Simple quantification of myocardial perfusion by pixel-by-pixel graphical analysis using carbon-11 acetate: comparison of the K-complexes of carbon-11 acetate and nitrogen-13 ammonia

Appropriate parameters of the ordered-subset expectation maximization algorithm on measurement of myocardial blood flow and oxygen consumption with 11C-acetate PET

OBJECTIVE

The purpose of this study was to evaluate the appropriate parameters of a filter and of subsets (S) and iterations (I) of the ordered-subset expectation maximization (OSEM) algorithm in 11C-acetate PET.

METHODS

A Hanning filter (HF) and a Gaussian filter (GF) were selected for filtered back-projection (FBP) and the OSEM algorithm, respectively. After evaluation of the optimal HF size, the GF size was optimized using healthy volunteers (HV). Myocardial blood flow (MBF) and oxygen consumption (k(mono)) values were calculated by combining 4S, 16S, or 28S with 2I, 4I, 6I, or 8I of the OSEM (MBF(OSEM) and k(monoOSEM), respectively) in eight HV and eight coronary artery disease (CAD) patients. These MBF(OSEM) and k(monoOSEM) values were compared with those obtained using FBP (MBF(FBP) and k(monoFBP), respectively).

RESULTS

Optimal HF and GF (10.0GF) sizes for the FBP and OSEM algorithms, respectively, were 10.0 mm full-width resolution at half-maximum. MBF(OSEM) was changed by modifying the parameters of the OSEM algorithm. The best correlations were between MBF(FBP) and MBF(OSEM), with 28S6I and 10.0GF for HV patients and 28S8I for CAD patients. However, the MBF(OSEM) with 28S8I was significantly different from MBF(FBP) at the global myocardium in HV. The k(monoOSEM) with 28S6I was not significantly different from k(monoFBP) in HV or CAD patients.

CONCLUSION

Appropriate parameters are 28S6I with a 10.0GF on the MBF(OSEM) and k(monoOSEM) measurement using 11C-acetate. Diagnostic performance will improve using noiseless, artifact-reduction images, and accurate quantitative values that are provided by the OSEM algorithm with the appropriate parameters.

Abnormal myocardial energy-production state in mitochondrial cardiomyopathy and acute response to L-arginine infusion. C-11 acetate kinetics revealed by positron emission tomography

BACKGROUND

Cardiomyopathy is a life-threatening condition in patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (known as MELAS). However, no effective therapy has been available until now. In the present study cardiac energetics and acute effects of L-arginine (Arg) were evaluated in MELAS patients.

METHODS AND RESULTS

The 6 patients with MELAS (M-group) and 6 volunteers (C-group) underwent dynamic C-11 acetate positron emission tomography (PET) imaging. TCA-cycle metabolic rate (k(mono)), myocardial efficiency (double product (DP)/k(mono)), and myocardial blood flow (MBF) were determined before and after L-Arg administration. Baseline k(mono) showed a lower value in the M-group than in the C-group (0.051±0.013 vs 0.070±0.019min(-1), P=0.055). On the other hand, baseline DP/k(mono) was significantly greater in the M-group (1.69±5.9 vs 0.95±1.2×10(5), P=0.004). After L-Arg administration, 4 patients showed significant elevation of k(mono). No relationship was observed between the distribution of k(mono) elevation and the increase in MBF.

CONCLUSIONS

The TCA cycle metabolic rate is markedly suppressed in MELAS patients, indicating a shift in energy production to the anaerobic pathway, leading to a paradoxical increase in myocardial efficiency. L-Arg can enhance TCA-cycle metabolism, regardless of its vasodilatation effect, and can be used as a treatment for patients with mitochondrial cardiomyopathy.

[¹¹C]acetate PET/CT visualizes skeletal muscle exercise participation, impaired function, and recovery after hip arthroplasty; first results

Purpose

Based on skeletal muscle acetate physiology we aimed studying muscle function after hip arthroplasty with [¹¹C]acetate PET.

Procedures

Two male patients were investigated 3 and 12 weeks after hip arthroplasty with muscle [¹¹C]acetate PET/CT performed at rest and exercise. Median muscle SUV_mean were calculated on three non-consecutive transverse PET slices.

Results

The four exercise PET/CT showed, compared with rest, consistent increase in [¹¹C]acetate uptake in active muscles contralateral to surgery. On the arthroplasty side most muscles showed symmetric activity increase under exercise both at 3 and 12 weeks after surgery, but four muscles showed only minor activity increase at 3 weeks. At 3 months, functional recovery of the latter four muscles was observed.

Conclusion

Consistent increase in [¹¹C]acetate uptake in healthy muscles under exercise compared with rest was observed by PET/CT. Transiently impaired muscle function 3 weeks after surgery recovered at 3 months. These first observations merit further investigation.

Validation of the calculation of the clearance rate constant (k(mono)) of [(11)C]acetate using parametric k(mono) image for myocardial oxidative metabolism

INTRODUCTION

The purpose of this study was to validate the calculation of myocardial oxidative metabolism rate using a parametric clearance rate constant (k(mono)) image.

METHODS

Fifteen subjects (seven volunteers, eight patients) were studied. Dynamic PET was acquired after intravenous injection of 700 MBq of [(11)C]acetate. The clearance rate constant of [(11)C]acetate (k(mono)) was calculated pixel by pixel to generate the parametric k(mono) image. The k(mono) values from this image and those calculated from the dynamic image were compared in the same regions of interest (ROIs).

RESULTS

Two different methods showed an excellent correlation except in the very low range. Regression equations were y=0.99x+0.0034 (r(2)=0.86, P<.001) and y=1.16x-0.0077 (r(2)=0.87, P<.001) in normal volunteer and patient groups, respectively, and y=1.07x-0.0019 (r(2)=0.87, P<.001) when combined.

CONCLUSIONS

Both methods exhibited similar values of k(mono). Parametric k(mono) image may result in better visual understanding of regional myocardial oxidative metabolism.