Purpose:To improve the quantification of myocardial perfusion by registering the time series of magnetic resonance (MR) images with injection of gadolinium. Materials and Methods:Eight patients underwent MR scans to perform myocardial perfusion exam. Two short axis views of the left ventricle (LV) were acquired in free breathing. Two masks for performing the spatial registration of the images were evaluated. The registration was based on pixel intensity in a multi-resolution scheme. The efficiency of this correction was evaluated by calculating geometric residual displacement of the LV and by fitting the data to a compartment model fit with two parameters: K1, the blood-to-myocardium transfer coefficient, and Vd, the distribution volume of the contrast media. Results:The registration stage allowed a decrease in the observed motion of the LV from more than 1.98 Ϯ 0.68 mm to less than 0.56 Ϯ 0.18 mm (mean Ϯ SD). Variability obtained in the perfusion analysis decreased from 46 Ϯ 103% to 5Ϯ 4% for K1 parameter and from 18 Ϯ 21% to 5 Ϯ 5% for Vd parameter. Conclusion:As with manual correction, this automatic motion correction leads to accurate perfusion parameters in dynamic cardiac MR imaging after contrast agent injection. This automatic stage requires placing only one mask over one frame of the perfusion study instead of manually shifting each image to fit a reference image of the perfusion study.

Rationale and Objectives:To investigate the transport of the hepatobiliary magnetic resonance (MR) imaging contrast agent Gd-BOPTA into rat hepatocytes. Materials and Methods:In a MR-compatible hollow-fiber bioreactor containing hepatocytes, MR signal intensity was measured over time during the perfusion of Gd-BOPTA. For comparison, the perfusion of an extracellular contrast agent (Gd-DTPA) was also studied. A compartmental pharmacokinetic model was developed to describe dynamic signal intensity-time curves. Results: The dynamic signal intensity-time curves of the hepatocyte hollow-fiber bioreactor during Gd-BOPTA perfusion were adequately fitted by 2 compartmental models. Modeling permitted to discriminate between the behaviors of the extracellular contrast agent (Gd-DTPA) and the hepatobiliary contrast agent (Gd-BOPTA). It allowed the successfully quantification of the parameters involved in such differences. Gd-BOPTA uptake was saturable at high substrate concentrations. Conclusions: The transport of Gd-BOPTA into rat hepatocytes was successfully described by compartmental analysis of the signal intensity recorded over time and supported the hypothesis of a transporter-mediated uptake.

Global left ventricular function is a prognostic indicator and is used to evaluate therapeutical interventions in patients with heart failure. Regional left ventricular function can be determined with tagged MRI. Assessment of global left ventricular function using the tagging data may have additional clinical value without incurring extra scanning time, which is currently a limiting factor in cardiac imaging. Direct determination of end-diastolic volume is not possible with conventional tagged MRI. However, end-systolic volume can be directly measured because myocardium-blood contrast improves through a tagged image series. We investigated the potential of tagged MRI using frequency-domain analysis software to retrospectively track end-diastolic contour from endsystolic contour and subsequently calculate the ejection fraction. Tagged MRI was compared with the standard bright-blood cine MRI in healthy volunteers (n=20) and patients with previous myocardial infarction (n=8). Left ventricular ejection fraction derived from tagged MRI is linearly correlated to left ventricular ejection fraction obtained by standard cardiac cine MRI (y=1.0x+1.31, r>0.98, p=0.014). In addition, the inter-observer and intra-observer coefficient of variation for left ventricular ejection fraction measurements was low (CV intra =0.4%, CV inter =1.3%). With tagged MRI, only end-systolic volume needs to be manually determined, and accurate estimation of left ventricular ejection fraction is obtained because end-diastolic and end-systolic volumes are determined using identical anatomical points. Our data indicate that tagged MRI can be used to quantitatively assess both regional and global left ventricular function. Therefore, tagged MRI may be a valuable clinical tool for determining the prognosis and evaluating the effect of therapeutical intervention using a single imaging session in patients with left ventricular dysfunction.

Very user-friendly software was developed. The manipulator needs to scan the radiographs only one time. The software performs all subsequent processing steps.

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The new high performance radioisotopic imager IRIS we recently developed has an intrinsic spatial resolution of about 1 .7 mm. To obtain a good sensitivity, it is necessary to use a collimator with holes greater than this spatial resolution.However, this induces artifacts in images. In this paper, we describe a new concept: a moving collimator. Deterministic and Monte Carlo simulations demonstrate that it is possible to obtain simultaneously global high spatial resolution and good sensitivity in radioisotopic imaging.

Radioisotopic investigations are very useful for functional diagnosis, but available gamma cameras have poor spatial resolution. Development of new PSPMT based highresolution detectors brings new interests to this medical imaging technique.