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J Sau

Publications and source records attributed to J Sau.

9 recordsLinked to original sources
PubMed2000

A constrained Gauss-Seidel method for correction of point spread function effect in MR spectroscopic imaging.

Magnetic resonance spectroscopic imaging is limited by a low signal-to-noise ratio, so a compromise between spatial resolution and examination time is needed in clinical application. The reconstruction of truncated signal introduces a Point Spread Function that considerably affects the spatial resolution. In order to reduce spatial contamination, three methods, applied after Fourier transform image reconstruction, based on deconvolution or iterative techniques are tested to decrease Point Spread Function contamination. A Gauss-Seidel (GS) algorithm is used for iterative techniques with and without a non-negative constraint (GS+). Convergence and noise dependence studies of the GS algorithm have been done. The linear property of contamination was validated on a point sample phantom. A significant decrease of contamination without broadening the spatial resolution was obtained with GS+ method compared to a conventional apodization. This post-processing method can provide a contrast enhancement of clinical spectroscopic images without changes in acquisition time.

Algorithms↗
PubMed2000

Streak artifact reduction in filtered backprojection using a level line-based interpolation method.

UNLABELLED: Because of the limited number of projections, the mathematic reconstruction formula of the filtered backprojection (FBP) algorithm may create an artifact that streaks reconstructed images. This artifact can be imperfectly removed by replacing the ramp filter of the FBP with an ad hoc low-pass filter, the cost being the loss of contrast and definition. In this study, a solution was proposed to increase, by computational means, the number of projections to reduce the artifact at a lower cost. The cost was a postacquisition process, which was reasonably time consuming. METHODS: The process was called interpolation of projections by contouring (IPC). First, level lines were plotted on the sinogram to delimit isocount regions; then, the regions containing the interpolated points were found, and to each point was assigned the intensity of its isocount region. Using this process, the data could be resampled, allowing an increase in the number of projections or the number of pixels by projections. A phantom study of bone scintigraphy was performed to compare the slices obtained with and without the IPC process with the true image. A clinical case was also presented. RESULTS: The phantom study showed that with the IPC process, the reconstructed slice was closer to the model, inside and outside the body, when the sinogram was resampled to multiply by 2 or 3 the number of projections, with the same number of pixels per projection. In the clinical study, the streak artifact was reduced, especially outside the body, although only a ramp filter was used. CONCLUSION: The IPC process succeeded in reducing the streak artifact. This process did not require any modification in acquisition and was not operator dependent. The increase in the number of projections is likely a necessary but not a sufficient condition to reduce the streak artifact: if not corrected, the attenuation could be a limiting factor in the removal of this artifact when the number of projections increases.

Algorithms↗
PubMed1999

A model of the dual effect of gadopentetate dimeglumine on dynamic brain MR images.

An optimized dynamic gradient echo sequence with two echoes is used to obtain data that can be analyzed with indicator dilution theory as well as with pharmacokinetic theory. Taking advantage of the simultaneity of T(*)(2) and T(1) information, both theories can be employed and merged to interpret consistently the observed effects of the redistribution of a contrast agent (gadopentetate dimeglumine) into the tissue from first pass onward. The regional cerebral blood volume (rCBV) and the exchange rate of the contrast agent between the vascular and the interstitial space through the blood-brain barrier are analyzed for each pixel in a two-step algorithm. Two values for rCBV are obtained with different weighting for the microvascular fraction of the blood volume. Because the analysis, called PELEAKAN, is capable of separating effects related to perfusion (through intravascular blood volume) and to leakage in places where the blood-brain barrier is damaged, it is an appropriate tool for evaluating these parameters in brain tumors, and we show clinical examples of this analysis in brain tumor patients.

Adult↗
PubMed1999

Assessment of osteosarcoma response to neoadjuvant chemotherapy: comparative usefulness of dynamic gadolinium-enhanced spin-echo magnetic resonance imaging and technetium-99m skeletal angioscintigraphy.

The aim of this work was to study and compare the usefulness of dynamic contrast-enhanced spin-echo MR imaging with high temporal resolution hydroxymethylene diphosphonate technetium-99 m skeletal angioscintigraphy in predicting the osteosarcoma histological response to neoadjuvant chemotherapy. Twelve patients with resectable osteosarcoma were prospectively monitored with dynamic MR imaging and skeletal scintigraphy before start of neoadjuvant chemotherapy, after two cycles of therapy and before surgery. Neoplasm signal intensity and activity intensity were plotted against time, and slopes were calculated for percentage increase over baseline values in the first minute. Stability and increase in slope values during or after chemotherapy were defined as a "radiological non-response". Changes in slopes were compared with the "histological response" (Huvos grading). At midpoint of the chemotherapy, these two imaging modalities failed in predicting final histological response. After the completion of the chemotherapy, these imaging modalities allowed the prediction of histological response with the same accuracy (91 %). In this series, dynamic MR imaging and technetium skeletal scintigraphy provide similar results regarding the prediction of final histological response during neoadjuvant chemotherapy; these results cannot be used to modify the therapeutic protocol at midpoint of chemotherapy; these imaging tools predict accurately the histological response at the end of chemotherapy. These latter results may permit anticipation of the adjuvant chemotherapy strategy during decalcification procedures in resected osteosarcoma and thus to monitor chemotherapy in non-surgical osteosarcoma.

Adolescent↗
PubMed1999

Noise removal using factor analysis of dynamic structures: application to cardiac gated studies.

UNLABELLED: Factor analysis of dynamic structures (FADS) facilitates the extraction of relevant data, usually with physiologic meaning, from a dynamic set of images. The result of this process is a set of factor images and curves plus some residual activity. The set of factor images and curves can be used to retrieve the original data with reduced noise using an inverse factor analysis process (iFADS). This improvement in image quality is expected because the inverse process does not use the residual activity, assumed to be made of noise. The goal of this work is to quantitate and assess the efficiency of this method on gated cardiac images. METHODS: A computer simulation of a planar cardiac gated study was performed. The simulated images were added with noise and processed by the FADS-iFADS program. The signal-to-noise ratios (SNRs) were compared between original and processed data. Planar gated cardiac studies from 10 patients were tested. The data processed by FADS-iFADS were subtracted to the original data. The result of the substraction was studied to evaluate its noisy nature. RESULTS: The SNR is about five times greater after the FADS-iFADS process. The difference between original and processed data is noise only, i.e., processed data equals original data minus some white noise. CONCLUSION: The FADS-iFADS process is successful in the removal of an important part of the noise and therefore is a tool to improve the image quality of cardiac images. This tool does not decrease the spatial resolution (compared with smoothing filters) and does not lose details (compared with frequential filters). Once the number of factors is chosen, this method is not operator dependent.

Computer Simulation↗
PubMed1998

Regional cerebral blood flow determination using 133Xe and a standard rotating gamma-camera.

While most of the methods for quantitative regional cerebral blood flow (rCBF) determination in man requires expensive fast devices, a method is proposed using single photon emission computed tomography with a conventional rotating gamma camera and 133Xe inhalation. It is tested using a computer simulation of a cerebral exam and a simplified CBF map as a model. The results obtained show that this method is relevant and can be tested in clinical studies.

Blood Flow Velocity↗
PubMed1996

Automated detection of the left ventricular region in gated nuclear cardiac imaging.

An approach to automated outlining the left ventricular contour and its bounded area in gated isotopic ventriculography is proposed. Its purpose is to determine the ejection fraction (EF), an important parameter for measuring cardiac function. The method uses a modified version of the fuzzy C-means (MFCM) algorithm and a labeling technique. The MFCM algorithm is applied to the end diastolic (ED) frame and then the (FCM) is applied to the remaining images in a "box" of interest. The MFCM generates a number of fuzzy clusters. Each cluster is a substructure of the heart (left ventricle,...). A cluster validity index to estimate the optimum clusters number present in image data point is used. This index takes account of the homogeneity in each cluster and is connected to the geometrical property of data set. The labeling is only performed to achieve the detection process in the ED frame. Since the left ventricle (LV) cluster has the greatest area of the cardiac images sequence in ED phase, a framing operation is performed to obtain, automatically, the "box" enclosing the LV cluster. THe EF assessed in 50 patients by the proposed method and a semi-automatic one, routinely used, are presented. A good correlation between the two methods EF values is obtained (R = 0.93). The LV contour found has been judged very satisfactory by a team of trained clinicians.

Algorithms↗