Search PubMed⌕ Search

Biomedical subjects

H Benali

Publications and source records attributed to H Benali.

31 records · Page 2Linked to original sources
PubMed1995

A new correction method for gamma camera non-uniformity due to energy response variability.

We present a new uniformity correction (Fourier energy correction) which is designed to correct for gamma camera non-uniformity caused by variations of the energy response function within a wide spectral range. A convolution model is used to describe the spatial distortions of the energy response function. The model is solved in Fourier space. A preliminary flood acquisition is required to obtain energy-dependent Fourier weights which are used to correct subsequent acquisitions. The influence of the parameters involved in the correction procedure is studied and the Fourier energy correction is compared to a conventional multiplicative energy correction for different acquisition geometries. The Fourier energy correction appears especially useful when the energy information associated with each detected photon is analysed using a fine sampling, or when windows different from the photopeak window are used.

Biophysical Phenomena↗
PubMed1995

A fractal approach to the segmentation of microcalcifications in digital mammograms.

This paper presents a computerized method for the automated segmentation of individual microcalcifications in a region of interest (ROI) known to contain a cluster in digital mammograms. Mammographic parenchyma caj be accurately modeled with the fractal approach, but not areas with microcalcifications. The digitized image is divided into 16 x 16-pixel overlapping windows and those accurately modeled by the fractal model are eliminated. The next steps include local thresholding of the ROIs using an iterative method, the elimination of some of the artifacts and identification of the clustered microcalcifications using a clustering algorithm. The evaluation was performed on 81 simulated clusters superimposed on normal mammographic backgrounds and on a representative database of 408 real mammograms. Microcalcification locations were identified by two radiologists independently. These locations were compared to those found by the computer algorithm. An average of 59% of the simulated microcalcifications and 69% of the microcalcifications common to both radiologists were detected. The algorithm described provides a fully automated method for the segmentation of individual microcalcifications in an area of the mammogram known to contain a cluster.

Biopsy↗
PubMed1995

Comparative assessment of nine scatter correction methods based on spectral analysis using Monte Carlo simulations.

UNLABELLED: We compared nine scatter correction methods based on spectral analysis which process SPECT projections. METHODS: Monte Carlo simulation was used to generate histories of photons emitted from a realistic 99mTc phantom. A particular projection was considered. Information regarding the history, location and energy of the photons detected in this projection was analyzed to test the assumptions underlying each scatter correction method. Relative and absolute quantification and signal-to-noise ratio were assessed for each scatter corrected image. RESULTS: For the simulated data, two methods do not enable activity quantification. Among the methods requiring some parameters to be calibrated, the dual-energy window method shows the best compromise between accuracy and ease of implementation but introduces a bias in relative quantification. In this respect, a triple-energy window technique is more accurate than the dual-window method. A factor analysis approach results in more stable quantitative accuracy (error approximately 10%) for a wide range of activity but requires a more sophisticated acquisition mode (30 energy windows). CONCLUSION: These results show that a scatter correction method using spectral analysis can be used to substantially improve accurate quantification.

Humans↗
PubMed1994

A comparative study of scatter correction methods for scintigraphic images.

Phantom studies have demonstrated that factor analysis of medical image sequences using target apex-seeking (FAMIS-TAS) applied to spectral scintigraphic image sequences is an efficient adaptive scatter correction method. We assessed the improvement in quality of clinical images using FAMIS-TAS as compared with two other scatter correction techniques: conventional 20% photopeak window (PW) and scatter window subtraction (SWS). Thirty normal technetium-99m hydroxymethylene diphosphonate bone scans were processed. Bone to soft tissue contrasts and signal-to-noise and contrast-to-noise ratios were measured. The overall image quality was evaluated using an observer testing questionnaire submitted to four physicians. Quantitative parameters showed that FAMIS-TAS images displayed the best bone to soft tissue contrasts and contrast-to-noise ratios, but the lowest signal-to-noise ratios. PW images presented the lowest contrasts and contrast-to-noise ratios, and the highest signal-to-noise ratios. SWS gave intermediate results. According to the observer testing results, PW images showed the lowest bone to soft tissue contrasts and the highest signal-to-noise ratios. FAMIS-TAS images showed the lowest signal-to-noise ratios. The images processed by the three methods displayed the same anatomical information.

Adolescent↗
PubMed1994

Scatter correction in scintigraphy: the state of the art.

In scintigraphy, the detection of scattered photons degrades both visual image analysis and quantitative accuracy. Many methods have been proposed and are still under investigation to cope with scattered photons. The main features of the problem of scattering in radionuclide imaging are presented first, to provide a sound foundation for a critical review of the existing scatter correction techniques. These are described using a classification relating to their aims and principles. Their theoretical potentials are analysed, as well as the difficulties of their practical implementation. Finally, the problems of their evaluation and comparison are discussed.

Humans↗
PubMed1994

A simulation model of clustered breast microcalcifications.

A simulation model of clustered microcalcifications superimposed on normal mammographic backgrounds has been developed and evaluated. A cluster is described according to its size, the number of microcalcifications it contains, and their density. A microcalcification is defined on the basis of its size, shape, location within the cluster, its contrast, and the distribution of the gray-level values between pixels that belong to it. Gray-level parameters are dependent on the surrounding tissue, which is also slightly modified. The main dependencies between the parameters are taken into account. All the parameters are randomly sampled using distribution laws determined from the statistical analysis of 408 real clusters containing a total of 8611 microcalcifications. Some statistical characteristics depend on the structural mammographic pattern on which the cluster is superimposed. The evaluation of the simulation model, performed by two radiologists on a test set of 100 real and simulated clusters, did not reveal any statistically significant difference between the simulated clusters and the real ones. This method provides clusters of microcalcifications with well-defined characteristics and can be used to evaluate the accuracy of computerized detection methods.

Biophysical Phenomena↗
PubMed1993

Usefulness of technetium-99m hydroxymethylene diphosphonate scans in localizing bone metastases of differentiated thyroid carcinoma.

Iodine-131 is uniquely able to demonstrate iodine uptake of differentiated thyroid carcinoma (DTC), but precise localization may be difficult, especially in the thorax, due to the quality of image resolution with 131I and the lack of anatomical landmarks. When bone metastases do not show radioiodine uptake bone scintigraphy can be used to detect them. We studied two groups of patients. In group 1, 15 patients with known bone metastases of DTC were treated with 3.7 GBq 131I. After 4 or 5 days, technetium-99m hydroxymethylene diphosphonate (HMDP; 740 MBq) was injected and a whole-body scan with simultaneous acquisition of 131I and 99mTc-HMDP images was carried out using a large field of view gamma camera fitted with a high-energy collimator. Technetium uptake was abnormal in 47 of 63 localizations, being increased in 29 foci, decreased in 7 and heterogeneous in 11. The superimposition of 131I and 99mTc-HMDP scans permitted an accurate localization in 80% of spine metastases and in 46% of osseous thoracic localizations, even in the presence of lung metastases. In group 2, 9 patients, who had bone pain, neurological signs or elevated serum thyroglobulin, had DTC bone metastases without iodine uptake. They received a diagnostic dose of 99mTc-HMDP 3h prior to scintigraphy with a large field of view gamma camera fitted with a low-energy collimator. Technetium uptake was abnormal in 37 of 38 localizations, being increased in 34 foci and decreased in 3. One false-negative was found in a skull metastasis. In both groups of patients, 99mTc-HMDP scans were useful.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenocarcinoma, Follicular↗
PubMed1993

Target apex-seeking in factor analysis of medical image sequences.

The aim of factor analysis of medical image sequences (FAMIS) is to estimate a limited number of physical or physiological fundamental functions. Its oblique rotation stage strongly affects the quality and the interpretation of the resulting estimates (factors and factor images). A new target apex-seeking method which integrates physical or physiological knowledge in this stage is described. This knowledge concerns some of the fundamental functions and reacts on the determination of all the factors. A simulated spectral study illustrates the method. We discuss its properties in comparison with the other approaches using a priori physical or physiological information.

Computer Simulation↗
PubMed1993

A statistical model for the determination of the optimal metric in factor analysis of medical image sequences (FAMIS).

A statistical model is added to the conventional physical model underlying factor analysis of medical image sequences (FAMIS). It allows a derivation of the optimal metric to be used for the orthogonal decomposition involved in FAMIS. The oblique analysis of FAMIS is extended to take this optimal metric into account. The case of scintigraphic image sequences is used. We derive in this case that the optimal decomposition is obtained by correspondence analysis. A scintigraphic dynamic study illustrates the practical consequences of the use of the optimal metric in FAMIS.

Factor Analysis, Statistical↗
PubMedDate not supplied

Extraction of functional volumes from medical dynamic volumetric data sets.

A method based on factor analysis is presented to process dynamic volumetric (t + 3D) data sets acquired for flow, excretion, or metabolic studies. It estimates a reduced number of underlying physiological kinetics and their associated spatial distributions, corresponding to functional volumes, using dedicated algorithms. The global (t + 3D) approach is shown to be superior to the conventional one, which repeats estimations on each (t + 2D) data set, obtained for each slice or projection of the volume.

Algorithms↗