A 3D high-resolution gamma camera for radiopharmaceutical studies with small animals.

The results of studies conducted with a small field of view tomographic gamma camera based on a Position Sensitive Photomultiplier Tube are reported. The system has been used for the evaluation of radiopharmaceuticals in small animals. Phantom studies have shown a spatial resolution of 2mm in planar and 2-3mm in tomographic imaging. Imaging studies in mice have been carried out both in 2D and 3D. Conventional radiopharmaceuticals have been used and the results have been compared with images from a clinically used system.

Improving spatial resolution in SPECT with the combination of PSPMT based detector and iterative reconstruction algorithms.

This paper investigates the possibility of developing a SPECT system that combines the high spatial resolution of position sensitive photomultiplier tubes (PSPMTs) with the excellent performance of iterative reconstruction algorithms. A small field of view (FOV) camera based on a PSPMT and a pixelized scintillation crystal made of CsI(Tl) have been used for the acquisition of the projections. With the use of maximum likelihood expectation maximization (ML-EM) and ordered subsets expectation maximization (OSEM) slices of the object are obtained while three-dimensional (3D) reconstruction of the object is carried out using a modified marching cubes (MMC) algorithm. The spatial resolution of tomographic images obtained with the system was 2-3mm. The spatial resolution of a conventional system that uses filtered backprojection (FBP) for slices reconstruction was more than 9 mm.

Assessment of left ventricular stiffness and compliance.

Invasive and non-invasive methods exist to assess left ventricular compliance (LVC). This work has two parts, one experimental and one clinical. We estimated left chamber stiffness in dogs by using volume data from radionuclide ventriculography (RNV) and left ventricular pressure data, synchronized with a gating system to the intraventricular dp/dt max to obtain volume and pressure data from a mean cardiac cycle. In five dogs after acute experimental ischaemia, the modulus chamber stiffness Kp rose from 30.2 +/- 4.4 to 55.4 +/- 5.9 (P < 0.01). In 10 dogs with experimental infarction after intra-aortic balloon pumping, Kp decreased from 33.7 +/- 5.0 to 15.5 +/- 3.9 (P < 0.01) and in five dogs with experimental infarction, after intravenous infusion of sodium nitroprusside, Kp decreased from 41.4 +/- 5.5 to 22.2 +/- 2.8 (P < 0.01). In eight normal volunteers and in 20 postmyocardial infarction patients, we estimated a parameter reflecting the LVC by using volume data with blood flow velocity at the mitral valve annulus. Assuming that the mitral flow-velocity variation reflects LV pressure changes, the formula LVC = (dv/dt)/(dp-dt) becomes (dv/dt)/(df/dt) = dv/df. Values obtained in normals were 0.841 +/- 0.295 m-1s and after myocardial infarction 0.331 +/- 0.10 m-1s. Both methods allow clear separation in groups of animals or patients according to the expected changes in LVC or stiffness.

The breakdown of glycogen in the lysosomes of newborn rat hepatocytes: the effects of glucose, cyclic 3',5'-AMP and caffeine.

The effects of parenteral glucose, cyclic AMP and caffeine on the breakdown of glycogen in the lysosomes of newborn rat hepatocytes, were studied by using biochemical assays, electron microscopy and quantitative morphometry. Glucose prevented the normal postnatal increase in lysosomal volume, acid alpha 1,4 glucosidase activity and lysosomal glycogen breakdown. On the contrary, cyclic AMP and caffeine promoted this increase. There was a positive correlation between liver cyclic AMP concentration and acid glucosidase activity (R = 0.84, p < 0,001). Cyclic AMP also induced a change in the shape of lysosomes. The postulation that glucagon secreted after birth is the natural stimulus for the cyclic AMP-mediated postnatal increase in acid glucosidase activity and mobilization of the lysosomal glycogen in rat hepatocytes, is supported by these experimental findings.

A quantitative description of the insulin-induced ultrastructural changes in newborn rat hepatocytes.

The effects of insulin on the ultrastructure of newborn rat hepatocytes were systematically quantified at satisfactory statistical significance. Insulin prevented the normal postnatal increase in the total volume of lysosomes and the breakdown of glycogen inside these organelles. The lysosomal glycogen-hydrolysing enzyme, acid alpha 1,4 glucosidase was inhibited by the hormone. Insulin also prevented the normal postnatal increase in the total volume of peroxisomes, especially of the crystalloid core-devoid type. The hormone produced an increase in the area of cell membrane, due to the formation of many irregular folds of the cell surface. These results constitute good evidence for participation of lysosomes and peroxisomes in the overall glycogen degradation and or gluconeogenesis in the newborn rat hepatocytes.