Update in Nuclear Cardiology: Patient-Centered Imaging Radiation Dose Reduction

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1 Update in Nuclear Cardiology: Patient-Centered Imaging Radiation Dose Reduction E. Gordon DePuey, M.D. Icahn School of Medicine ant Mt. Sinai New York, NY Disclosures: Grant Support: Michael J. Fox Foundation Consultant: Adenosine Therapeutics, Cardinal Health

2 Patient-Centered Imaging The goal of the ASNC Preferred Practice Statement is to help providers choose the proper imaging procedure for the individual patient One MPI test DOES NOT fit all DePuey EG, Miller TD, Mahmarian JJ et al, JNC 2012

3 Patient-Centered Imaging Combines aspects of: Safety Risk of additional inappropriate testing and or therapies if imaging sub-optimally performed Limitation of radiation exposure in younger/female patients Clinical utility Choosing the correct technique and/or protocol to answer the clinical question Cost Convenience Patient Satisfaction

4 ASNC Initiatives to Decrease Patient Radiation Exposure Promote awareness of radiation exposure associated with various MPI imaging protocols Encourage adherence to MPI Appropriate Use Criteria

5 Appropriate Use Criteria for Cardiac Radionuclide Imaging: Guidelines Relevant to Decreasing Patient Radiation Exposure Minimize scans in low-likelihood patients with interpretable ECGs and in asymptomatic non-diabetic patients Decrease follow-up scans in patients with initially normal scans (with no change in symptoms) Delay/decrease scans in patients S/P PCI and CABG Hendel RC et al, J Am Coll Cardiol 2009;53:

6 ASNC Initiatives to Decrease Patient Radiation Exposure Promote awareness of radiation exposure associated with various MPI imaging protocols Encourage adherence to MPI Appropriate Use Criteria Set a goal to reduce radiation exposure by 2014

7 Patient Radiation Exposure Associated with SPECT and PET MPI Protocols PROTOCOLS EDE (msv) One-Day Tc-99m Rest/Stress or Stress/Rest Protocol Two-Day Stress/Rest or Rest/Stress Tc99m Protocol Stress-Only Tc-99m Protocol One-Day Rest Tl-201/Stress Tc-99m Dual Isotope Protocol 29.2 One-Day Tl-201 Stress/Redistribution Protocol 22.0 One-Day Tl-201 Stress/Re-injection/Redistribution Protocol 31.4 Rest/Stress Rubidium-82 (PET/CT) Rest/Stress N-13 Ammonia (PET/CT) 1.5

8 Recommendations for Reducing Radiation Exposure in Myocardial Perfusion Imaging: ASNC Information Statement Decrease MPI radiation dose to <9mSv in 50% of patients by 2014 Cerqueria MD et al. J Nucl Cardiol, May 2010

9 ASNC Patient-Centered Imaging Document DePuey EG, Miller TD, Mahmarian JJ et al, JNC 2012 Encourage stress-only imaging in low-intermediate likelihood patients

10 *No prior MI, no known CAD, no prior revascularization, no CHF, not high-likelihood of CAD Stress-Only Tc-99m Protocol In a recent ASNC information statement, stress-only imaging was recommended when applied to properly selected patients*. In order to perform stress-only imaging, either a one-day or two-day stressrest Tc-99m imaging protocol must be used. The choice of imaging protocol will depend on patient body weight and habitus. Two large trials evaluating over 21,000 patients with a normal SPECT study have demonstrated the safety of stress-only imaging as compared to traditional stress/rest imaging. - Comparably low all-cause and cardiac mortality rates were observed with both imaging protocols. This was true irrespective of patient age, gender, cardiac risk factor profile or stressor employed with SPECT. These results are consistent with earlier studies evaluating patient outcome following normal stress-only imaging. - The stress Tc-99m imaging procedure is identical to that described above. Chang SM, Nabi F, Xu J, Raza U, Mahmarian JJ. Normal stress-only versus standard stress/rest myocardial perfusion imaging: similar patient mortality with reduced radiation exposure. J Am Coll Cardiol 2010;55: Duvall WL, Wijetunga MN, Klein TM, et al. The prognosis of a normal stress-only Tc-99m myocardial perfusion imaging study. J Nucl Cardiol 2010;17: Gibson PB, Demus D, Noto R, Hudson W, Johnson LL. Low event rate for stress-only perfusion imaging in patients evaluated for chest pain. J Am Coll Cardiol 2002;39: Gal R, Ahmad M. Cost-saving approach to normal technetium-99m sestamibi myocardial perfusion scan. Am J Cardol 1996;78:

11 Stress-Only Tc-99m Protocol Advantages Patient convenience/satisfaction and laboratory efficiency are improved. There is a marked reduction in patient radiation exposure by eliminating the higher rest Tc-99m dose. In one recent study, the mean Tc-99m dose was significantly lower at 21.3±10.7 mci with stress-only vs. 55.1±11.9 mci with stress/rest imaging. This was particularly true for patients who received an initial low dose of Tc-99m as part of a same day stress/rest protocol (13.5±2 mci). 5 Conservation of Tc-99m radiopharmaceuticals Reduced cost by eliminating injection of a second Tc-99m dose and the subsequent rest imaging

12 Stress-Only Tc-99m Protocol Disadvantages There are no specific disadvantages to a stress-only imaging approach. When properly utilized a normal stress-only study predicts the same excellent prognosis as compared to standard stress/rest imaging. However, there are specific issues that need to be considered prior to implementing stress-only imaging in an individual laboratory: First, there is a requirement to assess each patient on arrival to the laboratory to choose the most appropriate imaging protocol rather than a Differentiation of artifact from a true perfusion abnormality is more difficult without a resting scan and therefore requires the expertise of an experienced reader. In this regard, attenuation correction with either x-ray computed tomography (CT) or line sources may be advantageous if a stress-only protocol is used. Recent data indicate that a stress-only imaging protocol coupled with attenuation correction techniques can be effectively applied to obese patients where a normal study predicts an excellent outcome. Prone imaging can also be used to clarify inferior perfusion defects due to diaphragmatic attenuation observed on supine images. The perfusion images should be unequivocally normal by visual and, preferably, quantitative analysis - and LV cavity size, LVEF and regional wall motion and thickening should be normal.

13 ASNC Patient-Centered Imaging Document Encourage stress-only imaging in low-intermediate likelihood patients Encourage increased SPECT acquisition time, as tolerated by patients, in preference to weight-base dosing in large patients DePuey EG, Miller TD, Mahmarian JJ et al, JNC 2012

14 Modification of SPECT Acquisition Time to Yield Adequate Myocardial Count Density Unique Count-Based SPECT ACQ Consistent inter-patient data integrity Automated ACQ Technique that ensures ASNC Quality Standards At least 60 or 64 projections at 44, 000 counts At least 30 0r 32 projections at 20,000 counts 22,000 counts in the heart, stress LAO 10,000 counts in the heart, rest LAO Easy Positioning Cardiocentric patient positioning tool TruACQ CBI Clinical Benefit Consistent High Image quality Increased Physician Confidence Repeatable Quality Regardless of body habitus Decreased likelihood of low count density artifacts Incidental benefit to monitor patient motion during acquisition NOTE: Myocardial count rate determined from user defined regions of interest for the three detector heads. Digirad TruACQ, Courtesy Digirad Corp.

15 ASNC Patient-Centered Imaging Document Encourage stress-only imaging in low-intermediate likelihood patients Encourage increased SPECT acquisition time, as tolerated by patients, in preference to weight-base dosing in large patients Discourage dual-isotope and stress/delayed Tl-201 protocols DePuey EG, Miller TD, Mahmarian JJ et al, JNC 2012

16 Patient Radiation Exposure Associated with SPECT and PET MPI Protocols PROTOCOLS EDE (msv) One-Day Tc-99m Rest/Stress or Stress/Rest Protocol Two-Day Stress/Rest or Rest/Stress Tc99m Protocol Stress-Only Tc-99m Protocol One-Day Rest Tl-201/Stress Tc-99m Dual Isotope Protocol 29.2 One-Day Tl-201 Stress/Redistribution Protocol 22.0 One-Day Tl-201 Stress/Re-injection/Redistribution Protocol 31.4 Rest/Stress Rubidium-82 (PET/CT) Rest/Stress N-13 Ammonia (PET/CT) 1.5

17 ASNC Patient-Centered Imaging Document Encourage stress-only imaging in low-intermediate likelihood patients Encourage increased SPECT acquisition time, as tolerated by patients, in preference to weight-base dosing in large patients Discourage dual-isotope and stress/delayed Tl-201 protocols Utilize new reduced count-density software and new solid-state camera technology to decrease injected activity DePuey EG, Miller TD, Mahmarian JJ et al, JNC 2012

18 Hardware and Software Advancements to Accommodate Lower Cardiac Counting Statistics Cardio-focused collimation Parallel hole collimator with central converging collimation Multiple scanning parallel hole collimators Multi-pinhole collimators

19 Cardio-Focused Collimation

20 Hardware and Software Advancements to Accommodate Lower Cardiac Counting Statistics Cardio-focused collimation Parallel hole collimator with central converging collimation Multiple scanning parallel hole collimators Multi-pinhole collimators Solid state CsI and CZT detectors

21 Semiconductor Detectors: CsI and C Z T Smaller Detector Size: Thus Smaller Cameras and Variable Detector Geometry Standard photomultiplier tube (left) Solid state detector (CZT) (right) 4 cm

22 Advantages of Semi-Conductor Detectors vs. Sodium Iodide Scored detector size defines spatial resolution, obviating time-consuming positioning circuitry Higher count rates Improved spatial resolution Direct conversion of incident photon to electrical signal Higher count rates Improved energy resolution Lower maintenance Stationary gantry Semiconductor detectors resistant to physical damage and hydration semiconductor elements sometimes occur)

23 Spatial Response Comparison Direct digital positioning provides for excellent intrinsic spatial resolution and enhanced image contrast. Relative Response Scintillation Camera Y mm X mm

24 2D Full Stress (6.7 min) vs. 3D Half (3.3 min), Triple Head 2D Full 3D Half 2D Full 3D Half 2D Full 3D Half nspe E D, Digirad, Inc. Maddahi, J. et al; JNM 2008, 49 (1): 2P

25 Low Dose Tc-99m Protocol CZT Solid State Detectors with Cardio-focused Parallel-hole Collimation STR 3.5mCi - 12min RST 8.0mCi - 5min BMI = 28.3

26 Hardware and Software Advancements to Accommodate Lower Cardiac Counting Statistics Cardio-focused collimation Parallel hole collimator with central converging collimation Multiple scanning parallel hole collimators Multi-pinhole collimators Solid state CsI and CZT detectors Software to cope with lower counting statistics

27 Software Solutions: Preservation of SPECT Image Quality Despite Lower Counting Statistics Iterative Reconstruction Resolution Recovery Noise Reduction

28 Full-time OSE M Half-time W BR

29 Full-time OSE M Quarter-time Xpress-

30 Quarter-time WBR

31 Half-Dose MPI SPECT A full-dose/half-time acquisition or A half-dose/full-time acquisition both yield 1/2 the standard counting statistics

32 Half-dose R/S (7.3/17.5 mci) Tc-99m sestamibi WBR 63 y.o. male HTN, cholesterol Prior PCI Fixed inferoapical defect c/w scar

33 Patient Radiation Dose (EDE): Advantages of Reduced-Dose Protocols Full-Dose Protocol Tc-99m tetrofosmin R/S SPECT = 8.6 msv Tc-99m sestamibi R/S SPECT = 10.7 msv Half-Dose Protocol Tc-99m tetrofosmin R/S SPECT = 4.3 msv Tc-99m sestamibi R/S SPECT = 5.4 msv Half-Dose Stress-Only Protocol* Tc-99m sestamibi S SPECT = 1.4 msv *Note: stress-only protocols should be used only in patients with no prior MI, normal LV function, and a low-intermediate likelihood of CAD

34 Patient-Specific Examples

35 The Asymptomatic Patient In asymptomatic patients without known CAD, appropriateness of MPI is dependent on ATP III risk and/or coronary artery calcium score (CACS). Appropriate indications include High ATP III risk Mod/High ATP III risk and CACS = 25% of MPI abnormal, or CACS >400 = 40% abnormal In asymptomatic patients with known CAD, appropriate MPI indications include: Known incomplete revascularization Prior CABG > 5 years ago Recommendations: General Exercise stress preferred Reduces splanchnic activity, minimizes attenuation Tc-99m tracers used to lower radiation and improve quality No known CAD: -- imaging if possible Known CAD: Single day rest/stress or 2- day stress/rest protocol Minimizes potential underestimation of ischemia

36 Very low-dose Stress/High-dose Stress Wide Beam ReconstructionTc-99m sestamibi SPECT 5.2 mci stress 12-min SPECT

37 The Symptomatic Patient with Suspected CAD Appropriate in patients with unexplained chest pain or symptoms suggestive of ischemia 50-60% of symptomatic patients will have normal imaging and low event rates Recommendations: Stress-first (potentially stress-only) imaging Can be performed in > 25% of all patients referred for MPI Reduces radiation exposure Reduced-dose MPI with new software and/or instrumentation

38 Very low-dose Stress/High-dose Stress Wide Beam ReconstructionTc-99m sestamibi SPECT 5.2 mci stress 36.2 mci rest 12-min SPECT DePuey et al 2012 SNM Annual Meeting

39 The Symptomatic Patient with Known CAD MPI provides valuable diagnostic and prognostic information in patients with known CAD Normal Study=low event rate Recommendations: Focus on optimizing sensitivity of test for detection of ischemia Rest/Stress Tc-99m or 2-day protocol Radiation exposure less of a concern

40 63 yo man with prior IWMI, on medical management, with back pain and recurrent angina Discovery 530c CZT solid state camera 8/24 mci Tc-99m sestamibi; 2-minute stress, 4-minute rest acquisitions

41 ASNC Patient-Centered Imaging Document Encourage stress-only imaging in low-intermediate likelihood patients Encourage increased SPECT acquisition time, as tolerated by patients, in preference to weight-base dosing in large patients Discourage dual-isotope and stress/delayed Tl-201 protocols Utilize new reduced count-density software and new solid-state camera technology to decrease injected activity Consider Rb-82 and N-13 ammonia PET as an alternative to SPECT to lower radiation dose DePuey EG, Miller TD, Mahmarian JJ et al, JNC 2012

42 Rest/Stress Rubidium-82 Advantages Rapidity of the protocol (30-45 minutes). Relatively low radiation exposure ( msv, depending on PET scanner) Accurate attenuation correction. Quantification of myocardial blood flow reserve using recently FDA-approved commercial software applications. These advantages make Rb-82 PET a more sensitive and specific imaging technique for the diagnosis of ischemia Rb-82 PET is also optimal in patients who require rapid imaging, patients in whom there are radiation exposure concerns (younger patients), and in obese patients in whom attenuation artifacts are anticipated.

43 Rb-82 PET: LCx Ischemia

44 Rest/Stress Rubidium-82 Disadvantages Image quality usually no better than high quality Tc- 99m SPECT Limited availability of PET/CT equipment Relatively high procedural cost per study Rb-82 generator, presently requiring 5-6 scans/day to break even Limited prognostic data as compared to SPECT Requirement for pharmacological stress Limited reimbursement Medicare Program Payment Policies Under the Physician Fee Schedule and Other Revisions to Part B for CY2011, 75 Federal Register (2010).

45 Rest/Stress N-13 Ammonia Advantages Superior image quality due to lower energy positron Rapid study acquisition (less then one hour) Very low radiation exposure (1.5 msv effective dose for 10.0 mci rest and stress dose) Accurate CT attenuation correction Allows calculation of a peak stress LVEF Quantification of myocardial blood flow reserve using recently FDA-approved commercial software applications Provides superior image quality and more accurately tracks peak hyperemic myocardial blood flow than Rb-82 (higher energy positron) Can be performed with exercise in selected patients due to its longer half-life

46 Myocardial Blood Flow Reserve: Assessment with N-13 Ammonia PET A. Angiographic stenosis >50% + MPI ischemic perfusion defect(s) B. Angiographic stenosis >50% + No MPI ischemic perfusion defect(s) C. Angiographic stenosis <50% + No MPI ischemic perfusion defect(s) Nkoulou R et al. J Nucl Med 2009;50;1170

47 Rest/Stress N-13 Ammonia Disadvantages Limited availability of PET equipment. Relatively high procedural cost per study Limited prognostic data as compared to SPECT. Limited availability of N-13 ammonia due to its relatively short half-life (10 minutes) and the requirement for an on-site cyclotron or delivery from a nearby facility with a cyclotron.

48 Summary and Conclusions Patient-centered imaging will improve the diagnostic and prognostic performance of MPI and reduce patient radiation exposure. ASNC recommends MPI imaging protocols be tailored to individual patients

49 THANK YOU