Takahiro Konishi

Creation and characterization of normal myocardial perfusion imaging databases using the IQ·SPECT system

BackgroundImage acquisition by short-time single-photon emission-computed tomography (SPECT) has been made feasible by IQ·SPECT. The aim of this study was to generate normal databases (NDBs) of thallium-201 (201Tl) myocardial perfusion imaging for IQ·SPECT, and characterize myocardial perfusion distribution.Methods and resultsWe retrospectively enrolled 159 patients with a low likelihood of cardiac diseases from four hospitals in Japan. All patients underwent short-time 201Tl myocardial perfusion IQ·SPECT with or without attenuation and scatter correction (ACSC) in either supine or prone position. The mean myocardial counts were calculated using 17-segment polar maps. Three NDBs were derived from supine and prone images as well as supine images with ACSC. Differences between the supine and prone positions were observed in the uncorrected sex-segregated NDBs in the mid-inferolateral counts (p ≤ 0.016 for males and p ≤ 0.002 for females). Differences between IQ·SPECT and conventional SPECT were also observed in the mid-anterior, inferolateral, and apical lateral counts (p ≤ 0.009 for males and p ≤ 0.003 for females). Apical low counts attributed to myocardial thinning were observed in the apical anterior and apex segments in the supine IQ·SPECT NDB with ACSC.ConclusionsThere were significant differences between uncorrected supine and prone NDBs, between uncorrected supine NDB and supine NDB with ACSC, and between uncorrected supine NDB and conventional SPECT NDB. Understanding the pattern of normal distribution in IQ-SPECT short-time acquisitions with and without ACSC will be helpful for interpretation of imaging findings in patients with coronary artery disease (CAD) or low likelihood of CAD and the NDBs will aid in quantitative analysis.

Validation of Left Ventricular Ejection Fraction with the IQ•SPECT System in Small-Heart Patients

The IQ•SPECT system, which is equipped with multifocal collimators (SMARTZOOM) and uses ordered-subset conjugate gradient minimization as the reconstruction algorithm, reduces the acquisition time of myocardial perfusion imaging compared with conventional SPECT systems equipped with low-energy high-resolution collimators. We compared the IQ•SPECT system with a conventional SPECT system for estimating left ventricular ejection fraction (LVEF) in patients with a small heart (end-systolic volume < 20 mL). Methods: The study consisted of 98 consecutive patients who underwent a 1-d stress–rest myocardial perfusion imaging study with a 99mTc-labeled agent for preoperative risk assessment. Data were reconstructed using filtered backprojection for conventional SPECT and ordered-subset conjugate gradient minimization for IQ•SPECT. End-systolic volume, end-diastolic volume, and LVEF were calculated using quantitative gated SPECT (QGS) and cardioREPO software. We compared the LVEF from gated myocardial perfusion SPECT to that from echocardiographic measurements. Results: End-diastolic volume, end-systolic volume, and LVEF as obtained from conventional SPECT, IQ•SPECT, and echocardiography showed a good to excellent correlation regardless of whether they were calculated using QGS or using cardioREPO. Although LVEF calculated using QGS significantly differed between conventional SPECT and IQ•SPECT (65.4% ± 13.8% vs. 68.4% ± 15.2%) (P = 0.0002), LVEF calculated using cardioREPO did not (69.5% ± 10.6% vs. 69.5% ± 11.0%). Likewise, although LVEF calculated using QGS significantly differed between conventional SPECT and IQ•SPECT (75.0 ± 9.6 vs. 79.5 ± 8.3) (P = 0.0005), LVEF calculated using cardioREPO did not (72.3% ± 9.0% vs. 74.3% ± 8.3%). Conclusion: In small-heart patients, the difference in LVEF between IQ•SPECT and conventional SPECT was less when calculated using cardioREPO than when calculated using QGS.

Technical Aspects: Image Reconstruction

Recent developments in nuclear medicine technology have been remarkable, with new technologies emerging in both hardware and software. In this study, we focused on an image reconstruction method known as the ordered subset conjugate gradient minimizer (OSCGM) method. We conducted a myocardial phantom experiment and a clinical study to examine the difference between this technology and conventional methods as well as the characteristics of an IQ-SPECT system with this technology. The outline is shown.

Elimination of scattered gamma rays from injection sites using upper offset energy windows in sentinel lymph node scintigraphy.

ObjectiveThe identification of sentinel lymph nodes (SLNs) near injection sites is difficult because of scattered gamma rays. The purpose of this study was to investigate the optimal energy windows for elimination of scattered gamma rays in order to improve the detection of SLNs. MethodsThe clinical study group consisted of 56 female patients with breast cancer. While the energy was centred at 140 keV with a 20% window for Tc-99m, this energy window was divided into five subwindows with every 4% in planar imaging. Regions of interest were placed on SLNs and the background, and contrast was calculated using a standard equation. The confidence levels of interpretations were evaluated using a five-grade scale. ResultsThe contrast provided by 145.6 keV±2% was the best, followed by 140 keV±2%, 151.2 keV±2%, 134.4 keV±2% and 128.8 keV±2% in that order. When 128.8 keV±2% and 134.4 keV±2% were eliminated from 140 keV±10% (145.6 keV±6%), the contrast of SLNs improved significantly. The confidence levels of interpretation and detection rate provided by the planar images with 140 keV±10% were 4.74±0.58 and 94.8%, respectively, and those provided by 145.6 keV±6% were 4.94±0.20 and 100%. ConclusionBecause lower energy windows contain many scattered gamma rays, upper offset energy windows, which exclude lower energy windows, improve the image contrast of SLNs near injection sites.

The Optimal Reconstruction Parameters by Scatter and Attenuation Corrections Using Multi-focus Collimator System in Thallium-201 Myocardial Perfusion SPECT Study

The aim of this study was to reveal the optimal reconstruction parameters of ordered subset conjugates gradient minimizer (OSCGM) by no correction (NC), attenuation correction (AC), and AC+scatter correction (ACSC) using IQ-single photon emission computed tomography (SPECT) system in thallium-201 myocardial perfusion SPECT. Myocardial phantom acquired two patterns, with or without defect. Myocardial images were performed 5-point scale visual score and quantitative evaluations using contrast, uptake, and uniformity about the subset and update (subset×iteration) of OSCGM and the full width at half maximum (FWHM) of Gaussian filter by three corrections. We decided on optimal reconstruction parameters of OSCGM by three corrections. The number of subsets to create suitable images were 3 or 5 for NC and AC, 2 or 3 for ACSC. The updates to create suitable images were 30 or 40 for NC, 40 or 60 for AC, and 30 for ACSC. Furthermore, the FWHM of Gaussian filters were 9.6 mm or 12 mm for NC and ACSC, 7.2 mm or 9.6 mm for AC. In conclusion, the following optimal reconstruction parameters of OSCGM were decided; NC: subset 5, iteration 8 and FWHM 9.6 mm, AC: subset 5, iteration 8 and FWHM 7.2 mm, ACSC: subset 3, iteration 10 and FWHM 9.6 mm.

Prototype imaging protocols for monitoring the efficacy of iodine-131 ablation in differentiated thyroid cancer.

Whole-body and single photon emission tomography (SPET) images during sodium iodide-131 (Na131I) ablation are useful to confirm the efficacy of ablation using 131I imaging. However, there have been no attempts to improve the quality of 131I imaging. We therefore investigated imaging protocols for 131I imaging in differentiated thyroid cancer (DTC). Phantoms containing 131I were used to simulate extra-thyroid beds and thyroid beds. To simulate extra-thyroid beds, a phantom containing 0.19, 0.37, 0.74 or 1.85 MBq was placed in the acquisition center. To simulate the thyroid beds, four phantoms were applied as normal thyroid tissue, and four phantoms containing 0.19, 0.37, 0.74 and 1.85 MBq were arranged around normal thyroid tissue as a cancer. Whole-body imaging was performed at different table speeds, and SPET data acquired with various pixel sizes were reconstructed using a filtered backed projection (FBP) and ordered-subsets expectation maximization with 3-dimensional (OSEM-3D) algorithm. We measured full width at half maximum (FWHM) and % coefficient of variation (%CV). Patients were then examined based on the results of phantom studies. In extrathyroid beds, slower table speed in whole-body imaging improved %CV, but had little effect on FWHM. For SPET imaging OSEM-3D produced high-resolution and low-noise images, and FWHM and %CV improved with smaller pixel size, as compared with FBP. In the thyroid beds, only the 1.85 MBq phantom could be confirmed on whole-body imaging. Images by SPET had high FWHM and low %CV when the smaller pixel size and OSEM-3D were applied. Accumulation of ≤1.85 MBq was detected with a smaller pixel size of ≤4.8 mm and OSEM-3D. For Na131I ablation imaging, slower scan speed is suitable for whole-body imaging and smaller pixel size and OSEM-3D is appropriate for SPET imaging. In conclusion, we confirmed Na131I accumulation in thyroid beds using slower scan speed (≤15 cm/min) on whole-body imaging, and then accurate identification of Na131I accumulation using SPET and CT fusion imaging with smaller pixel size (≤4.8 mm) and OSEM-3D.

Characteristics of iodine-123 IQ-SPECT/CT imaging compared with conventional SPECT/CT

ObjectivesAlthough the utility of IQ-SPECT imaging using 99mTc and 201Tl myocardial perfusion SPECT has been reported, 123I-labeled myocardial SPECT has not been fully evaluated. We determined the characteristics and utility of 123I IQ-SPECT imaging compared with conventional SPECT (C-SPECT).MethodsTwo myocardial phantom patterns were used to simulate normal myocardium and myocardial infarction. SPECT acquisition was performed using a hybrid dual-head SPECT/CT system equipped with a SMARTZOOM collimator for IQ-SPECT or a low-medium energy general purpose collimator for C-SPECT. Projection data were reconstructed using ordered subset expectation maximization with depth-dependent 3-dimensional resolution recovery for C-SPECT and ordered subset conjugate gradient minimizer method for IQ-SPECT. Three types of myocardial image were created; namely, no correction (NC), with attenuation correction (AC), and with both attenuation and scatter corrections (ACSC). Five observers visually scored the homogeneity of normal myocardium and defect severity of the myocardium with inferior defects by a five-point scale: homogeneity scores (5 = homogeneous to 1 = inhomogeneous) and defect scores (5 = excellent to 1 = poor). We also created a 17-segment polar map and quantitatively assessed segmental %uptake using a myocardial phantom with normal findings and defects.ResultsThe average visual homogeneity scores of the IQ-SPECT with NC and ACSC were significantly higher than that of C-SPECT, whereas the average visual defect scores of IQ-SPECT with AC and ACSC were significantly lower. The %uptake of all segments for IQ-SPECT with NC was significantly higher than that of C-SPECT. Furthermore, the subtraction of %uptake for C-SPECT and IQ-SPECT was the largest in inferior wall, which was approximately 10.1%, 14.7% and 14.4% for NC, AC and ACSC, respectively. The median % uptake values of the inferior wall with defect areas for C-SPECT and IQ-SPECT were 46.9% and 50.7% with NC, 59.8% and 69.2% with AC, and 54.7% and 66.5% with ACSC, respectively.Conclusion123I IQ-SPECT imaging significantly improved the attenuation artifact compared with C-SPECT imaging. Although the defect detectability of IQ-SPECT was inferior to that of C-SPECT, 123I IQ-SPECT images with NC and ACSC met the criteria for defect detectability. Use of 123I IQ-SPECT is suitable for routine examinations.