Nuclear Cardiology: Present and Future

Advanced Cardiac Imaging and Women's Chest Pain: A Question of Gender

Awareness of gender differences in cardiovascular disease (CVD) has increased: both the different impact of traditional cardiovascular risk factors on women and the existence of sex-specific risk factors have been demonstrated. Therefore, it is essential to recognize typical aspects of ischemic heart disease (IHD) in women, who usually show a lower prevalence of obstructive coronary artery disease (CAD) as a cause of acute coronary syndrome (ACS). It is also important to know how to recognize pathologies that can cause acute chest pain with a higher incidence in women, such as spontaneous coronary artery dissection (SCAD) and myocardial infarction with non-obstructive coronary arteries (MINOCA). Coronary computed tomography angiography (CCTA) and cardiac magnetic resonance imaging (CMR) gained a pivotal role in the context of cardiac emergencies. Thus, the aim of our review is to investigate the most frequent scenarios in women with acute chest pain and how advanced cardiac imaging can help in the management and diagnosis of ACS.

One-pot synthesis and biodistribution of fluorine-18 labeled serum albumin for vascular imaging

INTRODUCTION

Equilibrium single-photon radionuclide imaging methods for assessing cardiac function and the integrity of the vascular system have long been in use for both clinical and research purposes. However, positron-emitting blood pool agents that could provide PET equivalents to these (and other) clinical procedures have not yet been adopted despite technical imaging advantages offered by PET. Our goal was to develop a PET blood pool tracer that not only meets necessary in vivo biological requirements but can be produced with an uncomplicated and rapid synthesis method which would facilitate clinical translation. Herein, albumin labeled with fluorine-18 was synthesized using a one-pot method and evaluated in vitro and in vivo in rats.

METHODS

A ligand (NODA-Bz-TFPE), containing NODA attached to a tetrafluorophenylester (TFPE) via a phenyl linker (Bz), was labeled with aluminum fluoride (Al[18F]F). Conjugation of the serum albumin with the ligand (Al[18F]F-NODA-Bz-TFPE), followed by purification (size exclusion chromatography), yielded the final product (Al[18F]F-NODA-Bz-RSA/HSA). In vitro stability was evaluated in human serum albumin by HPLC. Rat biodistributions and whole-body PET imaging over a 4 h time course were used for the in vivo evaluation.

RESULTS

This synthesis exhibited an overall radiochemical yield of 45 ± 10% (n = 30), a 50-min radiolabeling time, a radiochemical purity >99% and apparent stability up to 4 h in human serum. Blood had the highest retention of Al[18F]F-NODA-Bz-RSA at all times with a blood half-life of 5.2 h in rats. Al[18F]F-NODA-Bz-RSA distribution in most rat tissues remained relatively constant for up to 1 h, indicating that the tissue radioactivity content represents the respective tissue plasma volume. Dynamic whole-body PET images were in agreement with these findings.

CONCLUSIONS

A new ligand has been developed and radiolabeled with Al[18F]F that allows rapid (50-min) preparation of fluorine-18 serum albumin in one-pot. In addition to increased synthetic efficiency, the construct appears to be metabolically stable in rats. This method could encourage wider use of PET to quantify cardiac function and tissue vascular integrity in both research and clinical settings.

Microcalcifications, Their Genesis, Growth, and Biomechanical Stability in Fibrous Cap Rupture

For many decades, cardiovascular calcification has been considered as a passive process, accompanying atheroma progression, correlated with plaque burden, and apparently without a major role on plaque vulnerability. Clinical and pathological analyses have previously focused on the total amount of calcification (calcified area in a whole atheroma cross section) and whether more calcification means higher risk of plaque rupture or not. However, this paradigm has been changing in the last decade or so. Recent research has focused on the presence of microcalcifications (μCalcs) in the atheroma and more importantly on whether clusters of μCalcs are located in the cap of the atheroma. While the vast majority of μCalcs are found in the lipid pool or necrotic core, they are inconsequential to vulnerable plaque. Nevertheless, it has been shown that μCalcs located within the fibrous cap could be numerous and that they behave as an intensifier of the background circumferential stress in the cap. It is now known that such intensifying effect depends on the size and shape of the μCalc as well as the proximity between two or more μCalcs. If μCalcs are located in caps with very low background stress, the increase in stress concentration may not be sufficient to reach the rupture threshold. However, the presence of μCalc(s) in the cap with a background stress of about one fifth to one half the rupture threshold (a stable plaque) will produce a significant increase in local stress, which may exceed the cap rupture threshold and thus transform a non-vulnerable plaque into a vulnerable one. Also, the classic view that treats cardiovascular calcification as a passive process has been challenged, and emerging data suggest that cardiovascular calcification may encompass both passive and active processes. The passive calcification process comprises biochemical factors, specifically circulating nucleating complexes, which would lead to calcification of the atheroma. The active mechanism of atherosclerotic calcification is a cell-mediated process via cell death of macrophages and smooth muscle cells (SMCs) and/or the release of matrix vesicles by SMCs.

Correlation between Transient Ischemic Dilation Index and Endothelin-1 Level in Patients with Type 2 Diabetes Mellitus

Transient ischemic dilation (TID) is a sensitive and specific marker for detecting the severity and extent of coronary artery disease (CAD), which is closely associated with endothelial dysfunction. TID can be observed on stress-rest myocardial perfusion scan (MPS) due to subendocardial hypoperfusion. Hyperglycemia in type 2 diabetes mellitus (T2DM) could lead to micro- and macrovascular complications and begins with endothelial dysfunction. Endothelin-1 (ET-1), a potent vasocontrictor, increases in endothelial dysfunction. The aim of this study was to examine the correlation between TID index and ET​​-1 levels in T2DM patients without any sign or symptom of cardiovascular complication. An analytic-correlational cross-sectional study was done on T2DM patients who met the inclusion criteria and agreed to participate by signing an informed consent form. The TID index was calculated automatically using standard software provided by the gamma camera GE-Infinia. Stress-rest MPS was done using technetium-99m ((99m)Tc)-tetrofosmin and a pharmacological stress test using adenosine. The ET-1 level was determined by radioimmunoassay. Data distribution was analyzed using the Shapiro-Wilk normality test. The Mann-Whitney test was used to compare the average difference of the variables and Spearman's rank for correlation analysis. A total of 47 subjects consisting of 24 (51%) males and 23 (49%) females were included in this study. The age range was 37-74 years (54.3 ± 8.4). The TID index range was 0.86-1.26 (median = 1.12) and abnormal TID index was found in 23/47 (49%) subjects. ET-1 levels range 8.02-17.91 pg/mL (median = 11.08). The results showed no significant differences in age, ET-1 levels, and TID index based on age and sex (P > 0.05). There was a significant positive correlation between TID index and ET-1 level with r = 0.7 and P < 0.001. There was a positive correlation between TID index and ET-1 plasma level in patients with T2DM.

Influence of the arm position in myocardial perfusion imaging acquisition

OBJECTIVE

despite the technologic advances in myocardial perfusion imaging, we keep using an uncomfortable and sometimes impracticable patient position - supine with arms raised above the head (U). The purpose of this study was to investigate whether perfusion and functional cardiac gated SPECT scan results of acquisition U are equivalent to another position modality: supine with arms down at the sides of the trunk (D).

METHODS AND RESULTS

we performed U acquisition and in sequence D acquisition in 120 patients (pts) using a one-day MPI (rest-gated/stress), with 99mTc-sestamibi (370 MBq and 1110 MBq). Images were processed by the iterative reconstruction method (OSEM). Rest (R) and stress (S) studies were scored using 17-segments model. Functional parameters (left ventricular ejection fraction, and volumes) were automatically obtained by the quantitative gated SPECT (QGS) program. According to the degree of stress defects observed in U study, the patients were categorized in two subgroups: normal (SSS ≤ 3 or < 5%) and abnormal (SSS>3 or ≥ 5%). Shoulder/back pain occurred in 23.3% of U patients and in 5% of D. No significant differences between U and D were found for SSS (p = 0.82) and SRS (p = 0.74) in normal group. In abnormal group, good correlation was found between U and D modes for SSS (Rho = 0.95, p = 0.0001) and SRS (Rho = 0.96 p = 0.0001), but the mean SSS (12.53 ± 7.54) and SRS (10.60 ± 7.08) values of D were significantly lower (p < 0.05) than SSS (13.43 ± 6.81) and SRS (11.33 ± 6.97) of U mode. Function measurements presented good correlations, except for end-diastolic volume (p = 0.0001).

CONCLUSION

although D mode appears to be more comfortable and presented a good correlation with U values of SSS and SRS, in abnormal pts, the extent and severity of defects can be underestimated. Considering clinical implications of an accurate perfusion measurement, the acquisition with the arms down should be avoided.

Characterization of the four isomers of (123)I-CMICE-013: a potential SPECT myocardial perfusion imaging agent

Myocardial perfusion imaging (MPI) with single photon emission computed tomography (SPECT) is widely used in the assessment of coronary artery disease (CAD). We have developed (123)I-CMICE-013 based on rotenone, a mitochondrial complex I (MC-1) inhibitor, as a promising new MPI agent. Our synthesis results in a mixture of four species of (123)I-CMICE-013 A, B, C, D. In this study, we separated the four species and evaluated their biodistribution and imaging properties. The cold analogs (127)I-CMICE-013 A, B, C, D were isolated and characterized and their chemical structures proposed.

METHODS

(123)I-CMICE-013 was synthesized by radiolabeling rotenone with Na(123)I in trifluoroacetic acid (TFA) with iodogen as the oxidizing agent at 60°C for 45min, and the four species were separated by RP-HPLC. The cold analogs (127)I-CMICE-013 A, B, C and D were isolated with a similar procedure and characterized by NMR and mass spectrometry. Biodistribution and microSPECT imaging studies were carried out on normal rats.

RESULTS

We propose the mechanism of the rotenone iodination and the structures of the four species. First, I(+) forms an intermediate three-membered ring with 6' and 7' carbons. Second, the lone electron pair of the water molecule attacks the 6' or 7'-carbon, following by the formation of 6'-OH, and 7'-I bonds as in major products C and D, or 6'-I and 7'-OH bonds as in minor products A and B. The weaker 6'-I bond in the intermediate prompts the nucleophilic attachment of water at the favorable 6'-carbon to generate C and D. MicroSPECT images of (123)I-CMICE-013 A, B, C, D in rats showed clear visualization of myocardium and little interference from lung and liver. The imaging time activity curves and biodistribution data showed complex profiles for the four isomers, which is not expected from the structure activity relationship theory.

CONCLUSION

(123/127)I-CMICE-013 A and B are constitutional isomers with C and D, while A and C are diastereomers of B and D, respectively. Overall, the biological characteristics of the four species are not correlated perfectly with their molecular structures.

Pharmacokinetics and biodistribution of 99mTc N-MPO in healthy human volunteers

PURPOSE

Tc N-MPO ([Tc N(MPO)(PNP5)]: HMPO = 2-mercaptopyridine N-oxide, and PNP5 = N-ethoxyethyl-N,N-bis[2-(bis(3-methoxypropyl)phosphino)ethyl]amine) is a new Tc radiotracer useful for myocardial perfusion imaging. This study was designed to determine its pharmacokinetics and biodistribution in healthy volunteers.

PATIENTS AND METHODS

Ten healthy volunteers were involved in this study. Each subject was administered approximately 925 MBq of Tc N-MPO under rest or stress conditions (n = 5 per group). Whole-body planar images were obtained at 10, 30, 60, 240, and 1440 minutes after injection. Organ uptake was quantified by region-of-interest analysis. The blood clearance and urine excretion kinetics were determined by collecting blood and urine samples at different time points.

RESULTS

Tc N-MPO showed significant accumulation in myocardium with prolonged retention. At rest, its percentage of injected dose (%ID) uptake in the heart, lungs, and liver at 10 minutes after injection was 2.47% (0.64%), 1.84% (0.64%), and 20.88% (5.23%), respectively. The liver uptake decreased to 6.79%ID (1.60%ID) at 60 minutes after injection and 4.50%ID (1.86%ID) at 240 minutes after injection. Under stress conditions, the heart uptake was slightly increased (2.57%ID [0.21%ID]). The rapid liver clearance led to favorable heart-to-liver ratios, reaching values of 0.27%ID (0.07%ID) under rest condition and 0.28%ID (0.05%ID) under stress condition at 60 minutes after injection.

CONCLUSIONS

Tc N-MPO demonstrates a highly favorable biodistribution in humans. The high heart uptake and the fast liver washout of Tc N-MPO will allow SPECT images of the left ventricle to be acquired as early as 10 minutes after injection.

Changing views of the biomechanics of vulnerable plaque rupture: a review

This review examines changing perspectives on the biomechanics of vulnerable plaque rupture over the past 25 years from the first finite element analyses (FEA) showing that the presence of a lipid pool significantly increases the local tissue stress in the atheroma cap to the latest imaging and 3D FEA studies revealing numerous microcalcifications in the cap proper and a new paradigm for cap rupture. The first part of the review summarizes studies describing the role of the fibrous cap thickness, tissue properties, and lesion geometry as main determinants of the risk of rupture. Advantages and limitations of current imaging technologies for assessment of vulnerable plaques are also discussed. However, the basic paradoxes as to why ruptures frequently did not coincide with location of PCS and why caps >65 μm thickness could rupture at tissue stresses significantly below the 300 kPa critical threshold still remained unresolved. The second part of the review describes recent studies in the role of microcalcifications, their origin, shape, and clustering in explaining these unresolved issues including the actual mechanism of rupture due to the explosive growth of tiny voids (cavitation) in local regions of high stress concentration between closely spaced microinclusions oriented along their tensile axis.

Comparison of ⁹⁹mTc-N-DBODC5 and ⁹⁹mTc-MIBI of myocardial perfusion imaging for diagnosis of coronary artery disease

Despite recent advances in therapeutic and diagnostic approaches, coronary artery disease (CAD) and its related cardiac disorders represent the most common cause of death in the United States. Nuclear myocardial perfusion imaging (MPI) technologies play a pivotal role in the diagnosis and treatment design for CAD. Recently, in order to develop improved MPI agents for diagnosis of CAD, (99m)Tc-[bis(dimethoxypropylphosphinoethyl)-ethoxyethyl-amine(PNP5)]-[bis(N-ethoxyethyl)dithiocarbamato(DBODC)]nitride(N-DBODC5)((99m)Tc-N-DBODC5) with a faster liver clearance than conventional single-photon emission computed tomography (SPECT) imaging agents (technetium 99m sestamibi ((99m)Tc-MIBI) or technetium 99m tetrofosmin) has been introduced. In preclinical and phase I studies, (99m)Tc-N-DBODC5 has shown characteristics of an essentially ideal MPI tracer. Importantly, however, there is no data to support the use of (99m)Tc-N-DBODC5 to evaluate myocardial ischemia in patients with suspected CAD. The present study was designed to assess the clinical value of this agent; the findings of stress and rest MPI after the administration of this agent were compared to those of stress and rest (99m)Tc-MIBI, as well as those of coronary angiography, with respect to the detection of CAD. Our findings indicated the usefulness of (99m)Tc-N-DBODC5 as a promising MPI agent.

Radiation doses to Norwegian heart-transplanted patients undergoing annual coronary angiography

Heart-transplanted patients in Norway undergo annual coronary angiography (CA). The aims of this study were to establish a conversion factor between dose-area product and effective dose for these examinations and to use this to evaluate the accumulated radiation dose and risks associated with annual CA. An experienced cardiac interventionist performed a simulated examination on an Alderson phantom loaded with thermoluminescence dosemeters. The simulated CA examination yielded a dose-area product of 17 Gy cm(2) and an effective dose of 3.4 mSv: the conversion factor between dose-area product and effective dose was 0.20 mSv Gy cm(-2). Dose-area product values from 200 heart-transplanted patients that had undergone 906 CA examinations between 2001 and 2008 were retrieved from the institutional database. Mean dose-area product from annual CA was 25 Gy cm(2), ranging from 2 to 140 Gy cm(2). Mean number of CA procedure was 8 (range, 1-23). Mean accumulated effective dose for Norwegian heart-transplanted patients between 2001 and 2008 was 34 mSv (range, 5-113 mSv). Doses and radiation risks for heart-transplanted patients are generally low, because most heart transplantations are performed on middle-aged patients with limited life expectancy. Special concern should however be taken to reduce doses for young heart-transplanted patients who are committed to lifelong follow-up of their transplanted heart.

Advances in PET myocardial perfusion imaging: F-18 labeled tracers

Coronary artery disease and its related cardiac disorders represent the most common cause of death in the USA and Western world. Despite advancements in treatment and accompanying improvements in outcome with current diagnostic and therapeutic modalities, it is the correct assignment of these diagnostic techniques and treatment options which are crucial. From a diagnostic standpoint, SPECT myocardial perfusion imaging (MPI) using traditional radiotracers like thallium-201 chloride, Tc-99m sestamibi or Tc-99m tetrofosmin is the most utilized imaging technique. However, PET MPI using N-13 ammonia, rubidium-82 chloride or O-15 water is increasing in availability and usage as a result of the growing number of medical centers with new-generation PET/CT systems taking advantage of the superior imaging properties of PET over SPECT. The routine clinical use of PET MPI is still limited, in part because of the short half-life of conventional PET MPI tracers. The disadvantages of these conventional PET tracers include expensive onsite production and inconvenient on-scanner tracer administration making them unsuitable for physical exercise stress imaging. Recently, two F-18 labeled radiotracers with longer radioactive half-lives than conventional PET imaging agents have been introduced. These are flurpiridaz F 18 (formerly known as F-18 BMS747158-02) and F-18 fluorobenzyltriphenylphosphonium. These longer half-life F-18 labeled perfusion tracers can overcome the production and protocol limitations of currently used radiotracers for PET MPI.

Myocardial perfusion scintigraphy: techniques, interpretation, indications and reporting

Myocardial perfusion single photon emission-computed tomography (MPS) has been one of the most important and common non-invasive diagnostic cardiac test. Gated MPS provides simultaneous assessment of myocardial perfusion and function with only one study. With appropriate attention to the MPS techniques, appropriate clinical utilization and effective reporting, gated MPS will remain a useful diagnostic test for many years to come. The aim of this article is to review the basic techniques of MPS, a simplified systematic approach for study interpretation, current clinical indications and reporting. After reading this article the reader should develop an understanding of the techniques, interpretation, current clinical indications and reporting of MPS studies.

Sequence variations in the FII, FV, F13A1, FGB and PAI-1 genes are associated with differences in myocardial perfusion

AIMS

Coronary artery disease (CAD) is a significant cause of morbidity and mortality in modern societies. The association between genetic markers and CAD is still poorly understood. In this study, we evaluated the effect of five genetic variants: Factor V Leiden (FV:c.1691G>A) (rs6025), Factor II prothrombin (FII:c.20210G>A; rs1799963), plasminogen activator inhibitor 1 (PAI-1) -675(4G/5G; SERPINE1:g.4329_4330insG; rs34857375), β-fibrinogen -455G>A (FGB:c.4577G>A; rs1800790) and Factor XIII (F13A1:c.103G>T; rs5985) on myocardial perfusion.

MATERIALS & METHODS

We examined 523 patients using exercise-rest myocardial perfusion single photon emission computed tomography, where the summed stress score (SSS), summed rest score and summed difference score (SDS) indexes, were calculated. In order to examine the independent prognostic ability of genotype on SSS and SDS, multiple linear regression models were used.

RESULTS

It was found that Factor V Leiden, Factor XIII, β-fibrinogen and PAI-1 genotypes were independent prognostic predictors of SSS and SDS with Factor XIII exhibiting the strongest association. Moreover, Factor II prothrombin proved an independent prognostic predictor of SSS.

CONCLUSION

Our study provides the first evidence of an association between these polymorphisms and myocardial perfusion, suggesting that the process of coronary artery disease and also patients' prognosis, may be modified by the FV:c.1691G>A, FII:c.20210G>A, PAI-1 -675 (4G/5G), β-fibrinogen FGB:c.4577G>A and F13A1:c.103G>T genotypes.

A fast cardiac gamma camera with dynamic SPECT capabilities: design, system validation and future potential

PURPOSE

The goal of this study is to present the Discovery NM 530c (DNM), a cardiac SPECT camera, interfacing multi-pinhole collimators with solid-state modules, aiming at slashing acquisition time without jeopardizing quality. DNM resembles PET since it enables 3-D SPECT without detector motion. We further envision how these novel capabilities may help with current and future challenges of cardiac imaging.

METHODS

DNM sensitivity, spatial resolution (SR) and energy resolution (ER), count rate response, cardiac uniformity and cardiac defect contrast were measured and compared to a dedicated cardiac, dual-head standard SPECT (S-SPECT) camera.

RESULTS

DNM sensitivity was more than threefold higher while SR was notably better. Significantly, SR was the same for (99m)Tc and (201)Tl. ER was improved on DNM and allowed good separation of (99m)Tc and (123)I spectral peaks. Count rate remained linear on DNM up to 612 kcps, while S-SPECT showed severe dead time limitations. Phantom studies revealed comparable uniformity and defect contrast, notwithstanding significantly shorter acquisition time for the DNM. First patient images, including dynamic SPECT, are also presented.

CONCLUSION

DNM is raising the bar for expedition and upgrade of practice. It features high sensitivity as well as improved SR, temporal resolution and ER. It enables reduction of acquisition time and fast protocols. Importantly, it is potentially capable of dynamic 3-D acquisition. The new technology is potentially upgradeable and may become a milestone in the evolution of nuclear cardiology as it assumes its key role in molecular imaging of the heart.

Preparation and biodistribution of [18F]FP2OP as myocardial perfusion imaging agent for positron emission tomography

Myocardial extractions of pyridaben, a mitochondrial complex I (MC-I) inhibitor, is well correlated with blood flow. Based on the synthesis and characterization of pyridaben analogue 2-tert-butyl-5-[2-(2-[(18)F]fluroethoxy)ethoxy]benzyloxy]-4-chloro-2H-pyridazin-3-one ([(18)F]FP2OP), this study assessed its potential to be developed as myocardial perfusion imaging (MPI) agent.

METHODS

The tosylate labeling precursor 2-(2-(4-(tert-butyl-5-chloro-6-oxo-1,6-dihydro-pyridazin-4-yloxymethyl)benzyloxy)ethoxy)ethyl ester (OTs-P2OP) and the nonradioactive 2-tert-butyl-5-[2-(2-[(19)F]fluroethoxy)ethoxy]benzyloxy]-4-chloro-2H-pyridazin-3-one ([(19)F]FP2OP) were synthesized and characterized by IR, (1)H NMR, (13)C NMR and MS analysis. By substituting tosyl of precursor OTs-P2OP with (18)F, the radiolabeled complex [(18)F]FP2OP was prepared and further evaluated for its in vitro physicochemical properties, in vivo biodistribution, the metabolic stability in mice, ex vivo autoradiography and cardiac PET/CT imaging.

RESULTS

Starting with [(18)F]F(-) Kryptofix 2.2.2./K(2)CO(3) solution, the total reaction time for [(18)F]FP2OP was about 100 min, with final high-performance liquid chromatography purification included. Typical decay-corrected radiochemical yield stayed at 41+/-5.3%, the radiochemical purity, 98% or more. Biodistribution in mice showed that the heart uptake of [(18)F]FP2OP was 41.90+/-4.52%ID/g at 2 min post-injection time, when the ratio of heart/liver, heart/lung and heart/blood reached 6.83, 9.49 and 35.74, respectively. Lipophilic molecule was further produced by metabolized [(18)F]FP2OP in blood and urine at 30 min. Ex vivo autoradiography demonstrates that [(18)F]FP2OP may have high affinity with MC-I and that can be blocked by [(19)F]FP2OP or rotenone (a known MC-I inhibitor). Cardiac PET images were obtained in a Chinese mini-swine at 5, 15, 30 and 60 min post-injection time with high quality.

CONCLUSION

[(18)F]FP2OP was synthesized with high radiochemical yield. The promising biological properties of [(18)F]FP2OP suggest high potential as MPI agent for positron emission tomography in the future.

Noninvasive imaging of the heart and coronary arteries

There are multiple imaging modalities currently available to noninvasively evaluate the heart and coronary arteries. Choosing the most appropriate modality depends on the pertinent clinical question and the underlying patient characteristics. This article provides an overview of the fields of echocardiography, myocardial perfusion imaging, cardiac computed tomography, and cardiac magnetic resonance imaging, with particular attention to specific clinical applications for cardiac surgery patients.

Impact of ACE and ApoE polymorphisms on myocardial perfusion: correlation with myocardial single photon emission computed tomographic imaging

Coronary artery disease is associated with multiple genetic and environmental risk factors. In this study, we evaluated the correlation of angiotensin l-converting enzyme (ACE) (I/D) and ApoE gene polymorphisms (E2, E3, E4 and g.-219G/T) with myocardial perfusion. We examined 410 patients using exercise-rest myocardial perfusion single photon emission computed tomography (SPECT), in which the summed stress score (SSS), summed rest score (SRS) and summed difference score (SDS) indexes were calculated. Homozygotes for the ACE D allele had greater mean values of SSS (P<0.001) and SDS (P<0.001). In addition, E3 homozygotes, E4 heterozygotes and E4 homozygotes had significantly higher values of SSS and SDS compared with E3 heterozygotes (P<0.001); E4 homozygotes had significantly higher values of SSS and SDS compared with E3 homozygotes. Furthermore, for the g.-219G>T polymorphic site at the promoter region of ApoE gene, the mean values of SSS and SDS were significantly higher for T heterozygotes/homozygotes than for GG homozygotes. Adjusting for all demographic and clinical data using multiple linear regression analysis it was found that ACE D and both ApoE genotypes were independent predictors with a cumulative contribution for the prediction of SSS and SDS. Furthermore, logistic regression analysis revealed that all three genotypes had an independent predictive ability for abnormal SSS (SSS>2). These data provide the first evidence of an association and significant cumulative contribution of the aforementioned genotypes in myocardial perfusion with E4 allele having the strongest association followed by ACE D and ApoE g.-219T alleles.

Mechanism for myocardial localization and rapid liver clearance of Tc-99m-N-MPO: a new perfusion radiotracer for heart imaging

BACKGROUND

[Tc-99m-N(mpo)(PNP5)](+) (Tc-99m-N-MPO: Hmpo = 2-mercaptopyridine N-oxide and PNP5 = N-ethoxyethyl-N,N-bis[2-(bis(3-methoxypropyl)phosphino)ethyl]amine) is a new Tc-99m radiotracer useful for myocardial perfusion imaging. The main objective of this study is to elucidate the mechanism for myocardial localization and fast liver clearance of Tc-99m-N-MPO in comparison with Tc-99m-sestamibi ([Tc-99m-(MIBI)(6)](+): MIBI = 2-methoxy-2-methylpropylisonitrile).

METHODS AND RESULTS

Subcellular distribution of Tc-99m-N-MPO and Tc-99m-sestamibi was examined in the excised Sprague-Dawley (SD) rat myocardium. Biodistribution and planar imaging studies were performed using SD rats in the absence/presence of Cyclosporin-A. Due to negative plasma and mitochondrial potentials, 84.5% +/- 3.2% of Tc-99m-N-MPO was found in the mitochondrial fraction as compared to 88.0% +/- 1.5% of Tc-99m-sestamibi. There was no significant difference in their mitochondrial accumulation. Tc-99m-N-MPO was also able to retain its chemical integrity in rat myocardium. Pre-treatment of SD rats with Cys-A result in significant increase in the kidney and liver uptake of Tc-99m-N-MPO.

CONCLUSION

Tc-99m-N-MPO and Tc-99m-sestamibi share almost identical subcellular distribution and localization mechanism. The MDR transport function of hepatocytes and renal cells is responsible for the fast clearance kinetics of Tc-99m-N-MPO from liver and kidneys, respectively. Tc-99m-N-MPO is a very promising myocardial perfusion radiotracer with favorable biodistribution properties and rapid liver clearance.

Myocardial 18F-FDG uptake after exercise-induced myocardial ischemia in patients with coronary artery disease

We have recently demonstrated the potential of (18)F-FDG as an imaging marker of myocardial ischemia if injected at peak exercise. However, how long increased (18)F-FDG uptake can be observed after an episode of exercise-induced myocardial ischemia is not known. We performed the current study to determine whether increased regional myocardial (18)F-FDG uptake at exercise in patients with coronary artery disease (CAD) persists on rest imaging (24 h later), after an episode of exercise-induced myocardial ischemia.

METHODS

Twenty-four patients with suspected CAD underwent exercise (99m)Tc-sestamibi and (18)F-FDG imaging. Repeated (18)F-FDG imaging was performed 24 h after exercise imaging, after an injection of a second dose of (18)F-FDG at rest in 20 patients. Perfusion imaging with (99m)Tc-sestamibi was simultaneously performed with (18)F-FDG imaging. All patients underwent coronary angiography.

RESULTS

Eighteen patients had greater than or equal to 70% luminal narrowing of 1 or more coronary vessels. Fifteen patients (83%) showed increased regional (18)F-FDG uptake on exercise imaging, but only 11 patients (61%) had perfusion abnormalities. Of these 15 patients with increased regional (18)F-FDG uptake on exercise imaging, 8 (53%) had no discernible (18)F-FDG uptake, 5 (33%) had decreased (18)F-FDG uptake, and only 2 (13%) had persistent (18)F-FDG uptake on rest (18)F-FDG images. The summed (18)F-FDG uptake score significantly decreased, from 14.4 +/- 10.3 at exercise to 6.7 +/- 9.2 at rest (P = 0.01). Patients with persistent (18)F-FDG uptake at rest had more (18)F-FDG uptake and lower peak rate-pressure product at exercise, compared with patients with no residual (18)F-FDG uptake at rest.

CONCLUSION

Exercise-induced regional myocardial (18)F-FDG uptake is highly specific and sensitive for exercise-induced myocardial ischemia. Regional myocardial (18)F-FDG uptake may persist 24 h after an episode of exercise-induced myocardial ischemia in some patients.

Evaluation of 99mTcN-15C5 as a new myocardial perfusion imaging agent in normal dogs and canines with coronary stenosis

OBJECTIVES

This study was designed to evaluate the biodistribution and blood clearance characteristics of 99mTcN-15C5 and its potential as a myocardial perfusion radiotracer.

METHODS

Five normal mongrel dogs were injected with 99mTcN-15C5 intravenously. Blood samples were collected at 0.5, 1, 2, 3, 4, 5, 10, 15, and 30 min postinjection (p.i.). Anterior planar images were acquired at 5, 15, 30, 60, 90, and 120 min p.i. Regions of interest (ROIs) were drawn around heart, liver, and lungs. The raw activity in each ROI was expressed as counts/pixel/min. Heart/liver and heart/lung ratios were calculated by dividing the mean counts in heart ROI by the mean counts in liver and lung ROI, respectively. For comparison, 99mTc-sestamibi was also evaluated in the same five dogs. In dogs with coronary stenoses, single photon emission computed tomography images were acquired at 30, 60, and 120 min after administration of 99mTcN-15C5 with/without adenosine.

RESULTS

99mTcN-15C5 and 99mTc-sestamibi had very similar blood clearance characteristics during the first 30 min p.i. The heart/liver ratio of 99mTcN-15C5 increased from 0.48+/-0.05 at 5 min p.i. to 1.85+/-0.11 at 120 min p.i., whereas the heart/liver ratio of 99mTc-sestamibi was improved only slightly from 0.45+/-0.04 at 5 min p.i. to 0.74+/-0.15 at 120 min p.i. SPECT imaging studies in canines with coronary stenoses indicated that good visualization of the perfusion defect could be achieved at 30 min after administration of 99mTcN-15C5 with the adenosine stress.

CONCLUSION

The combination of high heart uptake and rapid liver clearance makes 99mTcN-15C5 a promising new radiotracer for myocardial perfusion imaging.

Myocardial perfusion imaging with contrast echocardiography

Advances in myocardial perfusion imaging have firmly established the use of noninvasive techniques capable of providing useful information over a broad range of diagnostic and therapeutic cardiovascular problems. Evaluating regional myocardial perfusion abnormalities is a cornerstone for the diagnosis of coronary artery disease, risk assessment in those with known disease, and determination of myocardial viability. The clinical use of myocardial perfusion imaging and the current limitations of existing techniques continue to promote the development of new technologies capable of assessing microvascular and capillary perfusion abnormalities on a global myocardial level. Myocardial contrast echocardiography is an emerging technique capable of rapidly assessing myocardial perfusion at the capillary level in many different clinical settings. This article focuses on myocardial contrast-enhanced ultrasound perfusion techniques, emphasizing the unique information this modality provides compared with other noninvasive perfusion imaging techniques.

Synthetic approaches to heterocyclic ligands for Gd-based MRI contrast agents

Magnetic Resonance Imaging (MRI) methods are currently used in the clinic for the non invasive detection and characterization of a wide variety of pathologies. Increases in the diagnostic efficiency of MRI have been helped by both the design of dedicated MR sequences revealing specific aspects of the pathology and by the development of more sensitive and selective Contrast Agents (CAs), capable of more precisely delineating the borderline regions. In the present review we focus on the synthetic strategies used to obtain MRI CAs containing heterocyclic rings.