Biomedical subjects

D Cavouras

Publications and source records attributed to D Cavouras.

At least 37 records · Page 2Linked to original sources

PubMed1997

A model for image formation and image quality prediction in diagnostic radiology.

A computer program modelling the formation of radiological images and predicting values of physical quantities that determine diagnostic image quality has been developed. The quantities are the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) associated with signal to noise ratio (SNR). The program is based on mathematical models that describe the effects of x-ray interactions with the imaged object and the image detector as well as phenomena concerning the optical signal propagation within the detector. All data on x-ray effects necessary for computer calculations were derived from published work whereas optical data were determined in our laboratory using experimental techniques. Model predictions were compared with direct quality measurements performed after image formation, on the image itself.

Computer Simulation↗

PubMed1997

Computer image analysis of ultrasound images for discriminating and grading liver parenchyma disease employing a hierarchical decision tree scheme and the multilayer perceptron neural network classifier.

Differential diagnosis of liver parenchyma disease and grading of the hepatic disease on ultrasound is a common radiological problem that influences patient management. The aim of this study was to apply image analysis methods on ultrasound images for discriminating liver cirrhosis from fatty liver infiltration and for grading hepatic disease, which is important in the management of the patients. Ultrasound images of histologically confirmed 18 livers with cirrhosis, 37 livers with fatty infiltration, and 24 normal livers of healthy volunteers were selected and were digitized for further computer processing. Twenty two textural features were calculated from small matrix samples selected from the ultrasound image matrix of the liver parenchyma. These features were used in the design a three level hierarchical decision tree classification scheme, employing the multilayer perceptron neural network classifier at each hierarchical tree level. At the first tree level, classification accuracy for distinguishing normal from abnormal livers was 93.7%, at the second level the accuracy for discriminating cirrhosis from fatty infiltration was 90.9%, and at the third level the accuracy in distinguishing between low and high grading liver cirrhosis or fatty infiltration was 94.1% and 84.9% respectively. The proposed computer software system may be of value to the radiologists in assessing liver parenchyma disease.

Decision Trees↗

PubMed1996

Developmental changes in the posterior cranial fossa of children studied by CT.

We reviewed 181 brain CT examinations, with no abnormal findings, to determine normative data for the posterior cranial fossa (PF) in children. The volume of the PF and the supratentorial cranial cavity (SC) was assessed by summing consecutive CT cross-sectional areas. Linear measurements of the PF structures-cerebellum, vermis, brain stem and fourth ventricle were also performed. The PF grows rapidly during the first 3 years of life and thereafter a smaller increase in size is observed. All the PF structures showed a positive correlation with the PF volume. The PF volume increased in parallel with that of the SC and the PF/SC volume ratio remained relatively constant during childhood. The establishment of normative data for the volume of the PF and its contents may be of value in the CT study of diseases associated with morphological alterations in the PF.

Adolescent↗

PubMed1996

X-ray induced luminescence and spatial resolution of La2O2S:Tb phosphor screens.

Absolute efficiency and modulation transfer function of laboratory prepared La2O2S:Tb phosphor screens of various coating thickness were studied. Detailed experimental data on the variation of absolute efficiency with x-ray tube voltage up to 200 kVp and screen coating thickness in transmission and reflection observation mode are given. Data were compared with similar results from other rare earth phosphor materials. Theoretical calculations were in good agreement with experimental data to permit estimation of intrinsic efficiency and coefficients related to light scattering and absorption within the phosphor material. The MTF of La2O2S:Tb screens was also experimentally and theoretically evaluated.

Dose-Response Relationship, Radiation↗

PubMed1996

Quantitative assessment of cerebral atrophy during and after treatment in children with acute lymphoblastic leukemia.

RATIONALE AND OBJECTIVES: The authors evaluate quantitatively brain atrophy induced by central nervous system prophylaxis in children treated for acute lymphoblastic leukemia during and after therapy completion. METHODS: Measurements of the width of the subarachnoid compartments were performed in 243 brain computed tomography (CT) examinations of 196 children examined during (125) and/or after (71) treatment for acute lymphoblastic leukemia without central nervous system involvement. Data were compared with normative data. RESULTS. Diffuse brain atrophy was observed in 74% and 65% of the CT examinations performed during and after cessation of treatment, respectively. The highest incidence of brain atrophy (78%) occurred during the administration of intrathecal chemotherapy. All children younger than 2 years of age exhibited brain atrophy. CONCLUSIONS: Brain atrophy is the principal CT finding in the majority of children treated for acute lymphoblastic leukemia and it can be attributed mainly to intrathecal chemotherapy. This finding can be observed long after therapy completion.

Adolescent↗

PubMed1996

An evaluation of the Y2O3:Eu3+ scintillator for application in medical x-ray detectors and image receptors.

The suitability off a Y2O3:Eu3+ scintillator for use in radiation detectors and medical image receptors was studied. Y2O3:Eu3+ was used in the form of laboratory prepared screens of different coating thicknesses. The x-ray luminescence efficiency of the screens was measured for tube voltages between 50-200 kVp and in both transmission and reflection modes of observation. The intrinsic x ray to light conversation efficiency (nc) and other parameters of the Y2O3:Eu3+ phosphor material related to optical scattering, absorption, and reflection were determined. These were used in the calculation of the image transfer characteristics, MTF and zero frequency DQE, for various screen coating thicknesses and x-ray tube voltages. The light emission spectrum of Y2O3:Eu3+ was measured (narrow band peak at 613 nm) and its spectral compatibility to the spectral sensitivity of several commonly employed optical photon detectors was determined. The x-ray luminescence efficiency varied with x-ray tube voltage, attaining maximum value at about 80 kVp for all screen thicknesses. It also varied with coating thickness reaching 25 microW m(-2)/mR s(-1) and 18 microW m(-2)/mR s(-1) at 175 mg/cm2 for reflection and transmission modes, respectively. The intrinsic x ray to light conversion efficiency and the image transfer characteristics were found to be comparable to several commercially used phosphors: nc = 0.095, MTF0.05 ranged between 10 and 25 line pairs per mm and peal values of DQE(0) varied between 0.33 and 0.14 in the coating thickness and kVp ranges useful for x-ray imaging. Spectral compatibility to some red sensitive optical photon detectors was excellent (0.9 or better). Results indicated that Y2O3:Eu3+ is a medium to high overall performance material that could be used in medical x-ray detectors and image receptors.

Biophysical Phenomena↗

PubMed1996

Study of subarachnoid spaces in children with idiopathic mental retardation.

The aim of this study was to assess quantitatively the size of the subarachnoid space in children with "idiopathic" mental retardation. The extent of various cerebrospinal fluid compartments was measured in 106 brain computed tomographic examinations of children with idiopathic mental retardation, and the results were compared with the corresponding normative data. The third ventricle was enlarged in 77% of the cases. A mild degree of diffuse widening of the subarachnoid spaces was found in about 30% of the patients. These morphologic alterations are additional observations supporting the hypothesis that "idiopathic" mental retardation has a biologic basis.

Adolescent↗

PubMed1995

The size of the intra- and extraventricular cerebrospinal fluid compartments in children with idiopathic benign widening of the frontal subarachnoid space.

The aim of this study was to quantify the intra- and extraventricular cerebrospinal fluid (CSF) spaces in children with benign enlargement of the frontal subarachnoid space (BE). The infra- and supratentorial CSF compartments were measured in 61 CT examinations of children with BE, 3-27 months old, and compared with those of 96 CT examinations considered normal. Measurements of the ventricular system, and the pontine and chiasmatic cisterns were related to cranial size. In all children with BE the lateral and third ventricles were dilated and the chiasmatic cistern was widened. The subarachnoid space was wider than the upper limits in the control group, in the frontal region (4 mm), and the anterior interhemispheric (4 mm) and Sylvian (3 mm) fissures. The infratentorial CSF compartments, the occipital subarachnoid space, the posterior part of the interhemispheric fissure and, in most cases, the cortical sulci were normal in size in children with BE. The majority were macrocephalic or had rapid head growth but there were also normocephalic children with normal head growth. The size of the posterior fossa was within the normal range in all children with BE. Idiopathic BE is not uncommon in children up to about 3 years old who are healthy or have minimal neurological disturbance and is characterised by a specific pattern of widening of the supratentorial CSF compartments.

Cephalometry↗

PubMed1994

CT evaluation of normal CSF spaces in children: relationship to age, gender and cranial size.

The extent of the cerebrospinal fluid (CSF) spaces was measured in 247 CT examinations, reported as normal, in children aged 3 months to 14 years. The measurements of the CSF compartments were divided by the sum of the transverse and longitudinal internal cranial diameters in the corresponding CT section, in order to take into account the size and shape of the growing skull. All CSF spaces were relatively larger in the younger (< or = 3 years) than in the older children, but did not differ between boys and girls, since the cranial size was taken into account. The CSF compartments increased in a non-uniform manner during the first 3 years of life, but after the age of four they developed uniformly and in parallel with the growing skull. Measurements of the subarachnoid spaces formed an age-related table, which may be of value when interpreting brain CT examinations of children.

Adolescent↗

PubMed1994

Renal parenchymal thickness in children measured by computed tomography.

Renal parenchymal thickness was measured at different regions and levels through the kidney in 162 abdominal computed tomography (CT) examinations of children 5 months to 14 years old. The transverse diameter of the first lumbar vertebra (L1) was also measured, in order to take into account the child's body habitus. All patients were examined with an indication other than renal disease and had no abnormal CT findings in the retroperitoneum. Renal parenchyma increased in parallel with the transverse diameter of L1 and did not depend on age or sex in children of the same body format. There were no significant differences in size between the right and the left kidneys. Renal measurements were tabulated on reference tables, as an aid in the assessment of renal parenchymal thickness in children undergoing abdominal CT examination.

Adolescent↗

PubMed1994

CT assessment of normal splenic size in children.

The size of the normal spleen was estimated by CT in 153 children examined with indication unrelated to splenic disease. In each patient the width, thickness, length and volume of the spleen were calculated. Measurements were also normalized to the transverse diameter of the body of the first lumbar vertebra. The spleen underwent significant growth during the first 4 years of life and reached maximum size at the age of 13. There was no differences in splenic volume between boys and girls. Splenic thickness correlated best with normal splenic volume. The strongest correlation was also found between splenic thickness and volume in a group of 45 children with clinically evident splenomegaly. Splenic thickness, an easy-to-use measurement, may be employed in everyday practice to represent splenic volume on CT.

Adolescent↗

PubMed1993

Pre- and post-nephrectomy kidney enlargement in patients with contralateral renal cancer.

Pre- and post-nephrectomy kidney growth was studied by computed tomography (CT) in 32 patients with contralateral renal cancer. Kidney enlargement was assessed by comparing the size of the unaffected kidney, in 32 pre- and 61 post-nephrectomy CT examinations, with the corresponding normal size, determined from 120 CT examinations of binephric individuals with no renal disease. The unaffected kidney was found to be 36% larger 1 month before nephrectomy and 54, 62 and 47% in the 1st, 2nd, and 3rd postoperative year, respectively. Compensatory renal growth was influenced both by contralateral cancer and nephrectomy and did not depend on the patient's age or sex.

Adult↗

PubMed1992

CT evaluation of compensatory renal growth in relation to postnephrectomy time.

In 27 patients nephrectomized for renal carcinoma, the compensatory hypertrophy of the remaining kidney was assessed by 72 CT examinations performed one month before and during 32 months after nephrectomy. Kidney size was estimated on CT by multiple measurements of the renal parenchymal thickness. Kidney growth was evaluated by comparing the amount of renal parenchyma before and after contralateral nephrectomy. Renal compensatory hypertrophy varied with postnephrectomy time. Kidney enlargement was 15% in the first 3 months, reached maximum 30% about a year later, and was reduced to 5%, 2 1/2 years postoperatively.

Adult↗

PubMed1990

The thickness of the renal parenchyma decreases with age: a CT study of 360 patients.

Renal parenchymal thickness was estimated by using CT in 360 patients with no evidence of renal disease. In each patient, the measurements were normalized to the transverse diameter of the vertebral body and a reference table was formulated. The renal parenchymal thickness decreases about 10% per decade of increasing age in both men and women. These findings are consistent with previously reported findings based on autopsy material. The proposed table may be useful as a criterion for assessing normal renal parenchyma on CT.

Adult↗

PubMedDate not supplied

Interposition of the colon between the kidney and the psoas muscle: a normal anatomic variation studied by CT.

The position of the bowel in the pararenal space was examined in relation to the kidney and the psoas muscle in 1203 abdominal computed tomographic (CT) examinations. The ascending colon was found between the lower kidney pole and the psoas muscle in 1.7% and the descending colon in 0.7% of the patients. This variation appeared more frequently in women, young adults, and individuals with less intrabdominal fat. Lateral displacement of the lower kidney pole was observed in 40% of the patients with this normal variation. These findings may be of value when interpreting urographic and abdominal CT examinations.

Adult↗

PubMedDate not supplied

A study of the variation of colonic positioning in the pararenal space as shown by computed tomography.

In a review of 1708 consecutive CT examinations of the abdomen the position of the ascending and descending colon in relation to the posterior and lateral edge of the kidney was studied. It was found that part of the colon was positioned posterior or posterolateral to the kidney's edge in percentages that varied between 14.2% and 0.9% in the different sex groups at the levels of upper, mid- and lower poles of the right and left kidney. It is concluded that this anatomical variation should be known if colon perforation is to be avoided during percutaneous nephrostomy or biopsy.

Adult↗

PubMedDate not supplied

Image analysis methods for solitary pulmonary nodule characterization by computed tomography.

Computer software was designed for classifying solitary pulmonary nodules (SPNs) into benign and malignant from their CT images, using image analysis methods. The system made use of three features, computed from the CT density matrix of the SPN, and a class-discriminating algorithm. System evaluation was performed on 51 histologically confirmed SPNs of indeterminate CT diagnosis. Overall classification accuracy in distinguishing benign and malignant SPNs was 90.2%, while 83.3% of the benign and 93.9% of the malignant SPNs were correctly classified. The proposed system may be of value to the radiologist in assessing the probability of malignancy in patients with a solitary pulmonary nodule.

Adult↗

PubMedDate not supplied

Computer-based grading of haematoxylin-eosin stained tissue sections of urinary bladder carcinomas.

PURPOSE: A computer-based image analysis system was developed for assessing the malignancy of urinary bladder carcinomas in a more objective manner. Tumours characterized in accordance with the WHO grading system were classified into low-risk (grades I and II) and high-risk (grades III and IV). MATERIALS AND METHODS: Images from 92 haematoxylin-eosin stained sections of urinary bladder carcinomas were digitized and analysed. An adequate number of nuclei were segmented from each image for morphologic and textural analysis. Image segmentation was performed by an efficient algorithm, which used pattern recognition methods to automatically characterize image pixels as nucleus or background. Image classification into low-risk or high-risk tumours was performed by means of the quadratic non-linear Bayesian classifier, which was designed employing 36 textural and morphological features of the nucleus. RESULTS: Automatic segmentation of nuclei on all images was about 90% on average. Overall system accuracy in correctly classifying tumours into low-risk or high-risk was 88%, employing the leave-one-out method and the best combination of three textural and one morphological feature. Classification accuracy for low-risk tumours was 88.8% and for high-risk tumours 86.2%. CONCLUSION: The proposed image analysis system may be of value to the objective assessment of the malignancy of urine bladder carcinomas, since it relies on nuclear parameters that are employed in visual grading and their prognostic value has been proved.

Algorithms↗