A simplified intravenous glucose loading protocol for fluorine-18 fluorodeoxyglucose cardiac single-photon emission tomography

Status of F-18 fluorodeoxyglucose uptake in normal and hibernating myocardium after glucose and insulin loading

Objective

F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) has been increasingly used in myocardial viability imaging. In routine PET viability studies, oral glucose and intravenous insulin loading is commonly utilized. In an optimal study, glucose and insulin loading is expected to cause FDG uptake both in hibernating and normal myocardium. However, in routine studies it is not uncommon to see absent or reduced FDG uptake in normal myocardium. In this retrospective study we further analyzed our PET viability images to evaluate FDG uptake status in myocardium under the oral glucose and intravenous insulin loading protocol that we use in our hospital.

Methods

Patients who had both myocardial perfusion single photon emission computed tomography (SPECT) and FDG PET cardiac viability studies were selected for analysis. FDG uptake status in normal and abnormal myocardial segments on perfusion SPECT was evaluated. Based on SPECT and PET findings, patients were divided into two main groups and four subgroups. Group 1 included PET viable studies and Group 2 included PET-nonviable studies. Subgroups based on FDG uptake in normal myocardium were 1a and 2a (normal uptake) and 1b and 2b (absent or significantly reduced uptake).

Results

Seventy-one patients met the inclusion criteria. Forty-two patients were PET-viable and 29 were PET-nonviable. In 33 of 71 patients (46.4%) there was absent or significantly reduced FDG uptake in one or more normal myocardial segments, which was identified more in PET-viable than PET-nonviable patients (59.5% vs. 27.5%, p = 0.008). This finding was also more frequent in diabetic than nondiabetic patients (53% vs. 31.8%), but the difference was not significant (p = 0.160).

Conclusions

In nearly half of our patients, one or more normal myocardial segments showed absent or significantly reduced FDG uptake. This finding, particularly if it is diffuse, could be from suboptimal study, inadequacy of current glucose and insulin loading protocols, or various other patient-related causes affecting FDG uptake both in the normal and hibernating myocardium. In cases with significantly reduced FDG uptake in normal myocardium, PET images should be interpreted cautiously to prevent false-negative results for viability.

Simplified protocol of cardiac 18F-fluorodeoxyglucose positron emission tomography viability study in normoglycemic patients with known coronary artery disease

PURPOSE

The purpose was to evaluate quality of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) myocardial scans and its correlation with background glucose (BG) after simplified 5% intravenous glucose load protocol.

METHODS

An intravenous glucose load protocol was applied in 69 normoglycemic patients with confirmed coronary artery disease. The blood glucose level was measured every 15 min.

RESULTS

Eighty-four percent of images were optimal, 8.7% suboptimal, and 7.3% uninterpretable. The quality of 18F-FDG-PET was BG independent and body mass index dependent (P=.0007).

CONCLUSIONS

Simplified glucose load protocol is a safe and efficient method of preparation for FDG cardiac viability study in patients with normoglycemia.

Enhancing the [13C]bicarbonate signal in cardiac hyperpolarized [1-13C]pyruvate MRS studies by infusion of glucose, insulin and potassium

A change in myocardial metabolism is a known effect of several diseases. MRS with hyperpolarized (13)C-labelled pyruvate is a technique capable of detecting changes in myocardial pyruvate metabolism, and has proven to be useful for the evaluation of myocardial ischaemia in vivo. However, during fasting, the myocardial glucose oxidation is low and the fatty acid oxidation (β-oxidation) is high, which complicates the interpretation of pyruvate metabolism with the technique. The aim of this study was to investigate whether the infusion of glucose, insulin and potassium (GIK) could increase the myocardial glucose oxidation in the citric acid cycle, reflected as an increase in the [(13)C]bicarbonate signal in cardiac hyperpolarized [1-(13)C]pyruvate MRS measurements in fasted rats. Two groups of rats were infused with two different doses of GIK and investigated by MRS after injection of hyperpolarized [1-(13)C]pyruvate. No [(13)C]bicarbonate signal could be detected in the fasted state. However, a significant increase in the [(13)C]bicarbonate signal was observed by the infusion of a high dose of GIK. This study demonstrates that a high [(13)C]bicarbonate signal can be achieved by GIK infusion in fasted rats. The increased [(13)C]bicarbonate signal indicates an increased flux of pyruvate through the pyruvate dehydrogenase enzyme complex and an increase in myocardial glucose oxidation through the citric acid cycle.

A novel clinical method for quantification of regional left ventricular pressure-strain loop area: a non-invasive index of myocardial work

Aims

Left ventricular (LV) pressure–strain loop area reflects regional myocardial work and metabolic demand, but the clinical use of this index is limited by the need for invasive pressure. In this study, we introduce a non-invasive method to measure LV pressure–strain loop area.

Methods and results

Left ventricular pressure was estimated by utilizing the profile of an empiric, normalized reference curve which was adjusted according to the duration of LV isovolumic and ejection phases, as defined by timing of aortic and mitral valve events by echocardiography. Absolute LV systolic pressure was set equal to arterial pressure measured invasively in dogs (n = 12) and non-invasively in patients (n = 18). In six patients, myocardial glucose metabolism was measured by positron emission tomography (PET). First, we studied anaesthetized dogs and observed an excellent correlation (r = 0.96) and a good agreement between estimated LV pressure–strain loop area and loop area by LV micromanometer and sonomicrometry. Secondly, we validated the method in patients with various cardiac disorders, including LV dyssynchrony, and confirmed an excellent correlation (r = 0.99) and a good agreement between pressure–strain loop areas using non-invasive and invasive LV pressure. Non-invasive pressure–strain loop area reflected work when incorporating changes in local LV geometry (r = 0.97) and showed a strong correlation with regional myocardial glucose metabolism by PET (r = 0.81).

Conclusions

The novel non-invasive method for regional LV pressure–strain loop area corresponded well with invasive measurements and with directly measured myocardial work and it reflected myocardial metabolism. This method for assessment of regional work may be of clinical interest for several patients groups, including LV dyssynchrony and ischaemia.

Role of F-18 FDG positron emission tomography (PET) in the assessment of myocardial viability

Positron emission tomography (PET) is a functional imaging technique with important clinical applications in cardiology, oncology, and neurology. In cardiac imaging, its role has been extensively evaluated in the noninvasive diagnosis of coronary artery disease and in the determination of prognosis. Additionally, cardiac PET with F-18 fluorodeoxyglucose (FDG) is very helpful in selection of patients with coronary artery disease and left ventricular dysfunction who would benefit from coronary artery revascularization. Cardiac PET is arguably considered by many as a gold standard in this particular application. F-18, unlike other positron emitters, has a reasonably long physical half-life, which permits its distribution through commercial radiopharmacies. This is further facilitated by increasing popularity of FDG PET in oncology, which makes cardiac FDG PET a practical option for hospitals and outpatient centers equipped with PET scanners. In addition, gamma camera single photon emission computed tomography (SPECT) systems, routinely used in nuclear medicine departments, can be equipped with coincidence circuit or high-energy 511 KeV collimators, providing a cost-effective means of FDG cardiac imaging. Myocardial utilization of glucose as a substrate is variable, depending, among other factors, on serum levels of glucose and insulin. Therefore, patient preparation is important in obtaining good-quality images and in turn allowing for accurate interpretation of myocardial viability. There are various protocols to choose from that provide diagnostic image quality in both diabetic and nondiabetic patients. Mismatch between blood flow and FDG metabolism, an indicator of viable, jeopardized myocardium, can predict postrevascularization improvement in left ventricular function, symptomatic relief, and long-term survival.

Pitfalls and artifacts in 18FDG PET and PET/CT oncologic imaging

It is estimated that in excess of one million positron emission tomography (PET) scans are performed each year and PET can now truly be regarded as a routine imaging procedure in clinical management. Many potential pitfalls and artifacts have previously been described with (18)F-fluorodeoxyglucose PET imaging, but more continue to become apparent as worldwide experience increases. In addition, the advent of combined PET/CT scanners in clinical imaging practice has brought their own specific pitfalls and artifacts. It is essential that we learn these potential pitfalls so that patients can be optimally prepared for their scans and that accurate interpretation can be made.

Comparison of 99mTc-sestamibi-18F-fluorodeoxyglucose dual isotope simultaneous acquisition and rest-stress 99mTc-sestamibi single photon emission computed tomography for the assessment of myocardial viability

Dual isotope simultaneous acquisition single photon emission computed tomography (DISA SPECT) offers the advantage of obtaining information on myocardial perfusion using Tc-sestamibi ( Tc-MIBI) and metabolism using F-fluorodeoxyglucose ( F-FDG) in a single study. The prerequisite is that the Tc-MIBI images are not degraded by scattered 511 keV photons or poor count statistics due to the lower efficiency of the extra high energy (EHE) collimator. Therefore, we compared the registered Tc-MIBI uptake and image quality of DISA and single isotope acquisition. Furthermore, we investigated whether DISA yields additional information for the assessment of myocardial viability in comparison with rest-stress Tc-MIBI. Nineteen patients with known coronary artery disease and irreversible perfusion defects on previous rest-stress MIBI test studies were investigated. After oral glucose loading and simultaneous injection of 600 MBq of Tc-MIBI and 185 MBq of F-FDG at rest, DISA was performed using energy windows of 140 (+/-15%), 170 (+/-20%) and 511 keV (+/-15%). Planar 140 keV images were corrected for scatter by subtraction using the 170 keV window. The single and dual isotope Tc-MIBI images were both displayed in a polar map with 128 segments normalized to maximum counts. F-FDG and Tc-MIBI images were visually scored for a perfusion-metabolism mismatch pattern using nine regions per heart. There was an excellent correlation (r =0.93, P<0.0001) between the Tc-MIBI uptake detected in the single and dual isotope acquisition. The average difference between the dual and single isotope Tc-MIBI uptake was -1.2% (not significantly different from zero) and the coefficient of variation of the difference was 8.7%. Of the 79 regions with irreversible perfusion defects on previous rest-stress Tc-MIBI, six regions in five patients showed a perfusion-metabolism mismatch pattern. We conclude that DISA does not affect the quality of the Tc-MIBI images. Furthermore, F-FDG- Tc-MIBI DISA may show viability in a small but significant (7.6%, P<0.0034) number of regions with irreversible perfusion defects on rest-stress Tc-MIBI.

Safety and feasibility of cardiac FDG SPECT following oral administration of Acipimox, a nicotinic acid derivative: Comparison of image quality with hyperinsulinemic euglycemic clamping in nondiabetic patients

BACKGROUND

Image quality of cardiac fluorine-18-deoxyglucose (FDG) studies is highly dependent on the metabolic conditions during the study; hyperinsulinemic euglycemic clamping ensures adequate image quality. However, the approach is time-consuming. Data in a small number of patients suggest that oral administration of a nicotinic acid derivative (Acipimox, 250 mg; Byk, The Netherlands) results in good image quality.

METHODS AND RESULTS

The safety and image quality of cardiac FDG single photon emission computed tomography studies after Acipimox administration were evaluated (21 patients, group 2); the results were compared with studies performed during hyperinsulinemic euglycemic clamping (69 patients, group 1). Image quality was assessed visually and quantitatively with use of heart-to-lung, heart-to-liver, and myocardium-to-background ratios. Blood samples were drawn at baseline and at the time of FDG injection to determine levels of glucose, free fatty acids, and insulin. Baseline characteristics of group 1 and 2 patients were comparable. No side effects occurred in group 1. Four patients in group 2 (19%) had paroxysmal flushing. Image quality, assessed visually, was good in 100% of group 1 patients and in 86% of group 2 patients. Images were uninterpretable in only 1 patient in group 2 (5%). All quantitative parameters of image quality (heart-to-lung, heart-to-liver, and myocardium-to-background ratios) were comparable between group 1 and 2 patients. Baseline plasma levels of all substrates were comparable between groups. At the time of FDG injection, plasma levels of glucose and free fatty acids were comparable between groups; insulin was higher in group 1 patients.

CONCLUSIONS

Cardiac FDG single photon emission computed tomography after Acipimox is a simple and safe approach that renders comparable image quality to that obtained during hyperinsulinemic euglycemic clamping.

Cardiac nuclear medicine in monitoring patients with coronary heart disease

Patient monitoring is a major indication for cardiac nuclear medicine procedures. Stress myocardial perfusion scintigraphy was initially used for diagnosis, but monitoring patients with coronary artery disease has become more common. Stress myocardial perfusion scintigraphy has been shown to provide a considerable amount of incremental prognostic information, which may be useful in selecting patients for therapy. In patients being considered for revascularization, fluorodeoxyglucose can be used to identify regions of dysfunctional but viable myocardium, even within regions that show fixed defects on stress perfusion imaging. It can be used to select a group of patients who will improve function with revascularization and who may have an improved outcome. Thus, cardiac nuclear medicine plays a pivotal role in monitoring patients with coronary artery disease.

18-Fluorodeoxyglucose imaging with positron emission tomography and single photon emission computed tomography: cardiac applications

The assessment of myocardial viability has become an important aspect of the diagnostic and prognostic work-up of patients with ischemic cardiomyopathy. Although revascularization may be considered in patients with extensive viable myocardium, patients with predominantly scar tissue should be treated medically or evaluated for heart transplantation. Among the many viability tests, noninvasive assessment of cardiac glucose use (as a marker of viable tissue) with F18-fluorodeoxyglucose (FDG) is considered the most accurate technique to detect viable myocardium. Cardiac FDG uptake has traditionally been imaged with positron emission tomography (PET). Clinical studies have shown that FDG-PET can accurately identify patients with viable myocardium that are likely to benefit from revascularization procedures, in terms of improvement of left ventricular (LV) function, alleviation of heart failure symptoms, and improvement of long-term prognosis. However, the restricted availability of PET equipment cannot meet the increasing demand for viability studies. As a consequence, much effort has been invested over the past years in the development of 511-keV collimators, enabling FDG imaging with single-photon emission computed tomography (SPECT). Because SPECT cameras are widely available, this approach may allow a more widespread use of FDG for the assessment of myocardial viability. Initial studies have directly compared FDG-SPECT with FDG-PET and consistently reported a good agreement for the assessment of myocardial viability between these 2 techniques. Additional studies have shown that FDG-SPECT can also predict improvement of LV function and heart failure symptoms after revascularization. Finally, recent developments, including coincidence imaging and attenuation correction, may further optimize cardiac FDG imaging (for the assessment of viability) without PET systems.