Recent advances and future trends in multimodality cardiac imaging

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.

Nitrido Technetium-99 m Core in Radiopharmaceutical Applications: Four Decades of Research

The knowledge on element 43 (Tc) of the periodic table, built over the years through the contributions given by the close relationship between chemistry and nuclear medicine, allowed the development of new and increasingly effective radiopharmaceuticals useful both as perfusion and target specific imaging agents for SPECT (single photon emission tomography). Among the manifold Tc-compounds, Tc(V) nitrido complexes played a relevant role in the search for new technetium-99m radiopharmaceuticals, providing efficient labeling procedures that can be conveniently exploited for the design and synthesis of agents, also incorporating small organic molecules or peptides having defined structural features. With this work, we present an overview of four decades of research on the chemistry and on the nuclear medicine applications of Tc(V) nitrido complexes.

68Ga-Galmydar: A PET imaging tracer for noninvasive detection of Doxorubicin-induced cardiotoxicity

Background

Cancer patients undergoing Doxorubicin (DOX) treatment are susceptible to acute and chronic cardiac anomalies, including aberrant arrhythmias, ventricular dysfunction, and heart failure. To stratify patients at high risk for DOX -related heart failure (CHF), diagnostic techniques have been sought. While echocardiography is used for monitoring LVEF and LV volumes due to its wide-availability and cost-efficiency, it may not identify early stages of the initiation of DOX-induced systolic heart failure. To address these limitations, PET tracers could also provide noninvasive assessment of early and reversible metabolic changes of the myocardium.

Objective

Herein, we report a preliminary investigation of ⁶⁸Ga-Galmydar potential to monitor Dox-induced cardiomyopathy in vivo, ex vivo, and in cellulo employing both nuclear- and optical imaging.

Methods and results

To assess ⁶⁸Ga-Galmydar ability for monitoring DOX-induced cardiomyopathy, microPET imaging was performed 5 d post treatment of rats either with a single dose of DOX (15 mg/kg) or vehicle as a control (saline) and images were co-registered for anatomical reference using CT. Following tail-vein injection of the radiotracer in rats at 60 min, micro-PET/CT static scan (10 min acquisition), ⁶⁸Ga-Galmydar demonstrated 1.91-fold lower uptake in hearts of DOX-treated (standard uptake value; SUV: 0.92, n = 3) rats compared with their vehicle treated (SUV: 1.76, n = 3) control counterparts. For correlation of PET imaging data, post-imaging quantitative biodistribution studies were also performed, wherein excised organs were counted for γ activity, and normalized to injected dose. The post imaging pharmacokinetic data also demonstrated heart uptake values of 2.0 fold lower for DOX treated rats(%ID/g; DOX: 0.44 ± 0.1, n = 3) compared to their vehicle-treated controls (%ID/g; Control: 0.89 ± 0.03, n = 3, p = 0.04). Employing the fluorescent traits of Galmydar, live cell fluorescence imaging indicated a gradual decrease in uptake and retention of Galmydar within mitochondria of H9c2 cells following DOX-treatment, while indicating dose-dependent and time-dependent uptake profiles. Following depolarization of electronegative transmembrane gradients at the mitochondrial membrane, the uptake of the probe was decreased in H9c2 cells, and the uptake profiles were found to be identical, using both fluorescence and radiotracer bioassays. Finally, the decreased uptake of the metalloprobe in H9c2 cells also correlated with caspase-3 expression resulting from DOX-induced cardiotoxicity and cell death.

Conclusions

⁶⁸Ga-Galmydar could provide a noninvasive assessment of DOX-related and likely reversible metabolic changes at earliest stages. Further studies with other chemotherapeutics (potentially capable of inducing cardiomyopathy) are underway.

Assessment of atherosclerotic plaque calcification using F18-NaF PET-CT

BACKGROUND

The aim of the present study was to evaluate the uptake of F18-NaF by the arterial wall in patients with high cardiovascular (CV) risk profile. The tracer uptake was assessed in relation to gender and the number of CV risk factors.

METHODS AND RESULTS

25 patients without known CV disease were included and evaluated by PET-CT with F18-NaF: 14 (56%) men and 11 (44%) women. The mean target-to-background ratio (TBR: max SUV/mean blood-pool SUV) but not the corrected uptake per lesion (CUL: max SUV - mean blood-pool SUV) was higher in men than women (TBR: 1.8 ± 0.6 vs 1.7 ± 0.2; P = 0.04; CUL: 0.7 ± 0.3 vs W 0.6 ± 0.1; P = 0.4). Patients with >3 CV risk factors had higher CUL (0.8 ± 0.1 vs 0.6 ± 0.2; P = 0.01) but not TBR (1.8 ± 0.2 vs 1.7 ± 0.6; P = 0.7) than patients with <3 risk factors.

CONCLUSIONS

The TBR but not CUL is higher in men than women while the CUL but not TBR is related to the number of CV risk factors. These results are hypothesis-generating and require validation in larger studies.

A generator-produced gallium-68 radiopharmaceutical for PET imaging of myocardial perfusion

Lipophilic cationic technetium-99m-complexes are widely used for myocardial perfusion imaging (MPI). However, inherent uncertainties in the supply chain of molybdenum-99, the parent isotope required for manufacturing ⁹⁹Mo/^99mTc generators, intensifies the need for discovery of novel MPI agents incorporating alternative radionuclides. Recently, germanium/gallium (Ge/Ga) generators capable of producing high quality ⁶⁸Ga, an isotope with excellent emission characteristics for clinical PET imaging, have emerged. Herein, we report a novel ⁶⁸Ga-complex identified through mechanism-based cell screening that holds promise as a generator-produced radiopharmaceutical for PET MPI.

Defining characteristics of early adopters of multimodality cardiovascular imaging

BACKGROUND

The prototype for the cardiovascular imager has evolved to necessitate some degree of competency in multimodality imaging (MMI)-defined as expertise in at least 2 of the 4 modalities (echocardiography [ECHO], nuclear cardiology [NUC], cardiovascular computed tomography [CCT], and magnetic resonance [CMR]). Uncertainty exists about the effects of this change.

METHODS

Information detailing the current totals of board-certified practitioners in MMI was collected and organized into groups of 1, 2, and 3 modalities. A randomized stratified sample of names was obtained to identify a representative 10% of each group. Those names were cross-referenced online with information from state medical boards, faculty rosters of academic medical centers, and physician tracking Websites.

RESULTS

There are a total of 2209 board-certified MMI practitioners (2 modalities = 1885, 3 modalities = 324) and 6450 single-modality imagers in the United States. Of those sampled, 98.9% were cardiologists, 31.3% were at academic medical centers and mean time from medical school graduation was 17.75 years. MMI practitioners were more likely to have graduated from medical school more recently (P < 0.0001) and to be trained cardiologists (P = 0.003) than those who practice in a single modality. There was a nonsignificant trend toward MMI being practiced more commonly in an academic setting (P = 0.38).

CONCLUSION

Board-certified specialists in MMI tend to be younger cardiologists than those engaged in single-modality cardiac imaging. There are few advanced (3 modality) MMI practitioners in the United States.

Multimodality image fusion for diagnosing coronary artery disease

Coronary artery disease (CAD) is one of the leading causes of death in the US and a substantial health-care burden in all industrialized societies. In recent years we have witnessed a constant strive towards the development and the clinical application of novel or improved detection methods as well as therapies. Particularly, noninvasive imaging is a decisive component in the cardiovascular field. Image fusion is the ability of combining into a single integrated display the anatomical as well as the physiological data retrieved by separated modalities. Clinical evidence suggests that it represents a promising strategy in CAD assessment and risk stratification by significantly improving the diagnostic power of each modality independently considered and of the traditional side-by-side interpretation. Numerous techniques and approaches taken from the image registration field have been implemented and validated in the context of CAD assessment and management. Although its diagnostic power is widely accepted, additional technical developments are still needed to become a routinely used clinical tool.

The use and importance of liposomes in positron emission tomography

Among different imaging modalities, Positron Emission Tomography (PET) gained importance in routine hospital practice depending on ability to diagnose diseases in early stages and tracing of therapy by obtaining metabolic information. The combination of PET with Computed Tomography (CT) forms hybrid imaging modality that gives chance to obtain better images having higher resolution by fusing both functional and anatomical images in the same imaging modality at the same time. Therefore, better contrast agents are essentially needed. The advance in research about developing drug delivery systems as specific nanosized targeted systems gained an additional importance for obtaining better diagnosis and therapy of different diseases. Liposomes appear to be more attractive drug delivery systems in delivering either drugs or imaging ligands to target tissue or organ of diseases with higher accumulation by producing in nano-scale, long circulating by stealth effect and specific targeting by modifying with specific ligands or markers. The combination of positron emitting radionuclides with liposomes are commonly in research level nowadays and there is no commercially available liposome formulation for PET imaging. However by conjugating positron emitter radionuclide with liposomes can form promising diagnostic agents for improved diagnosis and following up treatments by increasing image signal/contrast in the target tissue in lower concentrations by specific targeting as the most important advantage of liposomes. More accurate and earlier diagnosis of several diseases can be obtained even in molecular level with the use of stable and effectively radiolabeled molecular target specific nano sized liposomes with longer half-lived positron emitting radionuclides.

Quantitative cardiac positron emission tomography: the time is coming!

In the last 20 years, the use of positron emission tomography (PET) has grown dramatically because of its oncological applications, and PET facilities are now easily accessible. At the same time, various groups have explored the specific advantages of PET in heart disease and demonstrated the major diagnostic and prognostic role of quantitation in cardiac PET. Nowadays, different approaches for the measurement of myocardial blood flow (MBF) have been developed and implemented in user-friendly programs. There is large evidence that MBF at rest and under stress together with the calculation of coronary flow reserve are able to improve the detection and prognostication of coronary artery disease. Moreover, quantitative PET makes possible to assess the presence of microvascular dysfunction, which is involved in various cardiac diseases, including the early stages of coronary atherosclerosis, hypertrophic and dilated cardiomyopathy, and hypertensive heart disease. Therefore, it is probably time to consider the routine use of quantitative cardiac PET and to work for defining its place in the clinical scenario of modern cardiology.

Hybrid image visualization tool for 3D integration of CT coronary anatomy and quantitative myocardial perfusion PET

PURPOSE

Multimodal cardiac imaging by CTA and quantitative PET enables acquisition of patient-specific coronary anatomy and absolute myocardial perfusion at rest and during stress. In the clinical setting, integration of this information is performed visually or using coronary arteries distribution models. We developed a new tool for CTA and quantitative PET integrated 3D visualization, exploiting XML and DICOM clinical standards.

METHODS

The hybrid image tool (HIT) developed in the present study included four main modules: (1) volumetric registration for spatial matching of CTA and PET data sets, (2) an interface to PET quantitative analysis software, (3) a derived DICOM generator able to build DICOM data set from quantitative polar maps, and (4) a 3D visualization tool of integrated anatomical and quantitative flow information. The four modules incorporated in the HIT tool communicate by defined standard XML files: XML-transformation and XML MIST standards.

RESULTS

The HIT tool implements a 3D representation of CTA showing real coronary anatomy fused to PET-derived quantitative myocardial blood flow distribution. The technique was validated on 16 data sets from EVINCI study population. The validation of the method confirmed the high matching between "original" and derived data sets as well as the accuracy of the registration procedure.

CONCLUSIONS

Three-dimensional integration of patient- specific coronary artery anatomy provided by CTA and quantitative myocardial blood flow obtained from PET imaging can improve cardiac disease assessment. The HIT tool introduced in this paper may represent a significant advancement in the clinical use of this multimodal approach.

Cardiac MR perfusion image processing techniques: a survey

First-pass cardiac MR perfusion (CMRP) imaging has undergone rapid technical advancements in recent years. Although the efficacy of CMRP imaging in the assessment of coronary artery diseases (CAD) has been proven, its clinical use is still limited. This limitation stems, in part, from manual interaction required to quantitatively analyze the large amount of data. This process is tedious, time-consuming, and prone to operator bias. Furthermore, acquisition and patient related image artifacts reduce the accuracy of quantitative perfusion assessment. With the advent of semi- and fully automatic image processing methods, not only the challenges posed by these artifacts have been overcome to a large extent, but a significant reduction has also been achieved in analysis time and operator bias. Despite an extensive literature on such image processing methods, to date, no survey has been performed to discuss this dynamic field. The purpose of this article is to provide an overview of the current state of the field with a categorical study, along with a future perspective on the clinical acceptance of image processing methods in the diagnosis of CAD.