Beta voxel S values for internal emitter dosimetry.

Monte Carlo volume integration of dose point kernels was used for calculating voxel S values of beta emissions of radionuclides of interest for internal radiotherapy. The method was verified by comparing our results with others derived from Monte Carlo radiation transport simulation. The algorithm has been implemented in a C++ program that can be used by any laboratory to calculate voxel S values of beta emissions from tabulated dose point kernels and for any combination of pixel edges and the thickness of SPECT and PET images without the complexity and expertise needed for direct Monte Carlo radiation transport simulations.

A multiresolution restoration method for cardiac SPECT imaging.

In this study we present a multiresolution based method for restoring cardiac SPECT projections. Original projections were decomposed into a set of sub-band frequency images by using analyzing functions localized in both the space and frequency domain. This representation allows a simple denoising and restoration procedure by discarding high-frequency channels and performing inversion only in low frequencies. The method was evaluated in bull's eye reconstructions of a realistic cardiac chest phantom with a custom-made liver insert and 99mTc liver-to-heart activity ratios (LHAR) of 0:1, 1.5:1, 2.5:1, and 3.5:1. The cardiac phantom in free air was used as the reference standard. Reconstructions were performed by filtered backprojection using (1) no correction; (2) restoration without attenuation correction; (3) attenuation correction without restoration; and (4) restoration and attenuation correction. The attenuation correction was carried out with the Chang's method for one iteration. Results were compared with those obtained using an optimized prereconstruction Metz filter. Quantitative analysis was performed by calculating the normalized chi-square measure and mean +/- s.d. of bull's eye counts. In reconstructions with high liver activity (LHAR > 2), attenuation correction without restoration severely distorted the polar maps due to the spill-over of liver activity into the inferior myocardial wall. Both restoration methods when combined with an attenuation correction compensated this artifact and yielded uniform polar maps similar to that of the standard reference. There was no visual or quantitative difference between the performance of Metz filtering and multiresolution restoration. However, the main advantage of the multiresolution method is that it states a more concise and straightforward approach to the restoration problem. Multiresolution based methods does not require information about the object image or optimization processes, such as in conventional nuclear medicine restoration filters. In addition, the method is easy to implement using DFT techniques and potentially can be extended to noniterative spatially shift-invariant restorations in SPECT.

Tecnica de la ventriculografia nuclear. Su valor en cardiopatia isquemica. / Technique of the nuclear ventriculography. Its value in ischemic cardiopathy

Las tecnicas nucleares que emplean camara gamma y computadora digital, han cobrado especial interes en cardiologia durante los ultimos anos.Estos procedimientos presentan como principales ventajas su simplicidad y caracter no invasivo, asi como la informacion que permiten disponer.En el trabajo se presenta la tecnica de ventriculografia nuclear empleada en el laboratorio de los autores y los resultados obtenidos en un grupo de sujetos normales y pacientes con cardiopatia isquemica. Los parametros que se calculan son: fracciones de ejeccion y velocidades de llenado y vaciamiento para cada ventriculo. Ademas se determina el retardo de la contraccion de un ventriculo respecto al otro. El movimiento de paredes se estudia por medio de las imagenes de fase y amplitud, obtenidas al aplicar el aparato matematico de la transformada de Fourier a la ventriculografia nuclear. Estas imagenes diferencian zonas normokineticas de aquinesias e hipoquinesias regionales y permiten identificar segmentos con movimiento paradojico.Los resultados obtenidos con la ventriculografia izquierda y coronariografia en 15 sujetos. Se concluye en la utilidad y valor de la ventriculografia nuclear en una serie de situaciones clinicas

Hemodynamic effects of atenolol in labile hypertension.

The hemodynamic effects provoked by 15 days treatment with atenolol 100 mg/day in a single oral dose were studied in labile hypertensive patients. Radiocardiography with 131IRHISA was employed in order to calculate: Cardiac output and index (CO, CI); stroke volume and index (SV, SI), total blood volume and index (TBV, TBVI) and total peripheral resistance (TPR). Atenolol caused a significant reduction in arterial pressure, heart rate, CO and CI (p less than 0.001). The drug also reduced TBV (11%) and TBVI (16%) from controls: however, these changes were not significant. A direct relationship was found between CO with heart rate (r = 0.79, p less than 0.01), and between CO with TBV (r = 0.82, p less than 0.01); also an inverse relationship was found between TBV with TPR (r = 0.874, p less than 0.01). These relationships lost significance during treatment with the drug. The lowering of cardiac output contributes to the anti-hypertensive effect of atenolol, but although the reduction in blood volume was not significant it is possible that this also may be a factor.

A computerized method of quantitative analysis of ventricular phase distributions.

Phase images from gated equilibrium cardiac studies, were analysed quantitatively by a computerized automatic method. The study included 17 normal subjects and 33 patients with an acute myocardial infarction (AMI). Phase histograms were constructed for each ventricle and their peaks were identified by a convolution algorithm for smoothing and differentiation. Intra- and interventricular phase shifts as well as the percentage of normal contracting pixels (NCP) were calculated. The results showed that the left ventricular ejection fraction (LVEF) tends to decrease when the intraventricular phase shift increases. Interventricular phase shifts out of the normal range (+/- 10 degrees) were observed predominantly in patients with an extensive anterior or anteroseptal AMI. The closest relationship was found between LVEF and the percentage of NCP. This parameter decreases when akinetic and dyskinetic areas increase and could be considered as a quantitative index of the synchronism in myocardial contraction useful in the prognosis and follow-up of patients.

Measurement of right and left ventricular ejection fractions by gated equilibrium scintigraphy using Fourier functional images.

Left and right ventricular ejection fractions (LVEF and RVEF) were calculated by gated equilibrium scintigraphy in 28 normal controls and in 21 patients with heart disease. Regions of interest (ROIs) for the ventricles were assigned on the amplitude and phase Fourier images. Two methods of preprocessing of data were compared. In Method 1 the resolution was improved and the statistical noise was reduced, while in Method 2 only the statistical noise was reduced. There were no differences between the results of the two methods for the left ventricle. The mean LVEF for normal subjects was 0.63 +/- 0.06. For the right ventricle, Method 1 showed higher sensitivity in detecting reduced RVEF in pathological situations. The mean RVEF by Method 1 for normal controls was 0.56 +/- 0.07, which is significantly different (p less than 0.001) than that found by Method 2 (0.36 +/- 0.05), and similar to those reported by others employing the firstpass method. The results show the usefulness of the phase Fourier image and the importance of a suitable preprocessing of data for determining RVEF by gated equilibrium scintigraphy.