Measuring SPECT myocardial blood flow at the University of Ottawa Heart Institute.

The introduction of new cardiac SPECT cameras has made it practical to do dynamic SPECT imaging and opened the door to performing myocardial blood flow (MBF) imaging with SPECT. In this paper, we describe in detail our approach to dynamic SPECT MBF imaging using a multi-pinhole cardiac SPECT camera and commercially available kinetic analysis software. We use a 1-day rest/stress protocol with 370 MBq injected at rest and 1,000 MBq at stress with a 1- to 2-hour interval between rest and stress imaging. The tracer is injected mechanically over 30 seconds using a syringe pump. Projection data are acquired in listmode for a duration of 11 minutes and then reframed into a dynamic series. Each image is reconstructed independently using vendor-supplied software. The dynamic images are corrected for residual activity and manually corrected for motion using rigid-body translation. The uptake rate constant, K1, is calculated using a 1-tissue-compartment kinetic model and converted to MBF using a previously determined extraction fraction correction.

Strategies for Minimizing Occupational Radiation Exposure in Cardiac Imaging.

PURPOSE OF REVIEW: Radiation safety has been at the center of interest of both researchers and healthcare institutions. This review will summarize and shed light on the various techniques adapted to reduce staff exposure to ionizing radiation (IR) in the field of cardiac imaging. RECENT FINDINGS: In the last years, with the advance of awareness and the development of new technologies, there have been several tools and techniques adapted. The breakthrough of several technologies to lower radiation dose and shorten the duration of diagnostic tests associated with IR, the use of protection devices by staff members, and mostly the awareness of exposure to IR are the hallmark of these advances. Using all these measures has led to a significant decrease in staff exposure to IR. Reducing staff exposure to meet the "As Low As Reasonably Achievable" principle is feasible. This review introduces the most important strategies applied in cardiac imaging.

Planar radionuclide angiography with a dedicated cardiac SPECT camera.

BACKGROUND: We compared a dedicated cardiac camera with a traditional system for left ventricular (LV) functional measurements using gated blood-pool imaging. METHODS: 24-frame gated planar images were obtained from 48 patients in an LAO orientation for 6M counts/view on a standard gamma camera. Immediately thereafter, 24-frame ECG-gated data were obtained for 8 minutes on a dedicated cardiac SPECT camera. The gated SPECT image volumes were iteratively reconstructed and then transferred offline. In-house software was used to reproject the images into a 24-frame gated planar format. Both the original and the reprojected gated planar datasets were analyzed using semiautomated software to determine ejection fraction (EF), ventricular volume (end diastolic volume, EDV), peak ejection rate (PER), and peak filling rate (PFR). RESULTS: The difference in EF values averaged 0.4% ± 4.4%. The correlation in EF was r ≥ 0.94 (P < .01) with a linear regression slope of 0.98. Correlation of the EDV was r ≥ 0.86 (P < .01), but the volumes from the dedicated cardiac camera were smaller (linear regression slope was 0.6). Correlation of PFR and PER were r = 0.91 and r ≥ 0.83, respectively (P < .01 for both). CONCLUSIONS: Reprojection of 24-frame gated blood-pool SPECT images is an effective means of obtaining LV functional measurements with a dedicated cardiac SPECT camera using standard 2D-planar analysis tools.

Test-Retest Precision of Myocardial Blood Flow Measurements With 99mTc-Tetrofosmin and Solid-State Detector Single Photon Emission Computed Tomography.

BACKGROUND: Measurement of myocardial blood flow (MBF) with single photon emission computed tomography (SPECT) is feasible using cardiac cameras with solid-state detectors. SPECT MBF has been shown to be accurate when compared with positron emission tomography MBF measured in the same patients. However, the value of a test result applied to an individual patient depends strongly on the precision or repeatability of the test. The purpose of our study is to measure the precision of SPECT MBF measurements using 99mTc-tetrofosmin and a solid-state cardiac camera. METHODS: SPECT MBF was measured in 30 patients and repeated at a mean interval of 18 days. MBF was evaluated from images with and without attenuation correction based on a separately acquired CT scan. The dynamic images were processed independently by 2 operators using in-house kinetic analysis software that applied a 1-tissue-compartment model. The K1 rate constant was converted to MBF using previously determined extraction fraction corrections. Correction for patient body motion was applied manually. RESULTS: The average coefficient of variation (COV) in the differences between the 2 MBF measurements was between 28% and 31%. The interobserver COV was between 11% and 15%. Myocardial flow reserve is the ratio of MBF measured at stress and rest, and the COV is correspondingly higher. The COV for the difference in repeated myocardial flow reserve was 33% to 38%, whereas the interobserver COV was 13% to 22%. CONCLUSIONS: The COV for the difference in SPECT MBF measurements obtained on separate days is 28% to 31%. The corresponding COV for myocardial flow reserve is 33% to 38%.

Optimization of SPECT Measurement of Myocardial Blood Flow with Corrections for Attenuation, Motion, and Blood Binding Compared with PET.

Myocardial blood flow (MBF) and myocardial flow reserve (MFR) measured with PET have clinical value. SPECT cameras with solid-state detectors can obtain dynamic images for measurement of MBF and MFR. In this study, SPECT measurements of MBF made using 99mTc-tetrofosmin were compared with PET in the same patients. Methods: Thirty-one patients underwent PET MBF rest-stress studies performed with 82Rb or 13N-ammonia within 1 mo of their SPECT study. Dynamic rest-stress measurements were made using a SPECT camera. Kinetic parameters were calculated using a 1-tissue-compartment model and converted to MBF and MFR. Processing with and without corrections for attenuation (+AC and -AC), patient body motion (+MC and -MC), and binding of the tracer to red blood cells (+BB and -BB) was evaluated. Results: Both +BB and +MC improved the accuracy and precision of global SPECT MBF compared with PET MBF, resulting in an average difference of 0.06 ± 0.37 mL/min/g. Global MBF and detection of abnormal MFR were not significantly improved with +AC. Global SPECT MFR with +MC and +BB had an area under the receiver-operating curve of 0.90 (+AC) to 0.95 (-AC) for detecting abnormal PET MFR less than 2.0. Regional analysis produced similar results with an area under the receiver-operating curve of 0.84 (+AC) to 0.87 (-AC). Conclusion: Solid-state SPECT provides global MBF and MFR measurements that differ from PET by 2% ± 32% (MBF) and 2% ± 28% (MFR).

Reduced dose measurement of absolute myocardial blood flow using dynamic SPECT imaging in a porcine model.

PURPOSE: Absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) measurements provide important additional information over traditional relative perfusion imaging. Recent advances in camera technology have made this possible with single-photon emission tomography (SPECT). Low dose protocols are desirable to reduce the patient radiation risk; however, increased noise may reduce the accuracy of MBF measurements. The authors studied the effect of reducing dose on the accuracy of dynamic SPECT MBF measurements. METHODS: Nineteen 30-40 kg pigs were injected with 370 + 1110 MBq of Tc-99m sestamibi or tetrofosmin or 37 + 111 MBq of Tl-201 at rest + stress. Microspheres were injected simultaneously to measure MBF. The pigs were imaged in list-mode for 11 min starting at the time of injection using a Discovery NM 530c camera (GE Healthcare). Each list file was modified so that 3/4, 1/2, 1/4, 1/8, 1/16, and 1/32 of the original counts were included in the projections. Modified projections were reconstructed with CT-based attenuation correction and an energy window-based scatter correction and analyzed with FlowQuant kinetic modeling software using a 1-compartment model. A modified Renkin-Crone extraction function was used to convert the tracer uptake rate K1 to MBF values. The SPECT results were compared to those from microspheres. RESULTS: Correlation between SPECT and microsphere MBF values for the full injected activity was r ≥ 0.75 for all 3 tracers and did not significantly degrade over all count levels. The mean MBF and MFR and the standard errors in the estimates were not significantly worse than the full-count data at 1/4-counts (Tc99m-tracers) and 1/2-counts (Tl-201). CONCLUSIONS: Dynamic SPECT measurement of MBF and MFR in pigs can be performed with 1/4 (Tc99m-tracers) or 1/2 (Tl-201) of the standard injected activity without significantly reducing accuracy and precision.

Flow-Dependent Uptake of ¹²³I-CMICE-013, a Novel SPECT Perfusion Agent, Compared with Standard Tracers.

UNLABELLED: Rotenone derivatives have shown promise in myocardial perfusion imaging (MPI). CMICE-013 is a novel (123)I-labeled rotenone derivative developed for SPECT MPI. The objective of this study was to assess the image quality of CMICE-013 and compare its uptake with tetrofosmin, sestamibi, and (201)Tl in vivo in a porcine model of stress-induced myocardial ischemia. METHODS: Microspheres were injected simultaneously with the radiotracer injections at rest and stress to measure blood flow. Mimicking a 1-d tetrofosmin protocol, stress imaging used 3 times as much activity and occurred 1 h after the rest injection. SPECT images were obtained at both rest and stress. After imaging, the heart was sectioned into 44-50 pieces. In each heart sample, the tracer uptake was measured in a γ counter. The images were aligned, and the decay-corrected ratio of the signals at rest and stress was used to separate the well-counter signal into rest and stress components. The uptake at rest and stress was compared with microsphere flow measurements. RESULTS: The CMICE-013 images showed good contrast between the heart and surrounding organs, with heart-to-liver and heart-to-lung uptake ratios similar to those of the standard tracers. Uptake of CMICE-013 was 1.5% of the injected dose at rest and increased more rapidly with increased blood flow than did the standard SPECT tracers. The percentage injected dose of CMICE-013 taken up by the heart was greater (P < 0.05) than (201)Tl, tetrofosmin, or sestamibi at flows greater than 1.5 mL/min/g. CONCLUSION: CMICE-013 is a promising new SPECT MPI agent.

Dynamic SPECT measurement of absolute myocardial blood flow in a porcine model.

UNLABELLED: Absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) provide incremental diagnostic and prognostic information over relative perfusion alone. Recent development of dedicated cardiac SPECT cameras with better sensitivity and temporal resolution make dynamic SPECT imaging more practical. In this study, we evaluate the measurement of MBF using a multipinhole dedicated cardiac SPECT camera in a pig model of rest and transient occlusion at stress using 3 common tracers: (201)Tl, (99m)Tc-tetrofosmin, and (99m)Tc-sestamibi. METHODS: Animals (n = 19) were injected at rest/stress with (99m)Tc radiotracers (370/1,100 MBq) or (201)Tl (37/110 MBq) with a 1-h delay between rest and dipyridamole stress. With each tracer, microspheres were injected simultaneously as the gold standard measurement for MBF. Dynamic images were obtained for 11 min starting with each injection. Residual resting activity was subtracted from stress data and images reconstructed with CT-based attenuation correction and energy window-based scatter correction. Dynamic images were processed with kinetic analysis software using a 1-tissue-compartment model to obtain the uptake rate constant K(1) as a function of microsphere MBF. RESULTS: Measured extraction fractions agree with those obtained previously using ex vivo techniques. Converting K(1) back to MBF using the measured extraction fractions produced accurate values and good correlations with microsphere MBF: r = 0.75-0.90 (P < 0.01 for all). The correlation in the MFR was between r = 0.57 and 0.94 (P < 0.01). CONCLUSION: Noninvasive measurement of absolute MBF with stationary dedicated cardiac SPECT is feasible using common perfusion tracers.