Multicenter investigation comparing a highly efficient half-time stress-only attenuation correction approach against standard rest-stress Tc-99m SPECT imaging

Accurate and efficient rapid acquisition early post-injection stress-first CZT SPECT myocardial perfusion imaging with tetrofosmin and attenuation correction

INTRODUCTION

Myocardial perfusion imaging (MPI) protocols have not changed significantly despite advances in instrumentation and software. We compared an early post-injection, stress-first SPECT protocol to standard delayed imaging.

METHODS

95 patients referred for SPECT MPI were imaged upright and supine on a Spectrum Dynamics D-SPECT CZT system with CT attenuation correction. Patients received injection of 99mTc tetrofosmin at peak of regadenoson stress and were imaged. Early post-stress (mean 17 ± 2 minutes) and Standard 1-h delay (mean 61 ± 13 min). Three blinded readers evaluated images for overall interpretation, perceived need for rest imaging, image quality, and reader confidence. Laboratory efficiency was also evaluated.

RESULTS

Blinded readers had the same response for the need for rest in 77.9% of studies. Studies also had the same interpretation in 89.5% of studies. Reader confidence was high (86.0% (Early) and 90.3% (Standard p = 0.52. Image quality was good or excellent in 87.4% Early vs 96.8% Standard (p = 0.09). Time between patient check-in and end of stress imaging was 104 ± (Standard) to 60 ± 18 minutes (Early) (p < 0.001).

CONCLUSION

Early post-injection stress-only imaging using CZT SPECT/CT appears promising with Tc-99m tetrofosmin with similar image quality, reader confidence, diagnosis, and need for a rest scan.

Can the Diagnostic Accuracy of Bone Scintigraphy be Maintained with Half the Scanning Time?

Purpose: We aim to show that the acquisition time of a conventional bone scan can be reduced by one-half without loss of the diagnostic value of the scan. Materials and Methods: Fifty adult patients (37 male and 13 female, mean age 62.5, SD 8.7 years) were enrolled. Patients were injected with 25-30 mCi (925-1110 MBq) ^99mTc MDP IV. The Standard Protocol whole body planar images were acquired first [scan speed = 10 cm/min, acquisition time around 20 minutes] and were followed immediately by the Half-Time Protocol whole body planar images [scan speed = 20 cm/min; acquisition time around 10 minutes]. Both images were interpreted by two nuclear medicine physicians. Each reviewer, when reviewing the Standard Protocol images, was "self-blinded" to the result they had obtained when reviewing the Half-Time images, and vice-versa. This self-blinding was accomplished by allowing a minimum of two weeks to elapse between the two interpretations. We used the κ-coefficient to compare the agreement between the Standard-Protocol results and the Half-Time results. Results: There was no difference in clinically significant diagnostic information for Half -Time and Standard Protocol. The diagnostic quality of Half-Time and the Standard Protocol images were not significantly different (0.86 < κ < 1.0). Conclusion: Our data suggest that if we reduce the ^99mTc MDP dose by half and keep the acquisition time at its standard value we gain the benefits of reduced dose without loss of diagnostic value of the scan.

Retrospective fractional dose reduction in Tc-99m cardiac perfusion SPECT/CT patients: A human and model observer study

BACKGROUND

In the ongoing efforts to reduce cardiac perfusion dose (injected radioactivity) for conventional SPECT/CT systems, we performed a human observer study to confirm our clinical model observer findings that iterative reconstruction employing OSEM (ordered-subset expectation-maximization) at 25% of the full dose (quarter-dose) has a similar performance for detection of hybrid cardiac perfusion defects as FBP at full dose.

METHODS

One hundred and sixty-six patients, who underwent routine rest-stress Tc-99m sestamibi cardiac perfusion SPECT/CT imaging and clinically read as normally perfused, were included in the study. Ground truth was established by the normal read and the insertion of hybrid defects. In addition to the reconstruction of the 25% of full-dose data using OSEM with attenuation (AC), scatter (SC), and spatial resolution correction (RC), FBP and OSEM (with AC, SC, and RC) both at full dose (100%) were done. Both human observer and clinical model observer confidence scores were obtained to generate receiver operating characteristics (ROC) curves in a task-based image quality assessment.

RESULTS

Average human observer AUC (area under the ROC curve) values of 0.725, 0.876, and 0.890 were obtained for FBP at full dose, OSEM at 25% of full dose, and OSEM at full dose, respectively. Both OSEM strategies were significantly better than FBP with P values of 0.003 and 0.01 respectively, while no significant difference was recorded between OSEM methods (P = 0.48). The clinical model observer results were 0.791, 0.822, and 0.879, respectively, for the same patient cases and processing strategies used in the human observer study.

CONCLUSIONS

Cardiac perfusion SPECT/CT using OSEM reconstruction at 25% of full dose has AUCs larger than FBP and closer to those of full-dose OSEM when read by human observers, potentially replacing the higher dose studies during clinical reading.

Drivers of radiation dose reduction with myocardial perfusion imaging: A large health system experience

BACKGROUND

Despite increasing emphasis on reducing radiation exposure from myocardial perfusion imaging (MPI), the use of radiation-sparing practices (RSP) at nuclear laboratories remains limited. Defining real-world impact of RSPs on effective radiation dose (E) can potentially further motivate their adoption.

METHODS

MPI studies performed between 1/2010 and 12/2016 within a single health system were included. Mean E was compared between sites with 'basic' RSP (defined as elimination of thallium-based protocols and use of stress-only (SO) imaging on conventional single photon emission computed tomography (SPECT) cameras) and those with 'advanced' capabilities (sites that additionally used solid-state detector (SSD) SPECT cameras, advanced post-processing software (APPS) or positron emission tomography (PET) imaging), after matching patients by age, gender, and weight. Contributions of individual RSP to E reduction were determined using multiple linear regression after adjusting for factors affecting tracer dose.

RESULTS

Among 55,930 MPI studies performed, the use of advanced RSP was associated with significantly lower mean E compared to basic RSP (7 ± 5.6 mSv and 16 ± 5.4 mSv, respectively; P < 0.001), with a greater likelihood of achieving E < 9 mSv (65.7% vs. 10.8%, respectively; OR 15.8 [95% CI 14 to 17.8]; P < 0.0001). Main driver of E reduction was SO-SSD SPECT (mean reduction = 11.5 mSv), followed by use of SO-SPECT + APPS (mean reduction = 10.1 mSv), ;ET (mean reduction = 9.7 mSv); and elimination of thallium protocols (mean reduction = 9.1 mSv); P < 0.0001 for all comparisons.

CONCLUSION

In a natural experiment with implementation of radiation-saving practices at a large health system, stress-only protocols used in conjunction with modern SPECT technologies, the use of PET and elimination of thallium-based protocols were associated with greatest reductions in radiation dose. Availability of several approaches to dose reduction within a health system can facilitate achievement of targeted radiation benchmarks in a greater number of performed studies.

Impact of iterative reconstruction with resolution recovery in myocardial perfusion SPECT: phantom and clinical studies

The corrections of photon attenuation, scatter, and depth-dependent blurring improve image quality in myocardial perfusion single-photon emission computed tomography (SPECT) imaging; however, the combined corrections induce artifacts. Here, we present the single correction method of depth-dependent blurring and its impact for myocardial perfusion distribution in phantom and clinical studies. The phantom and clinical patient images were acquired with two conditions: circular and noncircular orbits of gamma cameras yielded constant and variable depth-dependent blurring, respectively. An iterative reconstruction with the correction method of depth-dependent was used to reconstruct the phantom and clinical patient images. We found that the single correction method improved the robustness of phantom images whether the images contained constant or variable depth-dependent blurring. The myocardial perfusion databases generated from 72 normal patients exhibited uniform perfusion distribution of whole myocardium. In summary, the single correction method of depth-dependent blurring with iterative reconstruction is helpful for myocardial perfusion SPECT.

Personalized Models for Injected Activity Levels in SPECT Myocardial Perfusion Imaging

We propose a patient-specific ("personalized") approach for tailoring the injected activities to individual patients in order to achieve dose reduction in SPECT-myocardial perfusion imaging (MPI). First, we develop a strategy to determine the minimum dose levels required for each patient in a large set of clinical acquisitions (857 subjects) such that the reconstructed images are sufficiently similar to that obtained at conventional clinical dose. We then apply machine learning models to predict the required dose levels on an individual basis based on a set of patient attributes which include body measurements and various clinical variables. We demonstrate the personalized dose models for two commonly used reconstruction methods in clinical SPECT-MPI: 1) conventional filtered backprojection (FBP) with post-filtering and 2) ordered-subsets expectation-maximization (OS-EM) with corrections for attenuation, scatter and resolution, and evaluate their performance in perfusion-defect detection by using the clinical Quantitative Perfusion SPECT software package. The results indicate that the achieved dose reduction can vary greatly among individuals from their conventional clinical dose and that the personalized dose models can achieve further reduction on average compared with a global (non-patient specific) dose reduction approach. In particular, the average personalized dose level can be reduced to 58% and 54% of the full clinical dose, respectively, for FBP and OS-EM reconstruction, while without deteriorating the accuracy in perfusion-defect detection. Furthermore, with the average personalized dose further reduced to only 16% of full dose, OS-EM can still achieve a detection accuracy level comparable to that of FBP with full dose.

Investigation of dose reduction in cardiac perfusion SPECT via optimization and choice of the image reconstruction strategy

BACKGROUND

We investigated the extent to which the administered dose (activity) level can be reduced without sacrificing diagnostic accuracy for three reconstruction strategies for SPECT-myocardial perfusion imaging (MPI).

METHODS

We optimized the parameters of the three reconstruction strategies for perfusion-defect detection over a range of simulated administered dose levels using a set of hybrid studies (derived from 190 subjects) consisting of clinical SPECT-MPI data modified to contain realistic simulated lesions. The optimized strategies we considered are filtered backprojection (FBP) with no correction for degradations, ordered-subsets expectation-maximization (OS-EM) with attenuation correction (AC), scatter correction (SC), and resolution correction (RC), and OS-EM with scatter and resolution correction only. Each study was evaluated using a total perfusion deficit (TPD) score computed by the Quantitative Perfusion SPECT (QPS) software package. We conducted a receiver operating characteristics (ROC) study based on the TPD scores for each dose level and reconstruction strategy.

RESULTS

For FBP, the achieved optimum values of the area under the ROC curve (AUC) at 100%, 50%, 25%, and 12.5% of standard dose were 0.75, 0.74, 0.72, and 0.70, respectively, compared to 0.81, 0.79, 0.76, and 0.74 for OS-EM with AC-SC-RC and 0.78, 0.77, 0.74, 0.72 for OS-EM with SC-RC.

CONCLUSIONS

Our results suggest that studies reconstructed by OS-EM with AC-SC-RC could possibly be reduced, on average, to 25% of the originally administered dose without causing diagnostic accuracy (AUC) to decrease below that of FBP.

Contemporary Cardiac SPECT Imaging-Innovations and Best Practices: An Information Statement from the American Society of Nuclear Cardiology

This information statement from the American Society of Nuclear Cardiology highlights advances in cardiac SPECT imaging and supports the incorporation of new technology and techniques in laboratories performing nuclear cardiology procedures. The document focuses on the application of the latest imaging protocols and the utilization of newer hardware and software options to perform high quality, state-of-the-art SPECT nuclear cardiology procedures. Recommendations for best practices of cardiac SPECT imaging are discussed, highlighting what imaging laboratories should be doing as the standard of care in 2018 to achieve optimal results (based on the ASNC 2018 SPECT guideline [Dorbala et al., J Nucl Cardiol. 2018. https://doi.org/10.1007/s12350-018-1283-y ]).

Downstream indication to revascularization following hybrid cardiac PET/MRI: preliminary results

BACKGROUND

Hybrid PET/MRI allows the acquisition of both fluorine-18-fluorodeoxyglucose (F-FDG) PET and cardiac magnetic resonance (CMR) during one session. Whether this will result in different referral to coronary revascularization (CR) is unknown. We compared this new hybrid method with all-nuclear/all-CMR methods in the assessment of viable myocardium and in downstream referral to CR.

PATIENTS AND METHODS

Overall, 12 patients with rest perfusion defects on a single photon emission computed tomography (SPECT) were recruited for cardiac viability assessment using a PET/MRI device. Perfusion (SPECT and CMR), metabolism, late gadolinium enhancement (LGE), and contractility were compared using a 20-segments bull's eye for agreement. The patterns of ischemia/viability were compared between all-nuclear, all-CMR, and hybrid methods. Downstream CR was proposed after correlating findings to coronary angiography.

RESULTS

The SPECT and CMR perfusion denoted poor agreement [agreement rate (AR): 60%; κ: 0.191, P<0.004]. The added PET metabolism concurred in reclassifying 19.2% of segments with intermediate or unassessable LGE using the hybrid method. Overall, the all-CMR method showed better agreement with the hybrid method than the all-nuclear method for findings of normal (AR: 100%, κ: 1.00 vs. 65.8% %; κ: 0.347, respectively; P<0.001), scar (AR: 85%; κ: 0.675 vs. 80.8%; κ: 0.596, respectively; P<0.001), and ischemic segments (AR: 95.8%; κ: 0.881 vs. 75.8%; κ: 0.168, respectively; P<0.001). Downstream CR was proposed in four, 11, and 12 vessels by the all-nuclear, all-CMR, or hybrid methods, respectively.

CONCLUSION

Compared with all-CMR, the hybrid method allowed the reclassification of 19.2% segments. Using CMR perfusion instead of SPECT perfusion had a significant impact on downstream target vessel revascularization.

Reducing radiation to patients and improving image quality in a real-world nuclear cardiology laboratory

In part because of aging equipment and reduced reimbursement for imaging services in the last several years, nuclear cardiologists who remain in private practice face challenges in maintaining high quality and in reducing radiation exposure to patients. We review patient-centered approaches and affordable software solutions employed in our practice combined with supine-prone myocardial perfusion imaging to achieve increased interpretive confidence with reduced radiation exposure to patients.

Stress-only myocardial perfusion scintigraphy: a prospective study on the accuracy and observer agreement with quantitative coronary angiography as the gold standard

OBJECTIVE

Patients with normal stress perfusion have an excellent prognosis. Prospective studies on the diagnostic accuracy of stress-only scans with contemporary, independent examinations as gold standards are lacking.

PATIENTS AND METHODS

A total of 109 patients with typical angina and no previous coronary artery disease underwent a 2-day stress (exercise)/rest, gated, and attenuation-corrected (AC), 99m-technetium-sestamibi perfusion study, followed by invasive coronary angiography. The stress datasets were evaluated twice by four physicians with two different training levels (expert and novice): familiar and unfamiliar with AC. The two experts also made a consensus reading of the integrated stress-rest datasets. The consensus reading and quantitative data from the invasive coronary angiography were applied as reference methods.

RESULTS

The sensitivity/specificity were 0.92-1.00/0.73-0.90 (reference: expert consensus reading), 0.93-0.96/0.63-0.82 (reference: ≥1 stenosis>70%), and 0.75-0.88/0.70-0.88 (reference: ≥1 stenosis>50%). The four readers showed a high and fairly equal sensitivity independent of their familiarity with AC. The expert familiar with AC had the highest specificity independent of the reference method. The intraobserver and interobserver agreements on the stress-only readings were good (readers without AC experience) to excellent (readers with AC experience).

CONCLUSION

AC stress-only images yielded a high sensitivity independent of the training level and experience with AC of the nuclear physician, whereas the specificity correlated positively with both. Interobserver and intraobserver agreements tended to be the best for physicians with AC experience.

Novel SPECT Technologies and Approaches in Cardiac Imaging

Recent novel approaches in myocardial perfusion single photon emission CT (SPECT) have been facilitated by new dedicated high-efficiency hardware with solid-state detectors and optimized collimators. New protocols include very low-dose (1 mSv) stress-only, two-position imaging to mitigate attenuation artifacts, and simultaneous dual-isotope imaging. Attenuation correction can be performed by specialized low-dose systems or by previously obtained CT coronary calcium scans. Hybrid protocols using CT angiography have been proposed. Image quality improvements have been demonstrated by novel reconstructions and motion correction. Fast SPECT acquisition facilitates dynamic flow and early function measurements. Image processing algorithms have become automated with virtually unsupervised extraction of quantitative imaging variables. This automation facilitates integration with clinical variables derived by machine learning to predict patient outcome or diagnosis. In this review, we describe new imaging protocols made possible by the new hardware developments. We also discuss several novel software approaches for the quantification and interpretation of myocardial perfusion SPECT scans.

Myocardial perfusion scintigraphy dosimetry: optimal use of SPECT and SPECT/CT technologies in stress-first imaging protocol

Purpose

Over the past decade, nuclear medicine experts have been seeking to minimize patient exposure to radiation in myocardial perfusion scintigraphy (MPS). This review describes the latest technological innovations in MPS, particularly with regard to dose reduction.

Methods

We searched in PubMed for original clinical papers in English, published after 2008, using the following research criteria: (dose) and ((reduction) or (reducing)) and ((myocardial) or (cardiac) or (heart)) and ((nuclear medicine) or (nuclear imaging) or (radionuclide) or (scintigraphy) or (SPET) or (SPECT)). Thereafter, recent reviews on the topic were considered and other relevant clinical papers were added to the results.

Results

Of 202 non-duplicate articles, 17 were included. To these, another eight papers cited in recent reviews were added. By optimizing the features of software, i.e., through algorithms for iterative reconstruction with resolution recovery (IRRs), and hardware, i.e., scanners and collimators, and by preferring, unless otherwise indicated, the use of stress-first imaging protocols, it has become possible to reduce the effective dose by at least 50% in stress/rest protocols, and by up to 89% in patients undergoing a diagnostic stress-only study with new technology. With today’s SPECT/CT systems, the use of a stress-first protocol can conveniently be performed, resulting in an overall dose reduction of about 35% if two-thirds of stress-first examinations were considered definitively normal.

Conclusion

Using innovative gamma cameras, collimators and software, as well as, unless otherwise indicated, stress-first imaging protocols, it has become possible to reduce significantly the effective dose in a high percentage of patients, even when X-ray CT scanning is performed for attenuation correction.

Normal Databases for the Relative Quantification of Myocardial Perfusion

PURPOSE OF REVIEW

Myocardial perfusion imaging (MPI) with SPECT is performed clinically worldwide to detect and monitor coronary artery disease (CAD). MPI allows an objective quantification of myocardial perfusion at stress and rest. This established technique relies on normal databases to compare patient scans against reference normal limits. In this review, we aim to introduce the process of MPI quantification with normal databases and describe the associated perfusion quantitative measures that are used.

RECENT FINDINGS

New equipment and new software reconstruction algorithms have been introduced which require the development of new normal limits. The appearance and regional count variations of normal MPI scan may differ between these new scanners and standard Anger cameras. Therefore, these new systems may require the determination of new normal limits to achieve optimal accuracy in relative myocardial perfusion quantification. Accurate diagnostic and prognostic results rivaling those obtained by expert readers can be obtained by this widely used technique.

SUMMARY

Throughout this review, we emphasize the importance of the different normal databases and the need for specific databases relative to distinct imaging procedures. use of appropriate normal limits allows optimal quantification of MPI by taking into account subtle image differences due to the hardware and software used, and the population studied.

A Novel Timesaving Method for Hepatobiliary Imaging for Suspected Acute Cholecystitis

OBJECTIVE

To optimize resource utilization of cholescintigraphy for suspected acute cholecystitis with a time-saving method without a loss in diagnostic accuracy.

MATERIALS AND METHODS

Institutional review board approval was obtained for this retrospective study. Hepatobiliary imaging data for 81 patients with suspected acute cholecystitis were recalled for modification into 2 summed static images, using only the first and last 5 minutes of the dynamic images, thereby eliminating the middle 50 minutes of imaging data. Two nuclear medicine physicians interpreted the summed images to assess visualization, and those interpretations were compared to the original reports based on using all 60 minutes of dynamic imaging. A third nuclear medicine physician mediated rare inter-reader interpretive disagreements. Comparison of interpretations of time-saving and conventional methods and also inter-observer variability was achieved using the Cohen κ coefficient analysis.

RESULTS

Interpretations rendered using the time-saving method showed near-perfect agreement with those based on the full dynamic imaging protocol (Cohen κ coefficient = 0.92 for both readers). Furthermore, nuclear medicine physician readers agreed with each other (Cohen κ coefficient = 0.95 between the 2 readers), indicating minimal inter-observer variability using this novel optimized technique.

CONCLUSION

In the setting of suspected acute cholecystitis, imaging resource utilization may be improved, via reduced gamma camera and technologist time, using a novel time-saving method without sacrificing diagnostic accuracy. Multicenter larger trials, however, will be necessary to establish reproducibility.

The Value of Attenuation Correction in Hybrid Cardiac SPECT/CT on Inferior Wall According to Body Mass Index

The purpose of this study was to evaluate the diagnostic value of attenuation-corrected single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) on the inferior wall compared to uncorrected (NC) SPECT MPI between obese and nonobese patients. A total of 157 consecutive patients (122 males and 35 females, with median age: 57.4 ± 11 years) who underwent AC technetium 99m-methoxyisobutylisonitrile (AC Tc99m-sestamibi) SPECT MPI were included to the study. A hybrid SPECT and transmission computed tomography (CT) system was used for the diagnosis with 1-day protocol, and stress imaging was performed first. During attenuation correction (AC) processing on a Xeleris Workstation using Myovation cardiac software with ordered subset expectation maximization (OSEM), iterative reconstruction with attenuation correction (IRAC) and NC images filtered back projection (FBP) were used. For statistical purposes, P < 0.05 was considered significant. This study included 73 patients with body mass index (BMI) <30 and 84 patients with BMI ≥ 30. In patients with higher BMI, increased amount of both visual and semiquantitative attenuation of the inferior wall was detected. IRAC reconstruction corrects the diaphragm attenuation of the inferior wall better than FBP. AC with OSEM iterative reconstruction significantly improves the diagnostic value of stress-only SPECT MPI in patients with normal weight and those who are obese, but the improvements are significantly greater in obese patients. Stress-only SPECT imaging with AC provides shorter and lower radiation exposure.

Advances in software for faster procedure and lower radiotracer dose myocardial perfusion imaging

The American Society of Nuclear Cardiology has recently published documents that encourage laboratories to take all the appropriate steps to greatly decrease patient radiation dose and has set the goal of 50% of all myocardial perfusion studies performed with an associated radiation exposure of 9mSv by 2014. In the present work, a description of the major software techniques readily available to shorten procedure time and decrease injected activity is presented. Particularly new reconstruction methods and their ability to include means for resolution recovery and noise regularization are described. The use of these improved reconstruction algorithms results in a consistent reduction in acquisition time, injected activity and consequently in the radiation dose absorbed by the patient. The clinical implications to the use of these techniques are also described in terms of maintained and even improved study quality, accuracy and sensitivity for the detection of heart disease.

Stress-only SPECT myocardial perfusion imaging: a review

Myocardial perfusion imaging (MPI) has enjoyed considerable success for decades due to its diagnostic accuracy and wealth of prognostic data. Despite this success several limitations such as lengthy protocols and radiation exposure remain. Advancements to address these shortcomings include abbreviated stress-only MPI (SO MPI) protocols, PET and both hardware and software methods to reduce radiation exposure and time. SO MPI has advantages in protocol time and radiation reduction with a wealth of supporting data in terms of diagnostic validity and prognostic value. Newer technologies such as attenuation correction, and advanced camera technologies have enabled SO MPI to be more efficient in reducing the time of acquisition and radiation dose and improving accuracy. This review examines the literature available, regarding accuracy, patient outcomes, implementation strategies, and newer developments associated with SO MPI.

Impact of SPECT myocardial perfusion imaging on cardiac care

Single photon emission computed tomography myocardial perfusion imaging is a powerful modality for the assessment of coronary artery disease. It is useful in the diagnosis of CAD, prognostication of CAD and the determination of viability. It acts as guide for therapy and has the ability to assess effectiveness of therapy. The use of SPECT myocardial perfusion imaging has also been shown to be cost-effective compared to other modalities in cardiology.

Diagnostic accuracy of high-resolution attenuation-corrected Anger-camera SPECT in the detection of coronary artery disease

BACKGROUND

There is limited data on diagnostic accuracy of recently introduced high-resolution Anger (HRA) SPECT incorporating attenuation correction (AC), noise reduction, and resolution recovery algorithms. We therefore studied 54 consecutive patients (excluding those with prior MI or cardiomyopathy) who had HRA-AC SPECT and coronary angiography (CA) ≤ 30 days and no change in symptoms.

METHODS

The HRA-AC studies were acquired in 128 × 128 matrix (3.2 mm pixel) format with simultaneous Gd-153 line-source AC. Measured variables were image quality, interpretive certainty, sensitivity and specificity for any CAD, sensitivity for single- and multivessel CAD, and the influence of gender, body mass index (BMI), and stress modality.

RESULTS

The mean age of the patients was 66 ± 11 years with a BMI of 32 ± 7 kg·m(-2). Mean interpretive certainty score was 2.7 on a 3-point scale and mean image quality score was 3.3 on a 4-point scale. Stress perfusion defects were detected in 34 of 38 patients with obstructive CAD [sensitivity 89%, 95% confidence interval (CI) 76%-95%]. The specificity was 75% (CI 51%-90%) and overall diagnostic accuracy was 85% (CI 73%-92%). Accuracy did not differ for females vs males, for BMI ≤30 vs >30, or for pharmacologic vs exercise SPECT. Sensitivity for single-vessel disease was 88% (CI 69%-96%) and for multivessel disease was 93% (CI 69%-99%).

CONCLUSION

New Anger technology incorporating innovative improvements results in high image quality with excellent interpretive certainty and high diagnostic accuracy.

Optimization of iterative reconstruction parameters with attenuation correction, scatter correction and resolution recovery in myocardial perfusion SPECT/CT

OBJECTIVE

The aim of this study was to characterize the optimal reconstruction parameters for ordered-subset expectation maximization (OSEM) with attenuation correction, scatter correction, and depth-dependent resolution recovery (OSEMACSCRR). We assessed the optimal parameters for OSEMACSCRR in an anthropomorphic torso phantom study, and evaluated the validity of the reconstruction parameters in the groups of normal volunteers and patients with abnormal perfusion.

METHODS

Images of the anthropomorphic torso phantom, 9 normal volunteers and 7 patients undergoing myocardial perfusion SPECT were acquired with a SPECT/CT scanner. SPECT data comprised a 64×64 matrix with an acquisition pixel size of 6.6 mm. A normalized mean square error (NMSE) of the phantom image was calculated to determine both optimal OSEM update and a full width at half maximum (FWHM) of Gaussian filter. We validated the myocardial count, contrast and noise characteristic for clinical subjects derived from OSEMACSCRR processing. OSEM with depth-dependent resolution recovery (OSEMRR) and filtered back projection (FBP) were simultaneously performed to compare OSEMACSCRR.

RESULTS

The combination of OSEMACSCRR with 90-120 OSEM updates and Gaussian filter with 13.2-14.85 mm FWHM yielded low NMSE value in the phantom study. When we used OSEMACSCRR with 120 updates and Gaussian filter with 13.2 mm FWHM in the normal volunteers, myocardial contrast showed significantly higher value than that derived from 120 updates and 14.85 mm FWHM. OSEMACSCRR with the combination of 90-120 OSEM updates and 14.85 mm FWHM produced lowest % root mean square (RMS) noise. Regarding the defect contrast of patients with abnormal perfusion, OSEMACSCRR with the combination of 90-120 OSEM updates and 13.2 mm FWHM produced significantly higher value than that derived from 90-120 OSEM updates and 14.85 mm FWHM. OSEMACSCRR was superior to FBP for the % RMS noise (8.52±1.08 vs. 9.55±1.71, p=0.02) and defect contrast (0.368±0.061 vs. 0.327±0.052, p=0.01), respectively.

CONCLUSIONS

Clinically optimized the number of OSEM updates and FWHM of Gaussian filter were (1) 120 updates and 13.2 mm, and (2) 90-120 updates and 14.85 mm on the OSEMACSCRR processing, respectively. Further assessment may be required to determine the optimal iterative reconstruction parameters in a larger patient population.

Comparison of attenuation, dual-energy-window, and model-based scatter correction of low-count SPECT to 82Rb PET/CT quantified myocardial perfusion scores

BACKGROUND

New reconstruction algorithms allow reduction in acquisition times or the amount of injected radioactivity. We examined the impact of different corrections on low-count clinical SPECT myocardial perfusion images (MPI) and compared to (82)Rb PET/CT. We compared no corrections (NC) to attenuation correction (AC) with and without scatter correction by either a dual-energy-window (AC-DEW) or model-based (AC-ESSE) approach. All reconstructions included resolution recovery.

METHODS

56 patients were imaged using a standard rest/stress Tc-99m-tetrofosmin MPI SPECT/CT protocol with an additional half-time acquisition. A (82)Rb-rest/stress PET/CT MPI was acquired within 4 weeks. Reconstruction methods were compared using summed rest/stress/difference scores from an objective algorithm (SRS/SSS/SDS).

RESULTS

The SRS and SSS for NC were significantly (P < .01) higher than for AC, but well correlated (r ≥ 0.87). The correlation in SRS/SSS among AC, AC-DEW, and AC-ESSE was excellent (r ≥ 0.98). AC-ESSE and AC-DEW had higher SRS (P ≤ .05) than AC, but the SDS values were not significantly different. Concordance with PET normal/abnormal classification was 76% for NC and ≥85% for the AC methods.

CONCLUSION

AC significantly improves the accuracy of low-count myocardial perfusion SPECT half-time imaging for the detection of disease compared to NC. Compared to PET, there was no significant difference among AC, AC-DEW, and AC-ESSE.

Initial multicentre experience of high-speed myocardial perfusion imaging: comparison between high-speed and conventional single-photon emission computed tomography with angiographic validation

PURPOSE

High-speed (HS) single-photon emission computed tomography (SPECT) with a recently developed solid-state camera shows comparable myocardial perfusion abnormalities to those seen in conventional SPECT. We aimed to compare HS and conventional SPECT images from multiple centres with coronary angiographic findings.

METHODS

The study included 50 patients who had sequential conventional SPECT and HS SPECT myocardial perfusion studies and coronary angiography within 3 months. Stress and rest perfusion images were visually analysed and scored semiquantitatively using a 17-segment model by two experienced blinded readers. Global and coronary territorial summed stress scores (SSS) and summed rest scores (SRS) were calculated. Global SSS ≥3 or coronary territorial SSS ≥2 was considered abnormal. In addition the total perfusion deficit (TPD) was automatically derived. TPD >5% and coronary territorial TPD ≥3% were defined as abnormal. Coronary angiograms were analysed for site and severity of coronary stenosis; ≥50% was considered significant.

RESULTS

Of the 50 patients, 13 (26%) had no stenosis, 22 (44%) had single-vessel disease, 6 (12%) had double-vessel disease and 9 (18%) had triple-vessel disease. There was a good linear correlation between the visual global SSS and SRS (Spearman's ρ 0.897 and 0.866, respectively; p < 0.001). In relation to coronary angiography, the sensitivities, specificities and accuracies of HS SPECT and conventional SPECT by visual assessment were 92% (35/38), 83% (10/12) and 90% (45/50) vs. 84% (32/38), 50% (6/12) and 76% (38/50), respectively (p < 0.001). The sensitivities, specificities and accuracies of HS SPECT and conventional SPECT in relation to automated TPD assessment were 89% (31/35), 57% (8/14) and 80% (39/49) vs. 86% (31/36), 77% (10/13) and 84% (41/49), respectively.

CONCLUSION

HS SPECT allows fast acquisition of myocardial perfusion images that correlate well with angiographic findings with overall accuracy by visual assessment better than conventional SPECT. Further assessment in a larger patient population may be needed to confirm this observation.

Clinical value of stress-only Tc-99m SPECT imaging: importance of attenuation correction

BACKGROUND

In selected patients, stress-only SPECT imaging has been proposed as an alternative to rest-stress SPECT imaging to improve laboratory efficiency and reduce radiation exposure. The impact of attenuation correction (AC) upon interpretation, post-test patient management and cardiac risk stratification in relation to stress-only imaging is not well understood.

OBJECTIVES

The purpose of this study was to determine the clinical value for laboratory throughput and predicting outcomes of normal and abnormal stress-only SPECT imaging with AC in a consecutive series of clinically referred patients.

METHODS

A retrospective analysis of 1,383 consecutive patients who were scheduled for stress-only SPECT imaging for symptom assessment of suspected myocardial ischemia was performed. All images had been interpreted and categorized using the standard 17-segment model without AC followed by AC. Follow-up data for 2.1 ± 1.3 years after SPECT imaging for the occurrence of cardiac events (non-fatal MI, cardiac death, and cardiac revascularization) previously collected by routine methods were reviewed.

RESULTS

Non-AC SPECT image interpretation revealed that 58% (802/1383) of patients had abnormal stress images. AC image interpretation of the abnormal non-AC images re-classified 83% (666/802) of these as normal. Among patients with abnormal stress images after AC (136/1383), 63% (86/136) returned for additional rest scans, while the remaining 37% (50/136) were clinically managed without further rest images. The incidence of cardiac death or non-fatal MI was very low in patients with normal stress-only scans (0.7%).

CONCLUSION

A strategy of stress-only imaging with AC in symptomatic patients is an efficient method which appropriately identifies at risk and low-risk patients yielding a low percentage requiring rest imaging. Clinical decisions can be made based on abnormal stress-only imaging without further rest imaging if clinically appropriate.

A multivendor phantom study comparing the image quality produced from three state-of-the-art SPECT-CT systems

OBJECTIVE

Ongoing advancements in single photon emission computed tomography with on-board X-ray computed tomography (SPECT-CT) hardware and software raise important questions regarding the relative performances of various cameras and their respective image-processing software. This phantom-based study compares images produced from three state-of-the-art cameras using four image quality measurements.

METHODS

A thorax phantom modeling the spine, lungs, a healthy heart, and three tumors (cylindrical bottles) was scanned using the following SPECT-CT systems: Philips' Precedence (PP), GE's Infinia-Hawkeye (GH), and Siemens' Symbia-T6 (SS). For each scan, Tc-99m solutions were injected into the heart, three bottles, and thorax to yield activity concentration ratios of roughly 6:1 for both heart:thorax and tumor:thorax. The data were reconstructed using the most advanced software available on the cameras, namely, Evolution for Bone and Evolution for Cardiac (EVB and EVC, respectively), Astonish (AST), and Flash3D (FLA) for GH, PP, and SS, respectively. In addition, all sets of data were reconstructed using our in-house software. The mean values of activity error, uniformity, signal-to-noise ratio, and contrast error were used as figures of merit (FOM).

RESULTS

No significant differences were observed for all FOM between all in-house reconstructions using PP, GH, and SS acquisition data. The mean activity error for the AST reconstruction (-24.0±1.6%) was significantly closer to the truth relative to EVB (-38.0±1.6%), EVC (-34.5±2.3%), and FLA (-33.8±1.6%). No significant differences were found between EVC and FLA for all FOM.

CONCLUSION

In this phantom-based study, Philips' AST provided the most quantitatively accurate and highest contrast images, whereas Siemens' FLA and GE's EVC provided relatively higher signal-to-noise ratios and more uniform images.

Advances in nuclear cardiac instrumentation with a view towards reduced radiation exposure

Recent advances in nuclear cardiology instrumentation have enabled myocardial perfusion imaging (MPI) with improved image quality and faster scan times. These developments also can be exploited to reduce the effective radiation dose to the patient. In this review, we discuss these technologies including new single photon emission computed tomography (SPECT) and positron emission tomography (PET) scanners, as well as novel reconstruction software with regard to their potential for the reduction of the patient radiation dose. New advances in nuclear cardiology instrumentation will allow routine rest/stress MPI imaging with low radiation doses (<5 mSv) and fast imaging times, even by the software-only solutions. It is possible to further reduce the MPI radiation dose to less than 2 to 3 mSv range with standard acquisition times. PET perfusion imaging also can be performed with very low doses especially by the three-dimensional scanners allowing hybrid PET/computed tomographic angiography (CTA) imaging with low overall dose. In addition, stress-only protocols can be utilized to further reduce the radiation dose and the overall test time.

Review of radiation reduction strategies in clinical cardiovascular imaging

The use of ionizing radiation for medical diagnostic tests and interventional procedures has grown substantially over the past 2 decades, and there is now considerable concern expressed in both the medical literature and the lay press of the harmful effects of radiation exposure. Although there is some controversy regarding whether this medical radiation is actually harmful, minimizing the dose to the patient is logical and a basic part of proper care. To do this, clinicians must have an understanding of the amount of radiation that is involved with each test. Physicians have a responsibility to keep the level of radiation exposure as low as reasonably achievable. A number of simple and common sense measures can help achieve this goal. Encouragingly, there are also numerous new technologies which can substantially lower radiation dose, especially in cardiovascular studies. This review will highlight various ways to reduce radiation in cardiovascular imaging.