PET imaging during hypoglycaemia to study adipose tissue metabolism

BACKGROUND

Disturbances in adipose tissue glucose uptake may play a role in the pathogenesis of type 2 diabetes, yet its examination by 2-deoxy-2-[¹⁸ F]fluorodeoxyglucose ([¹⁸ F]FDG) PET/CT is challenged by relatively low uptake kinetics. We tested the hypothesis that performing [¹⁸ F]FDG PET/CT during a hypoglycaemic clamp would improve adipose tissue tracer uptake to allow specific comparison of adipose tissue glucose handling between people with or without type 2 diabetes.

DESIGN

We enrolled participants with or without diabetes who were at least overweight, to undergo a hyperinsulinaemic hypoglycaemic clamp or a hyperinsulinaemic euglycaemic clamp (n = 5 per group). Tracer uptake was quantified using [¹⁸ F]FDG PET/CT.

RESULTS

Hypoglycaemic clamping increased [¹⁸ F]FDG uptake in visceral adipose tissue of healthy participants (P = 0.002). During hypoglycaemia, glucose uptake in visceral adipose tissue of type 2 diabetic participants was lower as compared to healthy participants (P < 0.0005). No significant differences were observed in skeletal muscle, liver or pancreas.

CONCLUSIONS

The present findings indicate that [¹⁸ F]FDG PET/CT during a hypoglycaemic clamp provides a promising new research tool to evaluate adipose tissue glucose metabolism. Using this method, we observed a specific impairment in visceral adipose tissue [¹⁸ F]FDG uptake in type 2 diabetes, suggesting a previously underestimated role for adipose tissue glucose handling in type 2 diabetes.

Validation of a High-Resolution, Phase Contrast Cardiovascular Magnetic Resonance Sequence for Evaluation of Flow in Coronary Artery Bypass Grafts

The aim was to validate a magnetic resonance high-resolution, phase-contrast sequence for quantifying flow in small and large vessels and to demonstrate its feasibility to measure flow in coronary artery bypass grafts. A breathhold, echo planar imaging (EPI) sequence was developed and validated in a flow phantom using a fast field echo (FFE) sequence as reference. In 17 volunteers aortic flow was measured using both sequences. In 5 patients flow in the left internal mammary artery (LIMA) and aorta was measured at rest and during adenosine stress, and coronary flow reserve (CFR) was calculated; in 7 patients, vein graft flow velocity was measured. In the flow phantom measurements, the EPI sequence yielded an excellent correlation with the FFE sequence (r = 0.99; p < 0.001 for all parameters). In healthy volunteers, aortic volume flow correlated well (r = 0.88; p < 0.01), with a minor overestimation. It was feasible to measure flow velocity in the LIMA and vein grafts of the 12 patients. The high-resolution, breathhold cardiovascular magnetic resonance velocity-encoded sequence correlated well with a free-breathing, FFE sequence in a flow phantom and in the aortae of healthy volunteers. Using the EPI sequence, it is feasible to measure flow velocity in both LIMA and vein grafts, and in the aorta.

Assessment of left ventricular volumes and ejection fraction with 16-slice multi-slice computed tomography; comparison with 2D-echocardiography

BACKGROUND

In recent years, multi-slice computed tomography (MSCT) has emerged as a rapidly expanding modality for non-invasive assessment of coronary artery disease. Simultaneously, left ventricular (LV) function can be evaluated although this is not yet a routine component of an MSCT examination. Accordingly, the purpose of the present study was to validate assessment of LV function with MSCT using 2D-echocardiography in a large cohort of patients.

METHODS

In 70 patients (57 male, 13 female), 16-slice MSCT was performed (Toshiba Aquilion 16, Japan) followed by retrospective analysis of global LV function. For these measurements, 2D-echocardiography served as the standard of reference.

RESULTS

For LV volumes, excellent correlations for both end-diastolic volume (EDV) (r=0.97) and end-systolic volume (ESV) (r=0.98) were obtained by linear regression analysis. At Bland-Altman analysis, mean differences (+/-standard deviations) of -1.4 ml+/-11.3 ml and -3.0 ml+/-7.7 ml were observed between MSCT and 2D-echocardiography for LV EDV and LV ESV respectively. As a result, LV EF was slightly overestimated with MSCT (1.7%+/-4.9%, P<0.05). Correlation between the two techniques was excellent (r=0.91).

CONCLUSION

In a large cohort of patients, an excellent correlation was observed between 16-slice MSCT and 2D-echocardiography in the evaluation of LV volumes and EF. The addition of LV function analysis to the anatomical MSCT data may potentially enhance the diagnostic and prognostic value of the technique.

Global and regional left ventricular function assessment with 16-detector row CT: Comparison with echocardiography and cardiovascular magnetic resonance

AIMS

To compare multidetector row computed tomography (MDCT) global and regional left ventricular (LV) function assessment with echocardiography and cardiovascular magnetic resonance (CMR).

METHODS AND RESULTS

In 25 patients, who were referred for noninvasive angiography with 16-detector row CT, LV function assessment was also performed. A subsequent echocardiogram was performed, and in a subgroup of patients, CMR examination was completed to evaluate LV function. For global function assessment, the LV ejection fraction (LVEF) was calculated. Regional LV function was scored using a 17-segment model and a 4-point scoring system. MDCT agreed well with echocardiography for the assessment of LVEF (r=0.96; bias 0.54%; p<0.0001) and regional LV function (kappa=0.78). Eight patients had no contra-indications and gave informed consent for CMR examination. A fair correlation between MDCT and CMR was demonstrated in the assessment of LVEF (r=0.86; bias -1.5%; p<0.01). Regional LV function agreement between MDCT and CMR was good (kappa=0.86).

CONCLUSION

MDCT agreed well with both echocardiography and CMR in the assessment of global and regional LV function. Global and regional LV function may accurately be evaluated by 16-detector row CT, and can be added to a routine CT image analysis protocol without need for additional contrast or imaging time.

Comprehensive assessment of patients after coronary artery bypass grafting by 16-detector-row computed tomography

BACKGROUND

Multidetector-row computed tomography (MDCT) is a versatile modality to evaluate stenoses in native coronary arteries and bypass grafts. Acquired MDCT data can additionally be used to assess left ventricular ejection fraction (LVEF). The purpose was to use MDCT for the assessment of bypass graft and coronary artery disease combined with evaluation of LVEF.

METHODS

Twenty-five patients underwent 16-detector-row CT examination and coronary angiography. Bypass grafts and nongrafted coronary artery segments at MDCT were evaluated on eligibility, patency, and > or = 50% stenosis. The MDCT data set was used to calculate LVEF and was divided into patients with no/subendocardial/transmural myocardial infarctions (MIs).

RESULTS

Ninety vessels were evaluated: 14 arterial grafts/53 vein grafts/23 nongrafted vessels. Of 225 segments, 17 were ineligible for evaluation because of metal clips. With MDCT, patency in segments of arterial grafts/vein grafts/nongrafted vessels could be evaluated with high accuracy in 100%/100%/97% of segments. In arterial grafts, stenoses > or = 50% did not occur at angiography, which was for all eligible segments correctly diagnosed at MDCT. Stenosis > or = 50% could be correctly detected by MDCT with a sensitivity/specificity of 100%/94% for vein grafts and 100%/89% for nongrafted vessels. Negative predictive value was 100% for vein grafts and nongrafted vessels. In patients with transmural MI, MDCT revealed a significant lower LVEF as compared with patients without or with subendocardial MI (P < .05).

CONCLUSION

Comprehensive assessment of bypass grafts, nongrafted vessels, and LVEF is feasible with MDCT. Owing to the high negative predictive value this noninvasive approach may be used as gatekeeper before coronary angiography.

Evaluation of saphenous vein coronary artery bypass graft flow by cardiovascular magnetic resonance

Cardiovascular magnetic resonance (CMR) with flow velocity mapping has emerged as a noninvasive method to measure flow in saphenous vein coronary artery bypass grafts. The aim of the current study was to retrospectively test two previously described analysis methods on a large CMR data set and to compare their diagnostic accuracy in detecting diseased vein grafts. In 125 vein grafts of 68 patients, volume flow parameters (volume flow, systolic and diastolic peak flow, diastolic-to-systolic flow ratio at rest and during adenosine stress, and flow reserve) were derived from the velocity maps. Method 1 implemented basal flow < 20 ml/min or flow reserve < 2, yielding a sensitivity and specificity of 70% and 38% in the detection of a diseased graft or recipient vessel. Method 2 used receiver operating characteristic (ROC) curve analysis and implemented all significant volume flow parameters in a logistic regression model, yielding a sensitivity of 74% with a specificity of 68% in the detection of a diseased graft or recipient vessel. Evaluating single and sequential grafts separately, this method yielded a sensitivity and specificity of 79% and 87% for single grafts, and 62% and 94% for sequential grafts in the detection of > or = 50% stenosis in grafts or recipient vessels. Cut-off values were formulated for the respective volume flow parameters, which maximally separate grafts with and without > or = 50% stenosis. Using ROC curve analysis with logistic regression the specificity of the analysis method improved considerably. For the current data set the best results were acquired when single and sequential grafts were separately analyzed.

Hemodynamic evaluation of saphenous vein coronary artery bypass grafts: Relative merits of Doppler flow velocity and SPECT perfusion imaging

BACKGROUND

Coronary angiography is considered the gold standard in evaluating vein graft disease; however, angiography does not allow assessment of hemodynamic consequences of lesions. In this study hemodynamic consequences of significant stenoses in vein grafts were evaluated by Doppler velocity assessment, and results were compared with single photon emission computed tomography (SPECT) perfusion imaging.

METHODS AND RESULTS

Angiography was performed in 58 patients after coronary artery bypass grafting because of recurrent chest pain. During the procedure, Doppler velocity measurements were acquired before and after administration of adenosine. Of 58 patients (with 78 vein grafts), 20 patients (with 24 vein grafts) underwent SPECT perfusion imaging. Grafts were divided into those with nonsignificant percent diameter stenosis (< 50%) (n = 49) and those with significant percent diameter stenosis (> or =50%) (n = 29). When a cutoff value for coronary flow velocity reserve (CFVR) of 1.8 was applied, modest agreement (69%, kappa = 0.25, P < .05) between CFVR and angiography was shown. Agreement between SPECT and angiography was also modest (63%, kappa = 0.28, P = not significant). SPECT and CFVR provided comparable information in 20 of 24 grafts with available SPECT, illustrating good agreement (83%, kappa = 0.61, P = .001).

CONCLUSIONS

Significant stenoses in vein grafts require further exploration to assess their hemodynamic significance. The Doppler velocity results agreed better with SPECT perfusion imaging than with percent diameter stenosis in the evaluation of vein graft function.

Noninvasive coronary imaging and assessment of left ventricular function using 16-slice computed tomography

In recent years, multislice computed tomography (MSCT) has been demonstrated to be a feasible imaging modality for noninvasive coronary angiography and left ventricular function analysis. The present study evaluated overall performance of 16-slice MSCT in the detection of significant coronary artery disease, stent, or bypass graft stenosis in combination with global left ventricular function analysis. Forty-five patients underwent 16-slice MSCT. Multislice computed tomograms were used to evaluate the presence of significant coronary artery stenoses (>/=50% decrease in luminal diameter) in native coronary segments, bypass grafts, and coronary stents and were compared with conventional coronary angiograms. In addition, left ventricular ejection fraction was calculated and compared with 2-dimensional echocardiography. MSCT was performed successfully in all patients. A close correlation between MSCT and 2-dimensional echocardiography was demonstrated for the assessment of left ventricular ejection fraction (y = 0.93x +3.33, r = 0.96, p <0.001). A total of 298 of native coronary artery segments (94%) were evaluated with MSCT, whereas 81 of 94 grafts (85%) and 41 of 52 coronary stents (79%) were also evaluated. For all segments, overall sensitivity, specificity, and positive and negative predictive values were 85%, 89%, 71%, and 95%, respectively. In conclusion, 16-slice MSCT is a feasible modality for noninvasive evaluation and exclusion of coronary artery disease in patients who present with chest pain.

Functional significance of stenoses in coronary artery bypass grafts. Evaluation by single-photon emission computed tomography perfusion imaging, cardiovascular magnetic resonance, and angiography

OBJECTIVES

This study was designed to perform a head-to-head comparison between single-photon emission computed tomography (SPECT) and cardiovascular magnetic resonance (CMR) to evaluate hemodynamic significance of angiographic findings in bypass grafts.

BACKGROUND

The hemodynamic significance of a bypass graft stenosis may not always accurately be determined from the coronary angiogram. A variety of diagnostic tests (invasive or noninvasive) can further characterize the hemodynamic consequence of a lesion.

METHODS

Fifty-seven arterial and vein grafts in 25 patients were evaluated by angiography, SPECT perfusion imaging, and coronary flow velocity reserve determination by CMR. Based on angiography and SPECT, four different groups could be identified: 1) no significant stenosis (<50%), normal perfusion; 2) significant stenosis (>/=50%), abnormal perfusion; 3) significant stenosis, normal perfusion (no hemodynamic significance); and 4) no significant stenosis, abnormal perfusion (suggesting microvascular disease).

RESULTS

A complete evaluation was obtained in 46 grafts. Single-photon emission computed tomography and CMR provided similar information in 37 of 46 grafts (80%), illustrating good agreement (kappa = 0.61, p < 0.001). Eight grafts perfused a territory with scar tissue. When agreement between SPECT and CMR was restricted to grafts without scar tissue, it improved to 84% (kappa = 0.68). Integration of angiography with SPECT categorized 14 lesions in group 1, 23 in group 2, 6 in group 3, and 3 in group 4. Single-photon emission computed tomography and CMR agreement per group was 86%, 78%, 100%, and 33%, respectively.

CONCLUSIONS

Head-to-head comparison showed good agreement between SPECT and CMR for functional evaluation of bypass grafts. Cardiovascular magnetic resonance may offer an alternative method to SPECT for functional characterization of angiographic lesions.

Noninvasive angiography and assessment of left ventricular function using multislice computed tomography in patients with type 2 diabetes

OBJECTIVE

Early identification of coronary artery disease (CAD) in patients with diabetes is important because these patients are at increased risk for CAD and have worse outcome than nondiabetic patients after CAD is diagnosed. Recently, noninvasive coronary angiography and assessment of left ventricular function has been demonstrated with multislice computed tomography (MSCT). The purpose of the present study was to validate this approach in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

MSCT was performed in 30 patients with confirmed type 2 diabetes. From the MSCT images, coronary artery stenoses (> or =50% luminal narrowing) and left ventricular function (left ventricular ejection fraction, regional wall motion) were evaluated and compared with results of conventional angiography and two-dimensional echocardiography.

RESULTS

Two hundred twenty of 256 coronary artery segments (86%) were interpretable with MSCT. In these segments, sensitivity and specificity for detection of coronary artery stenoses were 95%. Including the uninterpretable segments, sensitivity and specificity were 81 and 82%, respectively. Bland-Altman analysis in the comparison of left ventricular ejection fractions demonstrated a mean difference of -0.48 +/- 3.8% for MSCT and echocardiography, which was not significantly different from 0. Agreement between the two modalities for assessment of regional contractile function was excellent (91%, kappa statistic 0.81).

CONCLUSIONS

Accurate noninvasive evaluation of both the coronary arteries and left ventricular function with MSCT is feasible in patients with type 2 diabetes. This noninvasive approach may allow optimal identification of high-risk patients.

Blood Flow in Coronary Artery Bypass Vein Grafts: Volume versus Velocity at Cardiovascular MR Imaging

Forty-nine patients with previous bypass surgery underwent coronary angiography and cardiovascular magnetic resonance (MR) imaging of single-vein bypass grafts. Volume flow and velocity analyses were performed and compared on MR velocity maps. Bland-Altman analysis showed close agreement between the two types of analysis. Comparison of areas under the receiver operating characteristic curve revealed no significant differences between the analyses for detection of stenoses of 70% or greater. Diagnostic accuracy for volume flow and velocity parameters was 92% and 93%, respectively. Velocity analysis appears to be the preferred method, because it is less time-consuming and has a similar diagnostic accuracy to volume flow analysis.