providing an effective increase in photon sensitivity. These algorithms model the acquisition process including the geometric response of the collimator (sometimes called resolution recovery) and use unique noise reduction algorithms to produce high-quality images with a substantial reduction in acquired counts.4,5 Other systems have increased photon sensitivity through the use of high-sensitivity collimation and multiple detectors to perform a cardio-centric acquisition. Regardless of the collimation used, each system also takes advantage of advanced SPECT reconstruction algorithms to further improve the sensitivity of the system.5,6 One such system uses three pixelated cesium iodide scintillation detectors and fan-beam collimation to increase sensitivity of counts collected from the heart (Cardius X-ACT, Digirad, Poway, CA). In this system, the patient sits upright in a chair that rotates. During acquisition, the heart of a properly set-up patient remains in the center of each of the fan-beam collimators, maximizing counts from the heart. Two other systems utilize direct-conversion solidstate detectors made of Cadmium Zinc Telluride (CZT) but very different collimation schemes. The first CZT system uses nine rectangular detectors with very highsensitivity parallel-hole collimation that sweep across the heart of the patient (D-SPECT Spectrum Dynamics, Caesarea, Israel). Counts from the heart are maximized by confining the sweep of each detector to the region of the heart. The second CZT system uses 19 square CZT detectors each equipped with a single pinhole collimator (GE Healthcare, Haifa, Israel). The center line of each detector passes through the same point in space. With this system the detectors and the patient remain stationary during acquisition and the heart of a properly positioned patient is centered on the point where the center lines of all the pinhole collimators meet. The system used in the paper by Okuda achieves high sensitivity using a unique collimator design on a standard, large field of view, dual detector SPECT or SPECT/CT system (IQ SPECT, Siemens, Erlangen, Germany).3 The confocal collimators used in IQ SPECT have a central area with converging collimation designed to focus on the heart and transition to parallel-hole collimation around the periphery of the camera. This design allows increased sensitivity over the heart where it is most needed but avoids truncation of the body.7 It is important that the heart be properly positioned in the region of highest magnification of both collimators throughout acquisition. While slight mispositioning may be tolerable, poor patient set-up may be less forgiving than standard parallel-hole collimation.8,9 It has also been noted that attenuation artifacts may differ from those routinely recognized with standard parallel-hole collimation and that attenuation corrected images may be preferred.9 The use of IQ SPECT to reduce imaging time and/ or radiopharmaceutical dose has been demonstrated in phantoms and in patients.7,10 In one study based on patient images, Lyon et al compared attenuation corrected stress SPECT to IQ SPECT using a dose of 9251100 MBq (25-30 mCi) Tc-99m sestamibi. Several different count levels were simulated for IQ SPECT, and evaluated using system and count level specific normal files. The study concluded that IQ SPECT could be used to reduce both the dose and the time by half compared to conventional SPECT. Thus, the standard dose could be reduced to below 550 MBq (15 mCi) and the imaging time reduced from 13 minutes (standard SPECT) to 7 minutes (IQ SPECT).10 While the three high-sensitivity hardware designs discussed above are dedicated cardiac cameras, only when the confocal collimator is mounted is the system restricted to nuclear cardiology. When equipped with other collimators, the system is a general purpose SPECT or SPECT/CT, a factor that may appeal to clinics that also perform general nuclear medicine imaging studies. NORMAL DATABASES Nuclear cardiology professionals, both technologists and physicians, can expect a significant learning curve when switching to high-sensitivity SPECT. Patient setup is not only different for the technologist but can be much less forgiving of error when the cameras and collimation need to focus on the heart. Physicians may find that images may have unfamiliar texture, and clues to separating artifacts from normality, such as normal attenuation patterns, may also differ. Properly implemented, quantitative analysis software that compares each scan with normal databases can not only serve as tool to help with diagnoses but may also help a physician become comfortable with an unfamiliar system. This only holds true, however, if normal databases for your SPECT system, reconstruction software, radiopharmaceutical, and patient demographics are available.1,11–15 When quantitative comparison to normal databases is applied, normal databases need to match the imaging system, the radiopharmaceutical, the reconstruction techniques, and the patient population. The Japanese Society of Nuclear Medicine working group (JSNM-WG) has worked to standardize techniques and has developed databases for the Japanese population using conventional SPECT systems.16–18 A comparison of the Japanese normal databases to a US database generated with conventional SPECT found significant differences. The authors concluded that not only was an acquisition specific database essential but it was essential to use population-specific databases as well. The authors also speculated that the differences might have been due to differences in body habitus, rather than ethnicity. BMIs reported in that paper were 22 ± 3 and 24 ± 3 for the Japanese database and 27 ± 5 for the US database.19 Extrapolation of from Okuda Table one 3 indicates the average BMI in the Japanese IQ SPECT database would be similar or smaller than those of the Japanese standard database. 201TL IQ SPECT IN JAPAN The use of IQ SPECT with 201Tl in a Japanese population has been reported previously. Horiguchi et al showed that, compared to standard acquisition of 20 minutes, that image quality and semi-quantitative analysis of IQ SPECT with an acquisition of 8 minutes yielded comparable results, especially when CTAC was used.20 Takamura et al investigated the use of prone imaging with IQ SPECT, finding that prone imaging provided similar benefits for avoiding artifacts as CTAC. Acquisition times were 8 minutes.21 Matsuo et al compared IQ SPECT acquisitions of 6 minutes with a standard acquisition of 20 minutes finding that the images were of equivalent quality. They noted that CTAC improved inferior artifacts with some apparent decrease in anterior or apical anterior segments.22 Standard doses set by the Japanese working group for Tl-201 are 74-111 MBq (2-3 mCi), which is used in about half of the SPECT MPI studies as of 2015 due to its high extraction fraction, defect contrast, image quality, and the use of a single administration for both stress and rest.18 Each of the studies at total of 111 MBq (3 mCi) 201Tl was used. Horiguchi and Takamura injected the full dose at stress and performed delayed imaging at 3 hours. The delayed images were used in their investigations. Matsuo injected 74 MBq (2 mCi) at stress. Resting images were acquired 2–3 hours after an additional injection of 37 mBq (1 mCi). Use of 201Tl at these doses makes it difficult to meet the goal of an effective radiation dose of B9 mSv given in the ASNC Information Statement on Recommendations for Reducing Radiation Exposure in Myocardial Perfusion Imaging.23 Using an estimate of 4.4 mSv per mCi (37 mBq)24 74 MBq yields 8.8 mSv. Increasing the dose to 111 mBq yields 13.2 mSv. Adding a CT dose of up to 2.5 mSv for attenuation correction10 pushes the total dose well over the 9 mSv limit. Assuming that use of 201Tl myocardial SPECT will continue and that IQ SPECT is used at a significant number of imaging centers, the uniqueness of the collimation, the radiopharmaceutical used, and the patient demographics made the development of new normal databases necessary. Okuda et al set out to develop these databases for various protocols: rest and stress acquisitions for supine, prone, and ACSC. This work was done with retrospective data and without rigorous standardization.3 Ideally, this would be done prospectively with standard acquisition protocols but sometimes you have to work with the data you have. The significant differences between the IQ SPECT normal databases developed for the different acquisition protocols illustrate the need for the separate databases. The normal databases developed for confocal collimation and the unique reconstruction differ significantly different from those developed for conventional SPECT (as well as the differences between the male and female normal files—or the lack of difference with ACSC). Others, including this editorialist, have found that when attenuation correction is applied, a combined normal database may be used for male and female patients.25,26 The use of new high-sensitivity SPECT comes at the cost of images that are different from those that familiar to the clinician. At the same time, application of quantitative software to these images requires the development of new normal databases. In the US, most users are accustomed to receiving appropriate databases with the purchase of quantitative software. Those databases may not be available with the introduction of new imaging equipment, new radiopharmaceuticals, or as old radiopharmaceuticals (201Tl) fall out-of-favor. James R. Galt has no disclosures related to this editorial. In areas of the world with a population that differs in body habitus from that developed for the US, the need may be even greater. The bottom line is that the benefits of quantitative software come at the cost of normal database development for different imaging systems, reconstruction techniques, radiopharmaceuticals, and patient populations. 1. Zoccarato O , Marcassa C , Lizio D , Leva L , Lucignani G , Savi A , et al. Differences in polar-map patterns using the novel technologies for myocardial perfusion imaging . J Nucl Cardiol 2016 . doi:10.1007/s12350- 016 - 0500 -9. 2. Slomka PJ , Rubeaux M , Germano G . Quantification with normal limits: New cameras and low-dose imaging . J Nucl Cardiol 2016 . doi:10.1007/s12350- 016 - 0563 -7. 3. Okuda K , Nakajima K , Matsuo S , Kondo C , Sarai M , Horiguchi Y , et al. Creation and characterization of normal myocardial perfusion imaging databases using the IQ SPECT system . J Nucl Cardiol 2017 . doi:10.1007/s12350- 016 - 0770 -2. 4. Gordon DePuey E 3rd. Advances in cardiac processing software . Semin Nucl Med 2014 ; 44 : 252 - 73 . doi: 10.1053/j.semnuclmed. 2014 .04.001. 5. Piccinelli M , Garcia EV . Advances in single-photon emission computed tomography hardware and software . Cardiol Clin 2016 ; 34 : 1 - 11 . doi:10.1016/j.ccl. 2015 .06.001. 6. Slomka PJ , Berman DS , Germano G. New cardiac cameras: single-photon emission CT and PET . Semin Nucl Med 2014 ; 44 : 232 - 51 . 7. Caobelli F , Kaiser SR , Thackeray JT , Bengel FM , Chieregato M , Soffientini A , et al. IQ SPECT allows a significant reduction in administered dose and acquisition time for myocardial perfusion imaging: evidence from a phantom study . J Nucl Med 2014 ; 55 : 2064 - 70 . 8. Caobelli F , Ren Kaiser S , Thackeray JT , Bengel FM , Chieregato M , Soffientini A , et al. The importance of a correct positioning of the heart using IQ-SPECT system with multifocal collimators in myocardial perfusion imaging: A phantom study . J Nucl Cardiol 2015 ; 22 : 57 - 65 . 9. Gremillet E , Agostini D. How to use cardiac IQ SPECT routinely? An overview of tips and tricks from practical experience to the literature . Eur J Nucl Med Mol Imaging 2016 ; 43 : 707 - 10 . 10. Lyon MC , Foster C , Ding X , Dorbala S , Spence D , Bhattacharya M , et al. Dose reduction in half-time myocardial perfusion SPECT-CT with multifocal collimation . J Nucl Cardiol 2016 ; 23 : 657 - 67 . 11. Slomka PJ , Rubeaux M , Germano G . Quantification with normal limits: New cameras and low-dose imaging . J Nucl Cardiol 2016 . doi:10.1007/s12350- 016 - 0563 -7. 12. Miao TL , Kansal V , Glenn Wells R , Ali I , Ruddy TD , Chow BJ . Adopting new gamma cameras and reconstruction algorithms: Do we need to re-establish normal reference values ? J Nucl Cardiol 2016 ; 23 : 807 - 17 . 13. DePuey EG . Sources of variability of gated myocardial perfusion SPECT quantitative parameters . J Nucl Cardiol 2016 ; 23 : 818 - 23 . 14. Alexiou S , Georgoulias P , Angelidis G , Valotassiou V , Tsougos I , Psimadas D , et al. Myocardial perfusion and left ventricular quantitative parameters obtained using gated myocardial SPECT: Comparison of three software packages . J Nucl Cardiol 2016 . doi: 10.1007/s12350- 016 - 0730 -x. 15. Germano G . Quantitative measurements of myocardial perfusion and function from SPECT (and PET) studies depend on the method used to perform those measurements . J Nucl Cardiol 2016 . doi:10.1007/s12350- 016 - 0757 -z. 16. Nakajima K , Matsuo S , Kawano M , Matsumoto N , Hashimoto J , Yoshinaga K , et al. The validity of multi-center common normal database for identifying myocardial ischemia: Japanese Society of Nuclear Medicine working group database . Ann Nucl Med 2010 ; 24 : 99 - 105 . 17. Nakajima K. Normal values for nuclear cardiology: Japanese databases for myocardial perfusion, fatty acid and sympathetic imaging and left ventricular function . Ann Nucl Med 2010 ; 24 : 125 - 35 . 18. Nakajima K , Matsumoto N , Kasai T , Matsuo S , Kiso K , Okuda K. Normal values and standardization of parameters in nuclear cardiology: Japanese Society of Nuclear Medicine working group database . Ann Nucl Med 2016 ; 30 : 188 - 99 . 19. Nakajima K , Okuda K , Kawano M , Matsuo S , Slomka P , Germano G , et al. The importance of population-specific normal database for quantification of myocardial ischemia: Comparison between Japanese 360 and 180-degree databases and a US database . J Nucl Cardiol 2009 ; 16 : 422 - 30 . 20. Horiguchi Y , Ueda T , Shiomori T , Kanna M , Matsushita H , Kawaminami T , et al. Validation of a short-scan-time imaging protocol for thallium-201 myocardial SPECT with a multifocal collimator . Ann Nucl Med 2014 ; 28 : 707 - 15 . 21. Takamura T , Horiguchi Y , Kanna M , Matsushita H , Sudo Y , Kikuchi S , et al. Validation of prone myocardial perfusion SPECT with a variable-focus collimator versus supine myocardial perfusion SPECT with or without computed tomography-derived attenuation correction . Ann Nucl Med 2015 ; 29 : 890 - 6 . 22. Matsuo S , Nakajima K , Onoguchi M , Wakabayash H , Okuda K , Kinuya S. Nuclear myocardial perfusion imaging using thallium201 with a novel multifocal collimator SPECT/CT: IQ-SPECT versus conventional protocols in normal subjects . Ann Nucl Med 2015 ; 29 : 452 - 9 . 23. 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 . 24. Henzlova MJ , Duvall WL , Einstein AJ , Travin MI , Verberne HJ . ASNC imaging guidelines for SPECT nuclear cardiology procedures: Stress, protocols, and tracers . J Nucl Cardiol 2016 ; 23 ( 3 ): 606 - 39 . 25. Grossman GB , Garcia EV , Bateman TM , Heller GV , Johnson LL , Folks RD , et al. Quantitative Tc-99m sestamibi attenuation-corrected SPECT: Development and multicenter trial validation of myocardial perfusion stress gender-independent normal database in an obese population . J Nucl Cardiol 2004 ; 11 : 263 - 72 . 26. Esteves FP , Galt JR , Folks RD , Verdes L , Garcia EV . Diagnostic performance of low-dose rest/stress Tc-99m tetrofosmin myocardial perfusion SPECT using the 530c CZT camera: quantitative vs visual analysis . 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James R. Galt Ph.D. New techniques, distinctive population, unique normal databases, Journal of Nuclear Cardiology, 2017, 1-4, DOI: 10.1007/s12350-017-0876-1