Acoustic Radiation Force Impulse (ARFI) imaging is a novel ultrasound-based elastography method that is integrated in a conventional ultrasound machine enabling the exact localization of measurement site. It might present an alternative method to transient elastography for the noninvasive assessment of liver fibrosis. At present, studies with small patient population have shown promising results. A systematic review and meta-analysis of pooled patient data were performed to evaluate the overall performance of ARFI for the staging of liver fibrosis. Literature databases were searched up to 10/2010. The authors of the original publication were contacted, and the original patient data were requested. A meta-analysis was performed using a random effect meta-analytic method for diagnostic tests. In addition, available data comparing ARFI with FibroScan with the DeLong test were evaluated. Literature search yielded nine full-paper publications evaluating ARFI while using liver biopsy as reference method. Original patient data were available from eight studies including 518 patients. The mean diagnostic accuracy of ARFI expressed as areas under ROC curves (AUROC) was 0.87 for the diagnosis of significant fibrosis (F ≥ 2), 0.91 for the diagnosis of severe fibrosis (F ≥ 3), and 0.93 for the diagnosis of cirrhosis. ARFI can be performed with good diagnostic accuracy for the noninvasive staging of liver fibrosis.

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The effect of the inaccuracy of the input function on CBF measured by the H2(15)O autoradiographic method was investigated. In H2(15)O autoradiography the measured input function usually includes a larger dispersion than the true input function, as well as the absolute time axis having been already lost. The time constant of the external dispersion that occurred in our continuous sampling system was evaluated as 10-12 s when the dispersion function was approximated by a monoexponential function. The internal dispersion occurring in arterial lines in a human body was evaluated as 4-6 s. Such dispersion, indispensable in a patient study, was found to produce large errors in calculating CBF, e.g., 5(10) s of the dispersion caused +15(33) and +10(20)% systematic overestimations for the 40- and 60-s accumulation time respectively. An analytical correction employing an inverse Laplace transform was applied to clinical CBF studies, and the results were compared with those from the C15O2 steady-state inhalation method. Correction by 10 s in time constant, corresponding to the external dispersion, reduced the overestimation significantly from 70-100% to approximately 20%. Further correction by 5 s, corresponding to the internal dispersion, resulted in a negligible difference (less than a few percent) from the steady-state method.

Ultrasonic ARFI elastography is a novel, non-invasive and reliable method for the assessment of liver fibrosis in patients with chronic liver disease.

An in vivo technique was developed for measuring the absolute myocardial blood flow with H2`50 and dynamic positron-emission tomography. This technique was based on a new model involving the concept of the tissue fraction, which was defined as the fraction of the tissue mass in the volume of the region of interest. The myocardium was imaged dynamically by positron-emission tomography, starting at the time of intravenous bolus injection of 1212O. The arterial input function was measured continuously with a beta-ray detector. A separate image after C`50 inhalation was also obtained for correction of the H2"5O radioactivity in the blood.The absolute myocardial blood flow and the tissue fraction were calculated for 15 subjects with a kinetic technique under region-of-interest analysis. These results seem consistent with their coronary angiographic findings. The mean value of the measured absolute myocardial blood flows in normal subjects was 0.95 0.09 ml/min/g. This technique detected a diffuse decrease of myocardial blood flow in patients with triple-vessel disease. (Circulation 1988;78:104-115) W ith the use of suitable tracers and appropriate mathematical models, positronemission tomography (PET) has the capability ofproviding noninvasive quantitative measurements of physiological functions in organs. However, in the field of cardiac PET, relatively few measurements have been made of the absolute value of the myocardial blood flow (MBF) and metabolism.1,2 The main reason for this concerns the so-called partial volume effect (PVE), 1-6 that is, the spillover effect in radioactivity measurement due to the relatively thin-walled myocardium compared with the spatial resolution of PET,7 and the wall motion of the myocardium. The PVE problem