New Trends in Camera and Software Technology in Nuclear Cardiology

Technological Advances in SPECT and SPECT/CT Imaging

Single photon emission tomography/computed tomography (SPECT/CT) is a mature imaging technology with a dynamic role in the diagnosis and monitoring of a wide array of diseases. This paper reviews the technological advances, clinical impact, and future directions of SPECT and SPECT/CT imaging. The focus of this review is on signal amplifier devices, detector materials, camera head and collimator designs, image reconstruction techniques, and quantitative methods. Bulky photomultiplier tubes (PMTs) are being replaced by position-sensitive PMTs (PSPMTs), avalanche photodiodes (APDs), and silicon PMs to achieve higher detection efficiency and improved energy resolution and spatial resolution. Most recently, new SPECT cameras have been designed for cardiac imaging. The new design involves using specialised collimators in conjunction with conventional sodium iodide detectors (NaI(Tl)) or an L-shaped camera head, which utilises semiconductor detector materials such as CdZnTe (CZT: cadmium-zinc-telluride). The clinical benefits of the new design include shorter scanning times, improved image quality, enhanced patient comfort, reduced claustrophobic effects, and decreased overall size, particularly in specialised clinical centres. These noticeable improvements are also attributed to the implementation of resolution-recovery iterative reconstructions. Immense efforts have been made to establish SPECT and SPECT/CT imaging as quantitative tools by incorporating camera-specific modelling. Moreover, this review includes clinical examples in oncology, neurology, cardiology, musculoskeletal, and infection, demonstrating the impact of these advancements on clinical practice in radiology and molecular imaging departments.

Successful innovation: A time for change?

Innovation plays an important role in the advancement of nuclear cardiology, meeting the need for reduced exposure to radiation, and maintaining and improving image quality. As we innovate, it is important to understand the impact of these improvements on the clinical and research knowledge base that has made nuclear cardiology such a powerful clinical tool. The need for comparative studies insuring stability in the clinical applicability of our current guidelines and use of the prognostic power of radionuclide myocardial perfusion imaging in clinical practice is essential for new and innovative techniques. The existing data demonstrating the significant differences that can occur with the innovative techniques is explored. The need for tools to insure comparable data is available as we begin to utilize registries to inform our clinical practice and research will be an important part of the future of nuclear cardiology.

Proceedings of the cardiac PET summit meeting 12 may 2014: Cardiac PET and SPECT instrumentation

Advances in PET and SPECT and imaging hardware and software are vastly improving the noninvasive evaluation of myocardial perfusion and function. PET perfusion imaging has benefitted from the introduction of novel detectors that now allow true 3D imaging, and precise attenuation correction (AC). These developments have also resulted in perfusion images with higher spatial and contrast resolution that may be acquired in shorter protocols and/or with less patient radiation exposure than traditional PET or SPECT studies. Hybrid PET/CT cameras utilize transmission computed tomographic (CT) scans for AC, and offer the additional clinical advantages of evaluating coronary calcium and myocardial anatomy but at a higher cost than PET scanners that use (68)Ge radioactive line sources. As cardiac PET systems continue to improve, dedicated cardiac SPECT systems are also undergoing a profound change in their design. The scintillation camera general purpose design is being replaced with systems with multiple detectors focused on the heart yielding 5 to 10 times the sensitivity of conventional SPECT. As a result, shorter acquisition times and/or lower tracer doses produce higher quality SPECT images than were possible before. This article reviews these concepts and compares the attributes of PET and SPECT instrumentation.

Beyond ultrasound: advances in multimodality cardiac imaging

The rapid technological evolution accomplished in noninvasive cardiac imaging techniques over the past few decades has provided physicians with a large armamentarium for the evaluation of patients with known or suspected coronary heart disease. Noninvasive assessment of coronary artery calcium or noninvasive coronary angiography may be performed using computed tomography or magnetic resonance imaging. These techniques evaluate the presence of atherosclerosis rather than ischemia. Conversely, nuclear cardiology is the most widely used noninvasive approach for the assessment of myocardial perfusion and function. These techniques coupled with the development of dedicated image fusion software packages to merge data sets from different modalities have paved the way for hybrid imaging. This article provides a description of the available noninvasive imaging techniques in the assessment of coronary anatomy, myocardial perfusion, and cardiac function in patients with known or suspected coronary heart disease.

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.

Cumulative radiation dose from medical imaging in chronic adult patients

Chronic patients require ongoing care that results in repeated imaging and exposure to ionizing radiation for both diagnostic and therapeutic purposes. This is of concern due to the long-term effects of radiation exposure, namely the association between radiation and increased cancer risk. In this study, the scientific literature on cumulated dose of radiation accrued from medical imaging by 4 cohorts of chronic patients (cardiac disease, end-stage kidney disease, inflammatory bowel disease, and patients undergoing endovascular aortic repair) was systematically reviewed. We found that the cumulative effective dose is moderate in cardiac and inflammatory bowel disease patients, high in end-stage kidney disease patients, and very high in endovascular aortic repair patients. We concluded that radiation burden of medical imaging is high in selected cohorts of chronic patients. Efforts should be implemented to reduce this cumulative dose and its potential attendant risks.

A tailored ML-EM algorithm for reconstruction of truncated projection data using few view angles

Dedicated cardiac single photon emission computed tomography (SPECT) systems have the advantage of high speed and sensitivity at no loss, or even a gain, in resolution. The potential drawbacks of these dedicated systems are data truncation by the small field of view (FOV) and the lack of view angles. Serious artifacts, including streaks outside the FOV and distortion in the FOV, are introduced to the reconstruction when using the traditional emission data maximum-likelihood expectation-maximization (ML-EM) algorithm to reconstruct images from the truncated data with a small number of views. In this note, we propose a tailored ML-EM algorithm to suppress the artifacts caused by data truncation and insufficient angular sampling by reducing the image updating step sizes for the pixels outside the FOV. As a consequence, the convergence speed for the pixels outside the FOV is decelerated. We applied the proposed algorithm to truncated analytical data, Monte Carlo simulation data and real emission data with different numbers of views. The computer simulation results show that the tailored ML-EM algorithm outperforms the conventional ML-EM algorithm in terms of streak artifacts and distortion suppression for reconstruction from truncated projection data with a small number of views.

Physical attributes, limitations, and future potential for PET and SPECT

Advances in SPECT and PET imaging hardware, software, and radiotracers are vastly improving the non-invasive evaluation of myocardial perfusion and function. In contrast to traditional dual-headed, sodium iodide crystal and photomultiplier cameras with mechanical collimators, new SPECT camera designs utilize novel, collimators, and solid-state detectors that convert photons directly to electrical signals. These cameras simultaneously collect data from as many as 76 small detectors narrowly focused on the heart. New noise regularization and resolution recovery/noise reduction reconstruction software interprets emitted counts more efficiently and thus more effectively discriminates between useful signals and noise. As a result, shorter acquisition times and/or lower tracer doses produce higher quality SPECT images than were possible before. PET perfusion imaging has benefitted from the introduction of novel detectors that now allow true 3D imaging, new radiopharmaceuticals, and precise attenuation correction (AC). These developments have resulted in perfusion images with higher spatial and contrast resolution that may be acquired in shorter protocols and/or with less patient radiation exposure than traditional SPECT. Hybrid SPECT/CT and PET/CT cameras utilize transmission computed tomographic (CT) scans for AC, and offer the additional clinical advantages of evaluating coronary calcium, myocardial anatomy (including non-invasive CT angiography), myocardial function, and myocardial perfusion in a single imaging procedure.

Incremental prognostic value of coronary flow reserve assessed with single-photon emission computed tomography

BACKGROUND

We assessed the prognostic value of coronary flow reserve (CFR) estimated by single-photon emission computed tomography (SPECT) in patients with suspected myocardial ischemia.

METHODS AND RESULTS

Myocardial perfusion and CFR were assessed in 106 patients using dipyridamole/rest Tc-99m sestamibi SPECT and follow-up was obtained in 103 (97%) patients. Four early revascularized patients were excluded and 99 were assigned to normal (summed stress score <3) vs abnormal myocardial perfusion and to normal (≥2.0) vs abnormal CFR. During the follow-up (5.8 ± 2.1 years), 28 patients experienced a cardiac event (cardiac death, nonfatal myocardial infarction, and late revascularization). Abnormal perfusion (P < .01) and abnormal CFR (P < .05) were independent predictors of cardiac events at Cox proportional hazard regression analysis. Also in patients with normal perfusion, abnormal CFR was associated with a higher annual event rate compared with normal CFR (5.2% vs 0.7%; P < .05). CFR data improved the prognostic power of the model including clinical and myocardial perfusion data increasing the global chi-square from 18.6 to 22.8 (P < .05). Finally, at parametric survival analysis, in patients with normal perfusion the time to achieve ≥2% risk of events was >60 months in those with normal and <12 months in those with abnormal CFR.

CONCLUSIONS

Myocardial perfusion findings and CFR at SPECT imaging are both independent predictors of cardiac events. Estimated CFR provides incremental prognostic information over those obtained from clinical and myocardial perfusion data, particularly in patients with normal perfusion findings.

What are the basic concepts of temporal, contrast, and spatial resolution in cardiac CT?

An imaging instrument can be characterized by its spatial resolution, contrast resolution, and temporal resolution. The capabilities of computed tomography (CT) relative to other cardiac imaging modalities can be understood in these terms. The purpose of this review is to characterize the spatial, contrast, and temporal resolutions of cardiac CT in practical terms.