Improvement of image quality using interpolated projection data estimation method in SPECT

Objective  

General data acquisition for single photon emission computed tomography (SPECT) is performed in 90 or 60 directions, with a coarse pitch of approximately 4–6° for a rotation of 360° or 180°, using a gamma camera. No data between adjacent projections will be sampled under these circumstances. The aim of the study was to develop a method to improve SPECT image quality by generating lacking projection data through interpolation of data obtained with a coarse pitch such as 6°.     

New reconstruction algorithm allows shortened acquisition time for myocardial perfusion SPECT

Purpose

Shortening scan time and/or reducing radiation dose at maintained image quality are the main issues of the current research in radionuclide myocardial perfusion imaging (MPI). We aimed to validate a new iterative reconstruction (IR) algorithm for SPECT MPI allowing shortened acquisition time (HALF time) while maintaining image quality vs. standard full time acquisition (FULL time).

Methods

In this study, 50 patients, referred for evaluation of known or suspected coronary artery disease by SPECT MPI using 99mTc-Tetrofosmin, underwent 1-day adenosine stress 300 MBq/rest 900 MBq protocol with standard (stress 15 min/rest 15 min FULL time) immediately followed by short emission scan (stress 9 min/rest 7 min HALF time) on a Ventri SPECT camera (GE Healthcare). FULL time scans were processed with IR, short scans were additionally processed with a recently developed software algorithm for HALF time emission scans. All reconstructions were subsequently analyzed using commercially available software (QPS/QGS, Cedars Medical Sinai) with/without X-ray based attenuation correction (AC). Uptake values (percent of maximum) were compared by regression and Bland-Altman (BA) analysis in a 20-segment model.

Results

HALF scans yielded a 96% readout and 100% clinical diagnosis concordance compared to FULL. Correlation for uptake in each segment (n?=?1,000) was r?=?0.87at stress (p?<?0.001) and r?=?0.89 at rest (p?<?0.001) with respective BA limits of agreement of ?11% to 10% and ?12% to 11%. After AC similar correlation (r?=?0.82, rest; r?=?0.80, stress, both p?<?0.001) and BA limits were found (?12% to 10%; ?13% to 12%).

Conclusion

With the new IR algorithm, SPECT MPI can be acquired at half of the scan time without compromising image quality, resulting in an excellent agreement with FULL time scans regarding to uptake and clinical conclusion.     

Rapid data acquisition protocol in ECG-gated myocardial perfusion SPECT with Tc-99m-tetrofosmin

Into 25 patients with heart disorders,^99mTc-tetrofosmin 555–740 MBq was injected intravenously at rest. After 40 minutes, ECG-gated myocardial perfusion SPECT was performed with a two detector gamma camera VERTEX (ADAC), setting up two detectors to form a 90-degree angle. Sixteen frames per R-R interval were acquired during a 180° rotation from the RAO 45° to the LPO 45°. A pair of data sets with standard (SDA) and rapid data acquisition (RDA) protocols was collected. In an SDA protocol, SPECT imaging was performed for 50 sec per step in 5° angular steps (total acquisition time; 15 minutes). An RDA protocol was conducted with 12 sec per step, 6° angular steps (acquisition time, 3 minutes). LVEF (%) and LVEDVml quantitated automatically with a QGS program showed excellent correlations between two protocols with correlation coefficients of 0.980 (p < 0.01) and 0.983 (p < 0.01), respectively. Subsequently visual assessment of regional wall motion based on a four-point grading system was carried out with a 3-D cine LV display. High complete agreement was gained with 158 (90.3%) out of total 175 segments, so that assessment of the global and regional LV function with the RDA protocol demonstrated high reliability and feasibility.     

A comparison of the image quality of full-time myocardial perfusion SPECT vs wide beam reconstruction half-time and half-dose SPECT

Objectives

Wide Beam Reconstruction (WBR) (UltraSPECT, Ltd) uses resolution recovery and noise modeling to cope with decreased SPECT count statistics. Because WBR processing reconstructs half the usual SPECT count statistics, we postulate that image quality equivalent to a full-time acquisition can be achieved in either half the time or with half the radiopharmaceutical activity.

Methods

In 156 consecutive patients (pts) rest and 8-frame gated post-stress myocardial perfusion SPECT was performed following 333-444 and 1184-1480 MBq (9-12 and 32-40 mCi) Tc-99m sestamibi injections, respectively, with full-time (rest = 14 min; stress = 12.3 min) acquisitions processed with OSEM and also separate “half-time” acquisitions processed with WBR. A subsequent group of 160 consecutive pts matched in gender, weight, and chest circumference received “half-dose” rest and stress injections 214.6 ± 22.2 and 647.5 ± 92.5 MBq (5.8 ± 0.6 and 17.5 ± 2.5 mCi) with full-time SPECT acquisitions. Image quality (1 = poor to 5 = excellent) was judged by myocardial count density and uniformity, endocardial edge definition, perfusion defect delineation, right ventricular visualization, and background noise.

Results

Mean image quality for rest, stress, and post-stress gated images were 3.6 ± 0.7, 3.8 ± 0.7, and 3.9 ± 1.0, respectively, for “full-time OSEM; 3.7 ± 0.8, 4.0 ± 0.7, and 4.8 ± 0.4 for “half-time” WBR; and 4.3 ± 0.8, 4.6 ± 0.6, and 4.7 ± 0.6 for “half-dose” WBR. “Half-time” and “half-dose” WBR image quality were both superior to standard full-time OSEM (P’s < .001). There was no significant difference between the summed stress and rest scores for “full-time” OSEM vs “half-time” WBR in 82 patients with perfusion defects.

Conclusions

Both “half-time” and “half-dose” WBR provide myocardial perfusion SPECT quality superior to full-time OSEM, with an associated decrease in scan acquisition time and patient radiation exposure, respectively.     

Value of exercise data for the interpretation of myocardial perfusion SPECT

BACKGROUND: Artificial neural networks have successfully been applied for automated interpretation of myocardial perfusion images. So far the networks have used data from the myocardial perfusion images only. The purpose of this study was to investigate whether the automated interpretation of myocardial perfusion images with the use of artificial neural networks was improved if clinical data were assessed in addition to the perfusion images. METHODS AND RESULTS: A population of 229 patients who had undergone both rest-stress myocardial perfusion scintigraphy in conjunction with an exercise test and coronary angiography, with no more than 3 months elapsing between the 2 examinations, were studied. The networks were trained to detect coronary artery disease or myocardial ischemia with the use of 2 different gold standards. The first was based on coronary angiography, and the second was based on all data available (including perfusion scintigrams, coronary angiography, exercise test, resting electrocardiography, patient history, etc). The performance of the neural networks was quantified as areas under the receiver operating characteristic curves. The results showed that the neural networks trained with perfusion images performed better than those trained with exercise data (0.78 vs 0.55, P <.0001), with coronary angiography used as the gold standard. Furthermore, the networks did not improve when data from the exercise test were used as input in addition to the perfusion images (0.78 vs 0.77, P =.6). CONCLUSIONS: The results show that the clinically important information in combined exercise test and myocardial scintigraphy could be found in the perfusion images. Exercise test information did not improve upon the accuracy of automated neural network interpretation of myocardial perfusion images in a receiver operator characteristic analysis of test accuracy.     

Feasibility of detecting cardiac torsion in myocardial perfusion gated SPECT data

BACKGROUND: The dynamic twisting component of cardiac motion is not accounted for by radionuclide techniques so that maps of perfusion and wall thickening are motion-blurred by torsion. This study examined whether torsion can be estimated from gated single photon emission computed tomography data and whether torsion corrections affect cardiac measurements. METHODS AND RESULTS: Technetium 99m sestamibi myocardial perfusion gated tomograms were selected retrospectively for 52 patients who had x-ray contrast arteriograms: 12 with normal perfusion (group 1), 12 with abnormal perfusion (group 2), and 28 studied after angioplasty (group 3). The 8 gated perfusion maps were transformed by contrast normalization, the count minimums of which were tracked to quantify torsion. Measured torsion was used to correct maps of perfusion and wall thickening. Torsion was found to be visually detectable equally well in groups 1 and 2. Apical torsion was significantly greater for group 1 than groups 2 and 3 (15 degrees +/- 9 degrees vs 9 degrees +/- 15 degrees and 2 degrees +/- 12 degrees ) and was opposite in sign for patients with apical aneurysms (-4 degrees +/- 13 degrees ) and for patients after coronary artery bypass grafting (CABG) (-4 degrees +/- 15 degrees ). Maximum percent count differences were 10% +/- 16% between torsion-corrected versus uncorrected perfusion maps. The greatest wall thickening differences were seen for patients with left ventricular apical aneurysms and for patients after CABG versus group 1 (10% +/- 6% and 8% +/- 6% vs 3% +/- 1%, respectively). CONCLUSIONS: It is feasible to detect cardiac torsion in the majority of Tc-99m sestamibi myocardial perfusion scans. Abnormal twisting patterns distinguished patients after CABG and those with left ventricular aneurysms from subjects with normal perfusion in a manner similar to magnetic resonance imaging observations.     

Early image acquisition using a solid-state cardiac camera for fast myocardial perfusion imaging

Background  

A novel ultra-fast solid-state cardiac camera (Discovery NM 530c, General Electric) allows much shorter acquisition times compared to standard dual-detector SPECT cameras. This design enables investigation of the potential for early myocardial perfusion imaging (MPI) following a rest injection of technetium-99m (Tc-99m) rather than the conventional 45-60 minute delay in image acquisition.     

双核素心肌SPECT的研究进展

目前,核素心肌SPECT仍是诊断冠心病及缺血性心脏病的准确、非创伤性检查手段。传统显像多采用201Tl、99Tcm-MIBI(99Tcm-甲氧基异丁基异腈)或18F-FDG(18F-氟代脱氧葡萄糖)静脉注射后行单核素SPECT心肌显像,为了解决单核素心肌显像的缺点,很多学者对双核素心肌SPECT的双核素药物、显像方法及临床应用进行了研究,并取得了满意的结果。     

Prognostic estimation of coronary artery disease risk with resting perfusion abnormalities and stress ischemia on myocardial perfusion SPECT

Background. The extent and severity of stress ischemia are strong predictors of coronary artery disease (CAD) events. Prognosis associated with myocardial perfusion single photon emission computed tomography (MPS) abnormalities on the resting scan as it relates to stress ischemia has been incompletely described. Methods and Results. The Myoview Prognosis Registry was a prospective consecutive series of 7849 outpatients enrolled from 5 geographically diverse centers. Patients were followed up for the occurrence of CAD events (nonfatal myocardial infarction [MI] or death related to MI, heart failure, or sudden cardiac death). Time to CAD event (n=545) was estimated by use of univariable and multivariable Cox proportional hazards models (risk adjusted by symptoms, risk factors, and comorbid conditions). For patients with no resting defects, overall CAD event rates were 1.2%, 8%, and 10% for patients with 0% ischemic myocardium, 1% to 4.9% ischemic myocardium, and 5% ischemic myocardium or greater, respectively (P<.0001). As the percent myocardium with resting defects worsened, overall CAD event rates increased, such that for patients with 10% or more of the rest myocardium with perfusion defects, cardiovascular death or MI rates ranged from 7% to 44% (P<.0001). In a model including both the percent of the myocardium with resting defects and the percent ischemia, both were highly predictive of CAD events (P<.0001). For every 1% increase in ischemic myocardium, there was a 7% increased risk of CAD events (P<.0001). A 3% increase in risk of CAD events was observed for patients with every 1% of the myocardium with resting defects (P<.0001). Conclusions. The estimation of CAD risk may be optimally estimated by use of a combination of resting MPS, reflecting a patient’s burden of disease, and MPS with provocative ischemia. Partial unrestricted grant support for this project was provided by GE Healthcare.     

Optimizing radiation dose and imaging time with conventional myocardial perfusion SPECT: Technical aspects

Journal of Nuclear Cardiology -     

The impact of acquisition protocol on the incidence of patient motion in 99mTc based myocardial perfusion SPECT

BACKGROUND: Myocardial perfusion single photon emission computed tomography (SPECT) artefacts introduced as a result of patient motion are known to produce artefacts that mimic the appearances of coronary artery disease. The advent of 99mTc based radiopharmaceuticals permits greater flexibility in patient scheduling, but variable physical demands of protocols may be associated with variations in the likelihood of patient motion. METHODS: A prospective cross-sectional study of 177 myocardial perfusion SPECT patients using 99mTc tetrofosmin was used to compare the incidence of visually detectable motion for three protocol variations. The rotating cinematic display and sinograms of the datasets were visually assessed by two experienced technologist observers blinded to the second observer's responses and the clinical outcome. RESULTS: Among the 354 individual studies analysed, 43.8% contained visually detectable motion. 36.2% of rest studies demonstrated visually detectable motion compared to 51.4% for stress (P<0.05). Fifty per cent of 1 day rest/stress studies demonstrated motion, 39.3% of 2 day rest/stress studies demonstrated motion, and 46.8% of 2 day stress/rest studies demonstrated motion. CONCLUSION: One day 99mTc based myocardial perfusion SPECT studies are 1.3 times more likely to contain motion than the 2 day rest/stress protocol. The 2 day stress/rest protocol is 1.2 times more likely to contain motion than the 2 day rest/stress. The stress study is 1.4 times more likely to contain motion than the rest study while the stress study performed first in the sequence is 1.4 times more likely to contain motion than the stress study performed second. The 2 day rest/stress protocol is the preferred protocol to minimize patient motion.     

Correct spatial normalization of myocardial perfusion SPECT improves detection of multivessel coronary artery disease

BACKGROUND: This study sought to improve the detection of multivessel coronary artery disease (CAD) with the use of rest and exercise single photon emission computed tomography (SPECT) perfusion scintigraphy by developing a processing scheme, which provides proper regional normalization of the images for interpretation. When SPECT perfusion images are interpreted, one area of myocardium serves as "normal." We hypothesized that if this "normal" region changes location from rest to stress, the stress images must be adjusted for proper interpretation. By taking into account the level of tracer activity in this "normal" area on the resting images, we could more accurately identify patients with multivessel CAD.Methods and results Dual-isotope rest (thallium 201) and exercise dobutamine or adenosine stress (technetium 99m sestamibi) perfusion SPECT studies were examined in 258 patients with 2- or 3-vessel CAD on coronary arteriography performed within 6 months of each other (mean interval, 19 days). If a shift in regional location of the "normal" segment from rest to stress was present, the images were (1) interpreted in the usual fashion for the number of vessels with ischemia (PRE-NORM) and (2) reinterpreted after quantitative normalization (ie, adjusting the display window until the intensity of the "normal" segment was matched at rest and stress [POST-NORM]). Interpretation was performed with blinding to arteriographic results. An angiographic stenosis was defined as luminal diameter stenosis greater than 50%. Three control groups comprising (1) single-vessel CAD (n = 119), (2) no significant angiographic CAD (n = 118), and (3) a normalcy group of low pre- and post-test probability of CAD (n = 44) were also studied to determine the incidence of false-positive results induced by the renormalization technique. A shift in the "normal" segment occurred in 81 studies of 258 patients (31%), 80 of which were read as abnormal PRE-NORM (sensitivity, 99%); however, for their 216 stenosed vessels, only 143 were detected PRE-NORM (vessel sensitivity, 66%; accuracy, 65%). The mean POST-NORM change in the display was 11%. POST-NORM, all 82 patients' studies were interpreted as abnormal (sensitivity, 100%), and 196 of 216 vascular territories were abnormal (vessel sensitivity, 91%; accuracy, 83%; both P <.0001 vs PRE-NORM). In the single-vessel disease, no significant disease, and normalcy groups, 19 of 119, 15 of 118, and 11 of 44 patients, respectively, demonstrated a shift in the peak pixel location. However, there were no significant changes in single-vessel sensitivity, angiographic specificity, or normalcy in these patients. CONCLUSIONS: With multivessel CAD, the "normal" region on SPECT often changes in location from rest to stress, potentially masking the extent and severity of multivessel ischemia. Renormalization of the images to match their resting level before image interpretation allows diagnosis of contralateral ischemia and strikingly improves the detection of multivessel CAD, without a substantive loss in specificity.     

Motion-frozen myocardial perfusion SPECT improves detection of coronary artery disease in obese patients.

In this study, we compared the diagnostic performance of the standard SPECT with motion-frozen (MF) myocardial perfusion SPECT (MPS) in obese patients. METHODS: A total of 90 consecutive obese patients (body mass index, 30.1-46.8, average, 34.3 +/- 3.6; age, 63 +/- 12 y; 30% women) underwent standard supine rest (201)Tl/stress (99m)Tc dual-isotope gated MPS and cardiac catheterization within 3 mo. MF images were obtained by nonlinear warping of cardiac phases to the end-diastolic position. Total perfusion deficit (TPD) was obtained for summed (S-TPD) and motion-frozen (MF-TPD) datasets with sex-specific standard and MF normal limits. RESULTS: The area under the receiver-operating-characteristic (ROC) curve for detection of coronary artery disease (CAD) by MF-TPD was significantly larger than that for S-TPD (0.93 +/- 0.25 vs. 0.88 +/- 0.32, P < 0.05). MF-TPD had higher specificity (77% vs. 55%, P < 0.05) and accuracy (89% vs. 80%, P < 0.05) than did S-TPD. CONCLUSION: MF processing of MPS improves CAD detection in obese patients.     

Shortening MR image acquisition time for volumetric interpolated breath-hold examination with a recently developed parallel imaging reconstruction technique: clinical feasibility

A recently developed parallel magnetic resonance (MR) imaging technique, parallel imaging with an augmented radius in k space, was used to accelerate the volumetric interpolated breath-hold examination (VIBE) performed in 20 patients referred for clinical liver imaging. Nonaccelerated MR images were also acquired in these patients. A five-point scale was used to score the quality of the images. The acceleration resulted in reduced image quality: The nonaccelerated images had a significantly higher (P <.05) mean score--3.8 +/- 0.3 (SD), indicating good quality--than the accelerated images--3.0 +/- 0.3, indicating acceptable quality. However, for three patients who could not hold their breath for the duration necessary for nonaccelerated imaging, less severe breathing artifacts on the accelerated images resulted in improved quality compared with the quality of the nonaccelerated images. Parallel MR imaging-accelerated VIBE may be beneficial for patients who have difficulty sustaining a breath hold for the duration necessary to perform nonaccelerated imaging.     

门控断层显像在心肌灌注断层显像中的应用

使用门控心肌断层显像不但减低了心脏搏动产生的图像边缘模糊,提高了对心肌缺血诊断的灵敏度和特异性,而且通过傅立叶变换和图像边缘识别技术等图像处理技术,可以在一次采集的信息基础上同时获得心脏的心肌血流灌注、心肌活力、室壁运动、射血功能和收缩协调性等参数,提高了核素心脏检查的价值,为临床准确判断患者的心脏状况,选择治疗方案,预后及疗效评价提供了更可靠的数据。本文就其近年来的临床应用进行综述。     

MRS algorithm: a new method for searching myocardial region in SPECT myocardial perfusion images.

First, the necessity of automatically segmenting myocardium from myocardial SPECT image is discussed in Section 1. To eliminate the influence of the background, the optimal threshold segmentation method modified for the MRS algorithm is explained in Section 2. Then, the image erosion structure is applied to identify the myocardium region and the liver region. The contour tracing method is introduced to extract the myocardial contour. To locate the centriod of the myocardium, the myocardial centriod searching method is developed. The protocol of the MRS algorithm is summarized in Section 6. The performance of the MRS algorithm is investigated and the conclusion is drawn in Section 7. Finally, the importance of the MRS algorithm and the improvement of the MRS algorithm are discussed.