What Is New in Risk Assessment in Nuclear Cardiology?

Nuclear cardiology techniques allow in-depth evaluation of cardiac patients. A body of literature has established the use of nuclear cardiology. The results obtained with traditional cameras have been reinforced by those obtained with a series of innovations that have revolutionized the field of nuclear cardiology. This article highlights the role of nuclear cardiology in the risk assessment of patients with cardiac disease and sheds light on advancements of nuclear imaging techniques in the cardiovascular field. Patient risk stratification has a key role in modern precision medicine. Nuclear cardiac imaging techniques may quantitatively investigate major disease mechanisms of different cardiac pathologies.

Simultaneous assessment of myocardial perfusion and adrenergic innervation in patients with heart failure by low-dose dual-isotope CZT SPECT imaging

BACKGROUND

In patients with heart failure (HF) sequential imaging studies have demonstrated a relationship between myocardial perfusion and adrenergic innervation. We evaluated the feasibility of a simultaneous low-dose dual-isotope 123I/99mTc-acquisition protocol using a cadmium-zinc-telluride (CZT) single-photon emission computed tomography (SPECT) camera.

METHODS AND RESULTS

Thirty-six patients with HF underwent simultaneous low-dose 123I-metaiodobenzylguanidine (MIBG)/99mTc-sestamibi gated CZT-SPECT cardiac imaging. Perfusion and innervation total defect sizes and perfusion/innervation mismatch size (defined by 123I-MIBG defect size minus 99mTc-sestamibi defect size) were expressed as percentages of the total left ventricular (LV) surface area. LV ejection fraction (EF) significantly correlated with perfusion defect size (P < .005), innervation defect size (P < .005), and early (P < .05) and late (P < .01) 123I-MIBG heart-to-mediastinum (H/M) ratio. In addition, late H/M ratio was independently associated with reduced LVEF (P < .05). Although there was a significant relationship (P < .001) between perfusion and innervation defect size, innervation defect size was larger than perfusion defect size (P < .001). At multivariable linear regression analysis, 123I-MIBG washout rate (WR) correlated with perfusion/innervation mismatch (P < .05).

CONCLUSIONS

In patients with HF, a simultaneous low-dose dual-isotope 123I/99mTc-acquisition protocol is feasible and could have important clinical implications.

Cardiac 123I-mIBG Imaging in Heart Failure

Cardiac sympathetic upregulation is one of the neurohormonal compensation mechanisms that play an important role in the pathogenesis of chronic heart failure (CHF). In the past decades, cardiac ¹²³I-mIBG scintigraphy has been established as a feasible technique to evaluate the global and regional cardiac sympathetic innervation. Although cardiac ¹²³I-mIBG imaging has been studied in many cardiac and neurological diseases, it has extensively been studied in ischemic and non-ischemic CHF. Therefore, this review will focus on the role of ¹²³I-mIBG imaging in CHF. This non-invasive, widely available technique has been established to evaluate the prognosis in CHF. Standardization, especially among various combinations of gamma camera and collimator, is important for identifying appropriate thresholds for adequate risk stratification. Interestingly, in contrast to the linear relationship between ¹²³I-mIBG-derived parameters and overall prognosis, there seems to be a “bell-shape” curve for ¹²³I-mIBG-derived parameters in relation to ventricular arrhythmia or appropriate implantable cardioverter defibrillator (ICD) therapy in patients with ischemic CHF. In addition, there is a potential clinical role for cardiac ¹²³I-mIBG imaging in optimizing patient selection for implantation of expensive devices such as ICD and cardiac resynchronization therapy (CRT). Based on cardiac ¹²³I-mIBG data risk models and machine learning, models have been developed for appropriate risk assessment in CHF.

Cardiac sympathetic dysfunction in left ventricular hypertrophy caused by arterial hypertension and degenerative aortic stenosis

BACKGROUND

To evaluate cardiac sympathetic innervation in hypertensive patients with left ventricular (LV) hypertrophy (H) and aortic stenosis (AS) submitted to transcatheter aortic valve implantation (TAVI).

METHODS AND RESULTS

Twenty-two hypertensive elders (82 ± 5 years) with severe AS and significant LVH (> 122 g·m-2 in women and > 149 g·m-2 in men) were compared with 14 patients with uncomplicated essential hypertension (HT) with similar degree of LVH and 10 controls. 123I-metaiodobenzylguanidine (MIBG) and 99mTc-tetrofosmin SPECT acquisitions were obtained to assess sympathetic innervation and LV perfusion. The innervation/perfusion mismatch score was taken as an indicator of cardiac sympathetic dysfunction. The imaging protocol was repeated 6 months after TAVI. Regional MIBG uptake was more heterogeneous in HT and AS patients than controls, and therefore, innervation/perfusion mismatch score was higher in both AS (9 ± 8) and HT (5 ± 2) than controls (1 ± 1, P < .001). On multivariate analysis, significant LVH was the major predictor of impaired LV sympathetic innervation (OR 19.45, 95% CI 1.87-201.92; P = .013). After TAVI, no differences in measures of LV sympathetic innervation were evident, although only a marginal LV mass reduction was observed (- 5.4 ± 2.4 g).

CONCLUSIONS

Cardiac sympathetic innervation is impaired in patients with LVH, either with AS or not, and is not impacted significantly by TAVI procedure.

40 Years Anniversary of Cardiac 123I-mIBG Imaging: State of the Heart

Purpose of Review

This narrative review reflects on the body of evidence on cardiac 123I-mIBG imaging that has accumulated since the introduction in the late 1970s and focusses on to what extent cardiac 123I-mIBG imaging has fulfilled its potential in cardiology especially.

Recent Findings

In contrast to the linear relationship between 123I-mIBG-derived parameters and overall prognosis in heart failure, there seems a “bell-shape” curve for 123I-mIBG-derived parameters and arrhythmic events. In addition, there is a potential clinical role for cardiac 123I-mIBG in optimizing patient selection for expensive devices (i.e., ICD and CRT). This needs of course to be established in future trials.

Summary

Cardiac 123I-mIBG imaging is, despite the numerous of studies, sometimes mistakenly seen as a nice to have technique rather than a must have imaging modality. Although cardiac 123I-mIBG imaging has grown and matured over the years, its full clinical potential has still not been tested to the maximum.

The role of myocardial innervation imaging in different clinical scenarios: an expert document of the European Association of Cardiovascular Imaging and Cardiovascular Committee of the European Association of Nuclear Medicine

Cardiac sympathetic activity plays a key role in supporting cardiac function in both health and disease conditions, and nuclear cardiac imaging has always represented the only way for the non-invasive evaluation of the functional integrity of cardiac sympathetic terminals, mainly through the use of radiopharmaceuticals that are analogues of norepinephrine and, in particular, with the use of 123I-mIBG imaging. This technique demonstrates the presence of cardiac sympathetic dysfunction in different cardiac pathologies, linking the severity of sympathetic nervous system impairment to adverse patient's prognosis. This article will outline the state-of-the-art of cardiac 123I-mIBG imaging and define the value and clinical applications in the different fields of cardiovascular diseases.

Multi-Modality Imaging for the Identification of Arrhythmogenic Substrates Prior to Electrophysiology Studies

Noninvasive cardiac imaging is crucial for the characterization of patients who are candidates for cardiac ablations, for both procedure planning and long-term management. Multimodality cardiac imaging can provide not only anatomical parameters but even more importantly functional information that may allow a better risk stratification of cardiac patients. Moreover, fusion of anatomical and functional data derived from noninvasive cardiac imaging with the results of endocavitary mapping may possibly allow a better identification of the ablation substrate and also avoid peri-procedural complications. As a result, imaging-guided electrophysiological procedures are associated with an improved outcome than traditional ablation procedures, with a consistently lower recurrence rate.

Cardio-pulmonary involvement in pulmonary arterial hypertension: A perfusion and innervation scintigraphic evaluation

BACKGROUND

Pulmonary arterial hypertension (PAH) is characterized by the right ventricle (RV) remodeling and pulmonary endothelial dysfunction. We studied cardiac perfusion and innervation in PAH with a cadmium-zinc-telluride (CZT) scanner and lung uptake impairment of 123I-metaiodobenzylguanidine (123I-MIBG).

METHODS

In 13 patients with newly diagnosed PAH and 11 dilated cardiomyopathies (DCM, for comparative purposes), we assessed early and delayed 123I-MIBG uptake ratios of lung-to-mediastinum (L/M) and heart-to-mediastinum (H/M) on anterior planar images. A quantitative myocardial innervation with 123I-MIBG and perfusion with 99mTc-tetrofosmin using CZT-SPECT was performed. All patients underwent right heart catheterization.

RESULTS

Early and delayed L/M ratios in PAH were lower than DCM (1.47 ± 0.14 vs 1.98 ± 0.11 and 1.40 ± 0.13 vs 1.83 ± 0.09; P < .001), while early and delayed H/M were impaired but not different (1.73 ± 0.20 vs 1.65 ± 0.18 and 1.73 ± 0.27 vs 1.58 ± 0.19). RV perfusion and early innervation were significantly higher in PAH compared to DCM (68.4 ± 13.4 vs 28.6 ± 4.1 and 58.8 ± 9.3 vs 27 ± 2.2; P < .001); delayed RV innervation was not evaluable. RV/LV perfusion and innervation ratios were significantly related (R = 0.74; P < .0001) and had a significant correlation with clinical, hemodynamic, and morpho-functional parameters, including L/M ratios.

CONCLUSION

Cardio-pulmonary scintigraphy through a perfusion and innervation study is feasible and may identify pulmonary vascular and RV remodeling, as in PAH.

Cardiac sympathetic denervation in wild-type transthyretin amyloidosis

BACKGROUND

Tissue accumulation of misfolded transthyretin (TTR) may occur because of TTR gene mutations (variant amyloid TTR amyloidosis, ATTRv), or as an age-related phenomenon (wild-type ATTR, ATTRwt). Cardiac sympathetic denervation has been reported in ATTRv, but has never been investigated in ATTRwt.

METHODS

Fifteen consecutive patients with ATTRwt cardiomyopathy (81% men, median age 82 years, no one with prior myocardial infarction) underwent Cadmium Zinc Telluride tomographic imaging for amyloid burden (^99mTc-hydroxymethylene diphosphonate - ^99mTc-HMDP), innervation (¹²³I-metaiodobenzylguanidine - ¹²³I-MIBG), and perfusion (^99mTc-tetrofosmin).

RESULTS

Median summed ^99mTc-HMDP score was 60 (58-62), denoting a severe and diffuse amyloid burden. Planar ¹²³I-MIBG examination showed decreased early and late H/M ratios (late H/M ratio: 1.5 [1.3-1.6], range 1.2-1.9, reference value ≥2.0). Summed ¹²³I-MIBG score was 12 (6-22), with the most prominent denervation in the infero-septal, inferior, and infero-lateral regions; summed rest score was 7 (5-11), with lowest degrees of myocardial perfusion in the inferior and infero-septal regions. The correlation between amyloid burden (as relative ^99mTc-HMDP uptake) and innervation (as relative ¹²³I-MIBG uptake) did not achieve statistical significance at both segmental (p = .252) and regional level (p = .251). Nevertheless, denervation tended to worsen in parallel with the amyloid burden, and ¹²³I-MIBG scores increased with ^99mTc-HMDP scores. Segments and regions with prominent hypoperfusion also showed a higher degree of denervation (r = 0.500 and 0.591, respectively; both p < .001).

CONCLUSIONS

Patients with ATTRwt cardiomyopathy display cardiac sympathetic denervation, particularly in the inferior and septal myocardial wall. Myocardial hypoperfusion has a similar regional pattern, while the amyloid burden is more extensive.

Cardiac Imaging With 123I-meta-iodobenzylguanidine and Analogous PET Tracers: Current Status and Future Perspectives

Autonomic innervation plays an important role in proper functioning of the cardiovascular system. Altered cardiac sympathetic function is present in a variety of diseases, and can be assessed with radionuclide imaging using sympathetic neurotransmitter analogues. The most studied adrenergic radiotracer is cardiac ¹²³I-meta-iodobenzylguanidine (¹²³I-mIBG). Cardiac ¹²³I-mIBG uptake can be evaluated using both planar and tomographic imaging, thereby providing insight into global and regional sympathetic innervation. Standardly assessed imaging parameters are the heart-to-mediastinum ratio and washout rate, customarily derived from planar images. Focal tracer deficits on tomographic imaging also show prognostic utility, with some data suggesting that the best approach to tomographic image interpretation may differ from conventional methods. Cardiac ¹²³I-mIBG image findings strongly correlate with the severity and prognosis of many cardiovascular diseases, especially heart failure and ventricular arrhythmias. Cardiac ¹²³I-mIBG imaging in heart failure is FDA approved for prognostic purposes. With the robustly demonstrated ability to predict occurrence of potentially fatal arrhythmias, cardiac ¹²³I-mIBG imaging shows promise for better selecting patients who will benefit from an implantable cardioverter defibrillator, but clinical use has been hampered by lack of the randomized trial needed for incorporation into societal guidelines. In patients with ischemic heart disease, cardiac ¹²³I-mIBG imaging aids in assessing the extent of damage and in identifying arrhythmogenic regions. There have also been studies using cardiac ¹²³I-mIBG for other conditions, including patients following heart transplantation, diabetic related cardiac abnormalities and chemotherapy induced cardiotoxicity. Positron emission tomographic adrenergic radiotracers, that improve image quality, have been investigated, especially ¹¹C-meta-hydroxyephedrine, and most recently ¹⁸F-fluorbenguan. Cadmium-zinc-telluride cameras also improve image quality. With better spatial resolution and quantification, PET tracers and advanced camera technologies promise to expand the clinical utility of cardiac sympathetic imaging.

Current Status of Myocardial Perfusion Imaging With New SPECT/CT Cameras

Myocardial perfusion imaging (MPI) with Single-Photon Emission Computed Tomography (SPECT) has a major role in the management of coronary artery disease. Recent technological advances regarding SPECT detectors with the use of solid-state detectors has allowed for improved imaging quality since a decade with dramatic dose and/or time reduction of imaging protocols due to improved sensitivity and spatial resolution, and is now performed as a routine exam. Interestingly, this new technology has modified our everyday practice, from acquisition protocols (low dose and ultra-fast protocols) to image semiology. Numerous studies have shown how these technical advances have allowed for improved patient management, with similar or improved diagnostic and prognostic information derived from MPI. These improvements have also led to the straightforward implementation of myocardial blood flow measurement. This article reviews the current status of MPI using new SPECT and SPECT/CT cameras.

[123 I-MIBG scintigraphy in the assessment of heart failure prognosis and effectiveness of cardiac resynchronization therapy]

Cardiac resynchronization therapy (CRT) is one of the methods of treating patients with chronic heart failure, which can reduce the mortality rate of this group. Scintigraphic assessment of sympathetic myocardial innervation allows us to evaluate the heart failure prognosis and the effectiveness of interventional treatment. The method is based on use of the radiopharmaceutical 123 I-methiodiobenzylguanidine (123 I-MIBG), which is a structural analogue of norepinephrine and is able to selectively accumulate in the sympathetic nerve endings. This review includes a brief description of norepinephrine metabolism and pharmacokinetics of 123 I-MIBG in the sympathetic nerve ending, a brief description of the study methodology and the clinical significance of this method in patients with heart failure. Particular attention is paid to the possibilities of using this method in patients with severe chronic heart failure before and after CRT.

[Visualisation and Radiofrequency Ablation of Sympathetic Innervation Loci in the Left Atrium in Patients with Paroxysmal Atrial Fibrillation]

INTRODUCTION

A novel cardiac gamma camera utilizes the radiopharmaceutical Iodine-123-Meta-iodobenzylguanidine (123I-MIBG) to visualize cardiac sympathetic innervation. Physiological accumulation of 123I-mIBG provides an anatomical quantitative determination of the structures of the autonomic nervous system (ANS) with discrete uptake areas (DUA) of sympathetic activity located in the left atrium (LA) corresponding to the main ganglionic plexi (GP) clusters that could not previously be visualized.

AIM

to visualize the DUA of the heart in patients with paroxysmal atrial fibrillation (AF) and to assess the effect of radiofrequency ablation (RFA) on DUA in LA.

MATERIALS AND METHODS

Computed tomography (CT) of the heart and radionuclide imaging with 123I-mIBG were performed in 15 patients with paroxysmal AF. The results of the study were combined with preliminary taken CT images to create a detailed anatomical map of the sympathetic activity of the heart. The processed images were combined with the 3D reconstruction of the LA, obtained with the navigation system (CARTO 3, CARTO RMT). In DUA, high-frequency stimulation (HFS) followed by RF ablation was performed using the current recommended parameters.

RESULTS

Forty-eight DUA (median 3 [3; 3]) were identified. Average activity of DUA was 1315 [1171; 1462] cnt / sec / ml. Positive response to HFS in the DUA was obtained in 8 (53.3 %) patients. Prior to ablation, no response was received to HFS in areas of LA outside the DUA. After ablation, there was no response to HFS in the DUA sites. At repeated scans 3 DUA (median 0 [0; 0]; p&lt;0.001 compared with preoperative data) were observed. Activity of DUA significantly decreased to 819 [684; 955] cnt / sec / ml (p&lt;0.001 as compared with preoperative data). Thirteen of 13 of 15 patients (87 %) had no AF / AT / AFL recurrences for 6 month follow up.

CONCLUSION

In patients with AF, the areas of sympathetic activity in LA can be visualized by physiological localized uptake of 123I-mIBG. Radiofrequency catheter ablation can target the identified sympathetic innervation structures in AF patients precisely and effectively.

Interactions between myocardial sympathetic denervation and left ventricular mechanical dyssynchrony: A CZT analysis

BACKGROUND

A correlation between left ventricular (LV) dyssynchrony (LVD) and impaired myocardial sympathetic tone has been hypothesized. We sought to assess the interactions between regional LV sympathetic innervation, perfusion, and mechanical dyssynchrony.

METHODS

Eighty-three patients underwent evaluation of LV perfusion and sympathetic innervation on 99mTc-tetrofosmin/123I-metaiodobenzylguanidine (123I-MIBG) imaging. The summed rest score and summed 123I-MIBG score (SS-MIBG) were computed. The extent of "innervation/perfusion" mismatch was defined as the number of denervated LV segments with relatively preserved perfusion. LVD was evaluated on phase analysis and the wall with latest mechanical activation identified.

RESULTS

LVD was revealed in 36 (43%) patients. Patients with LVD had more abnormal values of SRS (21 ± 9 vs 10 ± 8, P < 0.001) and SS-MIBG (29 ± 9 vs 17 ± 11, P < 0.001) than those without LVD. The presence of LVD also clustered with a higher burden of "innervation/perfusion" mismatch (P = 0.019). On per-wall analysis, LV walls with delayed mechanical activation showed a higher burden of "innervation/perfusion" mismatch (2.3 ± 1.4 segments) than normally contracting walls (1.3 ± 1.2 segments; P < 0.001). On multivariate analysis, the extent of "innervation/perfusion" mismatch was the only predictor of delayed mechanical activation (P = 0.029).

CONCLUSIONS

Patients with LVD show an elevated burden of "innervation/perfusion" mismatch that is concentrated at the level of the most dyssynchronous walls.

High-speed scanning of planar images showing 123I-MIBG uptake using a whole-body CZT camera: a phantom and clinical study

Background

The heart-to-mediastinum ratio (HMR) obtained in myocardial sympathetic innervation imaging using ¹²³I-metaiodobenzylguanidine (MIBG) is used for heart failure or Lewy body diseases (LBD). Discovery NM/CT 670 CZT, a novel whole-body scanner, enables direct HMR measurements in planar images, in contrast to cardiac-dedicated CZT-based cameras which require specific post-processing reconstruction. We sought to investigate the clinical utility of the Discovery NM/CT 670 CZT for myocardial innervation imaging and the potential time reduction.

Results

Following preliminary phantom examinations, ¹²³I-MIBG planar imaging was performed in 36 patients with suspected or known LBD to measure HMRs with a collection time of 300 s. Images for different collection times were subsequently reframed using already acquired data, and changes in HMRs were evaluated.

The HMRs for patients with versus without clinically diagnosed LBD were 1.63 ± 0.08 versus 2.21 ± 0.08 at early phase (p < 0.001) and 1.54 ± 0.09 versus 2.08 ± 0.09 at delayed phase (p < 0.001). The difference of HMRs (300 s − other collection time) became greater as the collection time became shorter. There was good consistency in HMRs between the 300-s images (reference) and the 200-s (intra-class correlation (ICC) coefficients > 0.99), 100-s (ICC coefficients > 0.97), and 50-s (ICC coefficients > 0.89) images.

Conclusions

In planar images with a whole-body CZT-based camera, the HMRs of patients with LBD were significantly lower than those without. HMRs with the collection time of 50 s and longer showed good consistency with those of 300 s in the ICC analysis. These findings indicate a clinical utility of this novel scanner for HMR measurements and potential time reductions.

Electronic supplementary material

The online version of this article (10.1186/s13550-019-0491-z) contains supplementary material, which is available to authorized users.

First assessment of simultaneous dual isotope (123I/99mTc) cardiac SPECT on two different CZT cameras: A phantom study

BACKGROUND

We studied the impact of simultaneous dual-isotope acquisition on 123I/99mTc mismatch assessment using two CZT cameras (DNM 530c, GE Healthcare and DSPECT, Biosensors International).

METHODS

We used an anthropomorphic torso phantom (respectively filled with a solution of 123I alone, 99mTc alone, and a mixture of 123I and 99mTc) and its cardiac insert with two defects mimicking two matched and mismatched defects. Mismatch extent and reconstructed image contrast were evaluated.

RESULTS

The acquisition mode (single vs dual) significantly impacted (i) 99mTc (but not 123I) reconstructed segmental activities using both camera (P < .001), and (ii) image contrast (using 123I and DNM 530c, P < .0001; and using both 123I and 99mTc with DSPECT, P < .0001). However, the defect and mismatch size were not impacted by the type of acquisition. With both DNM 530c and DSPECT, Lin's concordance correlation coefficient and Bland-Altman analysis demonstrated an almost perfect concordance and agreement between single- and simultaneous dual-isotope segmental activity (123I and 99mTc).

CONCLUSIONS

This study found no impact of the acquisition mode (single vs dual) or the type of camera (DSPECT vs DNM 530c) on 123I and 99mTc defect size and mismatch, providing a new step toward simultaneous dual-isotope acquisition for combined innervation and perfusion assessment.

Relationships between left ventricular sympathetic innervation and diastolic dysfunction: the role of myocardial innervation/perfusion mismatch

BACKGROUND

A possible relationship between cardiac sympathetic denervation and left ventricular (LV) diastolic dysfunction has been suggested. However, an evaluation of the interactions between myocardial adrenergic tone and LV perfusion and diastolic function is lacking.

METHODS AND RESULTS

Seventy-two patients underwent 99mTc-tetrofosmin/123I-metaiodobenzylguanidine (123I-MIBG) cardiac Cadmium-Zinc-Telluride (CZT) imaging. The summed rest score (SRS) and summed 123I-MIBG score (SS-MIBG) were computed as measures of regional perfusion and innervation heterogeneities. LV segments showing an impaired innervation, despite a relatively preserved perfusion (99mTc-tetrofosmin-123I-MIBG tracers' uptake ≥25%), were individuated (innervation/perfusion mismatch). The peak filling rate (PFR) was computed as a measure of LV diastolic function. Nineteen of the 72 (26%) patients presented a normal LV diastolic function, while 29 (40%) and 24 (34%) had a mild and overt diastolic dysfunction. Subjects with diastolic dysfunction showed more abnormal SRS and SS-MIBG values (P < 0.001). In the global population, 502/1224 (41%) LV segments showed an innervation/perfusion mismatch. A modest correlation between the extent of cardiac innervation/perfusion mismatch and PFR values was evident (R = -0.27, P = 0.029). On multivariate analysis, the extent of regional innervation/perfusion mismatch remained an independent predictor of overt LV diastolic abnormalities (P = 0.017).

CONCLUSIONS

The burden of LV regions showing an innervation/perfusion mismatch associates with the occurrence of overt diastolic dysfunction.

Current Clinical Applications and Next Steps for Cardiac Innervation Imaging

PURPOSE OF REVIEW

Autonomic innervation is crucial for regulating cardiac function. Sympathetic innervation imaging with ¹²³I-mIBG and analogous PET tracers assesses disease in ways that differ from customary methods. This review describes practical use in various clinical scenarios, discusses recent guidelines, presents new data confirming risk stratification power, describes an ongoing prospective study, and looks forward to wider use in patient management.

RECENT FINDINGS

ASNC ¹²³I-mIBG guidelines are available, expanding on European guidelines. ADMIRE-HF patient follow-up increased to 2 years in ADMIRE HFX, demonstrating independent mortality risk reclassification. ADMIRE-HF findings were substantiated in a Japanese consortium study and in the PAREPET ¹¹C-HED PET study. Exciting potential uses of adrenergic imaging are management of LVADs and VT ablation. CZT cameras provide advantages, but derived parameters differ from Anger camera values. Independent risk stratification utility of adrenergic imaging with ¹²³I-mIBG and PET tracers is continuously being confirmed. An ongoing prospective randomized study promises to establish patient management utility. There is potential for wider use and improved images with newer cameras and PET.

Optimization of a simultaneous dual-isotope 201Tl/123I-MIBG myocardial SPECT imaging protocol with a CZT camera for trigger zone assessment after myocardial infarction for routine clinical settings: Are delayed acquisition and scatter correction necessary?

BACKGROUND

Dual-isotope 201Tl/123I-MIBG SPECT can assess trigger zones (dysfunctions in the autonomic nervous system located in areas of viable myocardium) that are substrate for ventricular arrhythmias after STEMI. This study evaluated the necessity of delayed acquisition and scatter correction for dual-isotope 201Tl/123I-MIBG SPECT studies with a CZT camera to identify trigger zones after revascularization in patients with STEMI in routine clinical settings.

METHODS

Sixty-nine patients were prospectively enrolled after revascularization to undergo 201Tl/123I-MIBG SPECT using a CZT camera (Discovery NM 530c, GE). The first acquisition was a single thallium study (before MIBG administration); the second and the third were early and late dual-isotope studies. We compared the scatter-uncorrected and scatter-corrected (TEW method) thallium studies with the results of magnetic resonance imaging or transthoracic echography (reference standard) to diagnose myocardial necrosis.

RESULTS

Summed rest scores (SRS) were significantly higher in the delayed MIBG studies than the early MIBG studies. SRS and necrosis surface were significantly higher in the delayed thallium studies with scatter correction than without scatter correction, leading to less trigger zone diagnosis for the scatter-corrected studies. Compared with the scatter-uncorrected studies, the late thallium scatter-corrected studies provided the best diagnostic values for myocardial necrosis assessment.

CONCLUSIONS

Delayed acquisitions and scatter-corrected dual-isotope 201Tl/123I-MIBG SPECT acquisitions provide an improved evaluation of trigger zones in routine clinical settings after revascularization for STEMI.

Determination of the Heart-to-Mediastinum Ratio of 123I-MIBG Uptake Using Dual-Isotope (123I-MIBG/99mTc-Tetrofosmin) Multipinhole Cadmium-Zinc-Telluride SPECT in Patients with Heart Failure

The aim of this retrospective study was to compare the heart-to-mediastinum ratio (HMR) of ¹²³I-metaiodobenzylguanidine (¹²³I-MIBG) uptake obtained using a multipinhole cadmium-zinc-telluride (CZT) camera with that obtained using conventional planar imaging. Methods: Forty consecutive heart failure patients underwent planar acquisition 4 h after ¹²³I-MIBG injection (191 ± 41 [mean ± SD] MBq). To localize the heart using the CZT camera, ^99mTc-tetrofosmin (358 ± 177 MBq) was administered and dual-isotope acquisition was performed. The HMRs were calculated with conventional planar imaging (HMR_planar), with anterior reprojection images using the CZT camera (HMR_reproj), and with transaxial reconstructed images using the CZT camera (HMR_transaxial). In a phantom study, we estimated a linear model fitting the CZT camera data to the planar data, and we applied it to provide corrected CZT camera-determined HMRs in patients (cHMR_reproj and cHMR_transaxial). Results: Thirty-four men and 6 women (71 ± 9 y old) with ischemic (22 patients) and nonischemic (18 patients) heart failure completed the study. For 22 of the 40 patients (55%), the New York Heart Association classification was class II and the ejection fraction was 35% ± 9%. HMR_reproj (1.12 ± 0.19) and HMR_transaxial (1.35 ± 0.34) were lower than HMR_planar (1.44 ± 0.14) (P < 0.0001 and P < 0.01, respectively). cHMR_reproj (1.54 ± 0.09) and cHMR_transaxial (1.45 ± 0.14) were significantly different (P < 0.0001). Lin concordance correlation and Bland-Altman analysis demonstrated an almost perfect concordance and a high agreement between HMR_planar and cHMR_transaxial (P was not significant) but not between HMR_planar and cHMR_reproj (P < 0.0001). Conclusion: This study demonstrated that determination of the late HMR of cardiac ¹²³I-MIBG uptake using dual-isotope (¹²³I and ^99mTc) acquisition on a multipinhole CZT camera was feasible in patients with heart failure. However, this determination should be performed using transaxial reconstructed images and linear correction based on phantom data acquisitions.

Left ventricular function assessment using 123I/99mTc dual-isotope acquisition with two semi-conductor cadmium-zinc-telluride (CZT) cameras: a gated cardiac phantom study

BACKGROUND

The impact of increased energy resolution of cadmium-zinc-telluride (CZT) cameras on the assessment of left ventricular function under dual-isotope conditions (^99mTc and ¹²³I) remains unknown. The Amsterdam-gated dynamic cardiac phantom (AGATE, Vanderwilt techniques, Boxtel, The Netherlands) was successively filled with a solution of ¹²³I alone, ^99mTc alone, and a mixture of ¹²³I and ^99mTc. A total of 12 datasets was acquired with each commercially available CZT camera (DNM 530c, GE Healthcare and DSPECT, Biosensors International) using both energy windows (^99mTc or ¹²³I) with ejection fraction set to 33, 45, and 60 %. End-diastolic (EDV) and end-systolic (ESV) volumes, ejection fraction (LVEF), and regional wall motion and thickening (17-segment model) were assessed using Cedars-Sinai QGS Software. Concordance between single- and dual-isotope acquisitions was tested using Lin's concordance correlation coefficient (CCC) and Bland-Altman plots.

RESULTS

There was no significant difference between single- or simultaneous dual-isotope acquisition (¹²³I and ^99mTc) for EDV, ESV, LVEF, or segmental wall motion and thickening. Myocardial volumes using single- (¹²³I, ^99mTc) and dual-isotope (reconstructed using both ¹²³I and ^99mTc energy windows) acquisitions were, respectively, the following: EDV (mL) 88 ± 27 vs. 89 ± 27 vs. 92 ± 29 vs. 90 ± 26 for DNM 530c (p = NS) and 82 ± 20 vs. 83 ± 22 vs. 79 ± 19 vs. 77 ± 20 for DSPECT (p = NS); ESV (mL) 40 ± 1 vs. 41 ± 2 vs. 41 ± 2 vs. 42 ± 1 for DNM 530c (p = NS) and 37 ± 5 vs. 37 ± 1 vs. 35 ± 3 vs. 34 ± 2 for DSPECT (p = NS); LVEF (%) 52 ± 14 vs. 51 ± 13 vs. 53 ± 13 vs. 51 ± 13 for DNM 530c (p = NS) and 52 ± 16 vs. 54 ± 13 vs. 54 ± 14 vs. 54 ± 13 for DSPECT (p = NS); regional motion (mm) 6.72 ± 2.82 vs. 6.58 ± 2.52 vs. 6.86 ± 2.99 vs. 6.59 ± 2.76 for DNM 530c (p = NS) and 6.79 ± 3.17 vs. 6.81 ± 2.75 vs. 6.71 ± 2.50 vs. 6.62 ± 2.74 for DSPECT (p = NS). The type of camera significantly impacted only on ESV (p < 0.001).

CONCLUSIONS

The new CZT cameras yielded similar results for the assessment of LVEF and regional motion using different energy windows (¹²³I or ^99mTc) and acquisition types (single vs. dual). With simultaneous dual-isotope acquisitions, the presence of ¹²³I did not impact on LVEF assessment within the ^99mTc energy window for either CZT camera.

Performance of cardiac cadmium-zinc-telluride gamma camera imaging in coronary artery disease: a review from the cardiovascular committee of the European Association of Nuclear Medicine (EANM)

The trade-off between resolution and count sensitivity dominates the performance of standard gamma cameras and dictates the need for relatively high doses of radioactivity of the used radiopharmaceuticals in order to limit image acquisition duration. The introduction of cadmium-zinc-telluride (CZT)-based cameras may overcome some of the limitations against conventional gamma cameras. CZT cameras used for the evaluation of myocardial perfusion have been shown to have a higher count sensitivity compared to conventional single photon emission computed tomography (SPECT) techniques. CZT image quality is further improved by the development of a dedicated three-dimensional iterative reconstruction algorithm, based on maximum likelihood expectation maximization (MLEM), which corrects for the loss in spatial resolution due to line response function of the collimator. All these innovations significantly reduce imaging time and result in a lower patient's radiation exposure compared with standard SPECT. To guide current and possible future users of the CZT technique for myocardial perfusion imaging, the Cardiovascular Committee of the European Association of Nuclear Medicine, starting from the experience of its members, has decided to examine the current literature regarding procedures and clinical data on CZT cameras. The committee hereby aims 1) to identify the main acquisitions protocols; 2) to evaluate the diagnostic and prognostic value of CZT derived myocardial perfusion, and finally 3) to determine the impact of CZT on radiation exposure.

123I-MIBG SPECT for Evaluation of Patients with Heart Failure

Heart failure (HF) is characterized by activation of the sympathetic cardiac nerves. The condition of cardiac sympathetic nerves can be evaluated by (123)I-metaiodobenzylguanidine ((123)I-MIBG) imaging. Most cardiac (123)I-MIBG studies have relied on measurements from anterior planar images of the chest. However, it has become progressively more common to include SPECT imaging in clinical and research protocols. This review examines recent trends in (123)I-MIBG SPECT imaging and evidence that provides the basis for the increased use of the procedure in the clinical management of patients with HF. (123)I-MIBG SPECT has been shown to be complementary to planar imaging in patients with HF in studies of coronary artery disease after an acute myocardial infarction. Moreover, (123)I-MIBG SPECT has been used in numerous studies to document regional denervation for arrhythmic event risk assessment. For better quantification of the size and severity of innervation abnormalities in (123)I-MIBG SPECT, programs and protocols specifically for (123)I have been developed. Also, the introduction of new solid-state cameras has created the potential for more rapid SPECT acquisitions or a reduction in radiopharmaceutical activity. Although PET imaging has superior quantitative capabilities, (123)I-MIBG SPECT is, for the foreseeable future, the only widely available nuclear imaging method for assessing regional myocardial sympathetic innervation.

Clinical Applications of Myocardial Innervation Imaging

Cardiac autonomic innervation plays an important role in regulating function. Adrenergic innervation imaging is possible with the norepinephrine analogue radiotracer iodine 123 meta-iodobenzylguanidine ((123)I-mIBG) and positron emitting tracers such carbon-11 hydroxyephedrine. (123)I-mIBG uptake is assessed globally via the heart to mediastinum ratio on planar images and regionally with tomographic imaging and has utility in various cardiac diseases. There is promise for guiding expensive invasive therapies such as implantable defibrillators, ventricular assist devices, and transplant. There are reports of utility in primary arrhythmic conditions, ischemic heart disease, and diabetes and after cardiac damaging chemotherapy.

First determination of the heart-to-mediastinum ratio using cardiac dual isotope (¹²³I-MIBG/⁹⁹mTc-tetrofosmin) CZT imaging in patients with heart failure: the ADRECARD study

PURPOSE

Cardiac innervation is assessed using the heart-to-mediastinum ratio (HMR) of metaiodobenzylguanidine (MIBG) on planar imaging using Anger single photon emission computed tomography (A-SPECT). The aim of the study was to determine the HMR of MIBG obtained using a CZT-based camera (D-SPECT; Spectrum Dynamics, Israel) in comparison with that obtained using conventional planar imaging.

METHODS

The ADRECARD study prospectively evaluated 44 patients with heart failure. They underwent planar acquisition using the A-SPECT camera 4 h after (123)I-MIBG injection (236.4 ± 39.7 MBq). To localize the heart using D-SPECT, (99m)Tc-tetrofosmin (753 ± 133 MBq) was administered and dual isotope acquisition was performed using the D-SPECT system. HMR was calculated using both planar A-SPECT imaging and front view D-SPECT cine data. In a phantom study, we estimated a model fitting the A-SPECT and the D-SPECT data that was further applied to correct for differences between the cameras.

RESULTS

A total of 44 patients (39 men and 5 women, aged 60 ± 11 years) with ischaemic (31 patients) and nonischaemic (13 patients) cardiomyopathy completed the study. Most patients (28 of 44) were NYHA class II, and the mean left ventricular ejection fraction was 33 ± 7 %. The mean HMR values were 1.34 ± 0.15 and 1.45 ± 0.27 from A-SPECT and D-SPECT, respectively (p < 0.0001). After correction, Lin's concordance correlation showed an almost perfect concordance between corrected D-SPECT HMR and A-SPECT HMR, and Bland-Altman analysis demonstrated a high agreement between the two measurements.

CONCLUSION

The ADRECARD study demonstrated that determination of late HMR during cardiac MIBG imaging using dual isotope ((123)I and (99m)Tc) acquisition on a CZT camera (D-SPECT) is feasible in patients with heart failure. A linear correction based on the phantom study yielded a high agreement between (123)I MIBG HMR obtained using a CZT camera and that from conventional planar imaging.

Regional heterogeneity in cardiac sympathetic innervation in acute myocardial infarction: relationship with myocardial oedema on magnetic resonance

PURPOSE

To assess the relationships between myocardial structure and function on cardiac magnetic resonance (CMR) imaging and sympathetic tone on (123)I-metaiodobenzylguanidine ((123)I-MIBG) scintigraphy early after myocardial infarction (MI).

METHODS

Ten patients underwent (123)I-MIBG and (99m)Tc-tetrofosmin rest cadmium zinc telluride scintigraphy 4 ± 1 days after MI. The segmental left ventricular (LV) relative radiotracer uptake of both (99m)Tc-tetrofosmin and early (123)I-MIBG was calculated. The day after scintigraphy, on CMR imaging, the extent of ischaemia-related oedema and of myocardial fibrosis (late gadolinium enhancement, LGE) was assessed. Accordingly, the extent of oedema and LGE was evaluated for each segment and segmental wall thickening determined. Based on LGE distribution, LV segments were categorized as "infarcted" (56 segments), "adjacent" (66 segments) or "remote" (48 segments).

RESULTS

Infarcted segments showed a more depressed systolic wall thickening and greater extent of oedema than adjacent segments (p < 0.001) and remote segments (p < 0.001). Interestingly, while uptake of (99m)Tc-tetrofosmin was significantly depressed only in infarcted segments (p < 0.001 vs. both adjacent and remote segments), uptake of (123)I-MIBG was impaired not only in infarcted segments (p < 0.001 vs. remote) but also in adjacent segments (p = 0.024 vs. remote segments). At the regional level, after correction for (99m)Tc-tetrofosmin and LGE distribution, segmental (123)I-MIBG uptake (p < 0.001) remained an independent predictor of ischaemia-related oedema.

CONCLUSION

After acute MI the regional impairment of sympathetic tone extends beyond the area of altered myocardial perfusion and is associated with myocardial oedema.