Measurement of arterial tracer concentrations from cardiac PET images

Determination of the Input Function at the Entry of the Tissue of Interest and Its Impact on PET Kinetic Modeling Parameters

Quantitative positron emission tomography (PET) imaging is employed with several measurement protocols all relying on the a priori determination of the input function (IF). The standard technique to determine IF is by blood sampling. However, a unique IF determined in a subject for a given PET study, either defined by sampling or in the images, and commonly utilized for all analyzed tissues in that study equally at rest and during interventions, is expected to provoke biases in the rate constants and in tissue blood volume. The determination of a specific IF at the site of the tissue to be analyzed enhances PET accuracy and renders PET imaging less invasive.

A real-time follow-up of photodynamic therapy during PET imaging

PURPOSE

To monitor a real-time follow-up of tumor response to photodynamic therapy (PDT) by dynamic 2-deoxy-2-[(18)F]fluoro-d-glucose ((18)FDG) and positron emission tomography (PET) using two photosensitizing drugs in vivo, and to assess their mechanisms of action.

METHODS

Two types of photosensitizers with different action mechanisms were used in rats implanted with two tumors: AlPcS4 mainly affecting the tumor vascular system, and ZnPcS2 largely inducing direct cell kill. Twenty-four hours after administration of either photosensitizer, one tumor served as control while the other was treated with red light during 30min within the 2h PET imaging by infusion of (18)FDG. The usual two-tissue compartment kinetic model was modified to take into account the perturbation of the treatment during imaging.

RESULTS

The illumination of the tumors during PET imaging provoked a net decrease of (18)FDG uptake in tumors treated with AlPcS4 and a near total absence of (18)FDG uptake in tumors treated with ZnPcS2. After the end of illumination, the tumors regained (18)FDG uptake with a more pronounced uptake in the tumors treated with ZnPcS2. The rate constant values of the new (18)FDG kinetic model reflected the response of the tumors to the treatment in both photosensitizers.

CONCLUSIONS

Dynamic PET imaging can be used to quantitatively assess in vivo and in real-time the response of tumors to treatments. It is demonstrated that the 30min of treatment was not sufficient to reduce the activity of the tumors. The technique could be extended to directly monitor the effects of drugs in vivo.

PET/CT challenge for the non-invasive diagnosis of coronary artery disease

This review will focus on the clinical potential of PET/CT for the characterization of cardiovascular diseases. We describe the technical challenges of combining instrumentation with very different imaging performance and discuss the clinical applications in the field of cardiology.

Tracer Kinetic Modeling in PET

Molecular imaging using PET provides a unique tool for noninvasively investigating the biochemistry of living organs. The wide range of radiolabeled molecules makes it possible to explore various biochemical, physiologic, and pharmacologic processes in vivo. Because each radiotracer is characterized by its particular kinetic behavior in the human body, the quantification of this behavior is a critical component for the improvement of imaging protocols and for rapid translation from research and development to the clinic. Suitable image reconstruction algorithms combined with tracer kinetic modeling techniques are needed to assess parametric or quantitative biologic images from the available fourdimensional images. An appropriate mathematical model is generally used to fit the time-activity curves of a region or volume of interest, thus allowing the assessment of biologic parameters.

Role of relative myocardial perfusion reserve for evaluating stenosis severity in patients with single-vessel coronary artery disease using

A statistically significant correlation was observed between the severity of anatomic stenosis and coronary flow reserve in experimental animals. A similar correlation in human coronary artery disease (CAD) was shown using positron emission tomography (PET) and pharmacologic vasodilator stress. The present study tested whether the concept of relative myocardial perfusion reserve (MPR) might be superior to absolute MPR in correlating coronary stenosis determined by quantitative coronary arteriography in patients with single vessel CAD using [13N]ammonia and PET. The study group comprised 21 patients (62 +/-10 years old; 15 men, 6 women) with normal left ventricular function who underwent angioplasty for isolated left anterior descending coronary artery stenosis. Absolute MPR, the ratio of dipyridamole-induced hyperemic blood flow to baseline blood flow by [13N]ammonia PET, and relative MPR, the ratio of MPR in regions supplied by stenosed coronary arteries to MPR in remote regions, were measured before and 3 months after angioplasty. The percent diameter stenosis was also quantified on coronary arteriograms just before the angioplasty and again at 3 months after. The study found that absolute MPR (r=0.755; p<0.0001) and relative MPR (r=0.814; p<0.0001) were inversely and nonlinearly correlated with the percent stenosis on angiography. The fitting curve of the correlation between relative MPR and coronary stenosis on angiography was identical to that observed in animal models. Therefore, relative MPR measured by [13N]ammonia PET more accurately and specifically describes stenosis severity in patients with CAD compared with absolute MPR, probably because of its independence from hemodynamic variations and the effects of coronary risk factors.

Prognostic utility of myocardial blood flow assessed by N-13 ammonia positron emission tomography in patients with idiopathic dilated cardiomyopathy

Previous studies in patients with idiopathic dilated cardiomyopathy (IDC) have suggested that myocardial perfusion is impaired and spatially heterogeneous in such cases. Our objective was to identify any association between an abnormality in myocardial perfusion and the prognosis of patients with IDC. We collected data on N-13 ammonia positron emission tomography (PET) studies performed in 26 patients with IDC (9 nonsurvivors, 17 survivors) and in 8 normal control subjects. Regional myocardial blood flow (rMBF) was quantified using N-13 ammonia positron emission tomography and the Simple flow model. The spatial heterogeneity of myocardial perfusion was assessed by calculating the coefficient of variance of rMBF. Mean rMBF of the survivors was significantly lower (0.54 +/- 0.13 ml/min/g) than that of control subjects (0.66 +/- 0.06 ml/min/g) (p = 0.03 vs control), but did not differ significantly between nonsurvivors (0.58 +/- 0.15 ml/min/g) and control subjects. The coefficient of variance of rMBF was significantly higher in nonsurvivors than in either survivors or control subjects (0.24 +/- 0.08 vs 0.15 +/- 0.08, p = 0.007, and 0.16 +/- 0.05, p = 0.03, respectively). The probability of 3-year survival (Kaplan-Meier method) was 33.0% in subjects whose coefficient of variance of rMBF was above the median compared with 90.0% in subjects whose coefficient of variance of rMBF was below the median (p = 0.01). The probability of 3-year survival did not differ among subjects whose mean rMBF was above versus below the median (61.5% vs 62.9%, respectively). The results suggest that the prognosis of patients with IDC is associated with the spatial heterogeneity of myocardial perfusion, not with initial absolute rMBF.

The local noise property in positron volume imaging and optimal conditions for the signal-to-noise ratio of the 3D reconstructed image

The local noise property of a 3D PET reconstructed image is investigated for a uniform-activity sphere distributed in a constantly attenuating spherical object. The positional dependence of the statistical noise is approximately derived and calculated for some special cases. It is suggested that a larger diameter of the activity sphere causes noise amplification, and the noise property for the large attenuating sphere is close to that for a non-attenuating object with the same total number of measuring counts. By considering noise propagation of two spherical activity distributions, we suggest that the signal-to-noise ratio of the image depends on a set of projection directions and the sizes and intensities of the activity distributions. In a simple case, we derive an optimal value of the maximum acceptance angle for the projection directions to improve the signal-to-noise ratio of the image.