Biomedical subjects

Didier Bielen

Publications and source records attributed to Didier Bielen.

9 recordsLinked to original sources

PubMed2006

Computer-aided detection of colonic polyps using low-dose CT acquisitions.

RATIONALE AND OBJECTIVES: This report proposes an alternative method for the automatic detection of colonic polyps that is robust enough to be directly applicable on low-dose computed tomographic data. MATERIALS AND METHODS: The polyp modeling process takes into account both the gray-level appearance of polyps (intensity profiles) and their geometry (extended Gaussian images). Spherical harmonic decompositions are used for comparison purposes, allowing fast estimation of the similarity between a candidate and a set of previously computed models. Starting from the original raw data (acquired at 55 mA), five patient data sets (prone and supine scans) are reconstructed at different dose levels (to 5 mA) by using different kernel filters, slice overlaps, and increments. Additionally, the efficacy of applying an edge-preserving smoothing filter before detection is assessed. RESULTS: Although image quality decreases when decreasing acquisition milliamperes, all polyps greater than 6 mm are detected successfully, even at 15 mA. Although not important at high doses, smoothing improves detection results for ultra-low-dose (tube current<15 mA) data. CONCLUSION: The advantage of low-dose scans is a significant decrease in effective dose from 4.93 to 1.61 mSv while retaining high detection values, particularly important when thinking of population screening.

Algorithms↗

PubMed2005

Computer aided detection for low-dose CT colonography.

The paper describes a method for automatic detection of colonic polyps, robust enough to be directly applied to low-dose CT colonographic datasets. Polyps are modeled using gray level intensity profiles and extended Gaussian images. Spherical harmonic decompositions ensure an easy comparison between a polyp candidate and a set of polypoid models, found in a previously built database. The detection sensitivity and specificity values are evaluated at different dose levels. Starting from the original raw-data (acquired at 55mAs), 5 patient datasets (prone and supine scans) are reconstructed at different dose levels (down to 5mAs), using different kernel filters and slice increments. Although the image quality decreases when lowering the acquisition mAs, all polyps above 6mm are successfully detected even at 15 mAs. Accordingly the effective dose can be reduced from 4.93mSv to 1.61 mSv, without affecting detection capabilities, particularly important when thinking of population screening.

Algorithms↗

PubMed2005

Translumbar thrombin embolization of an aortic pseudoaneurysm complicating lumbar disk surgery.

We report a case of translumbar embolization of an aortic pseudoaneurysm complicating lumbar disk surgery. The iatrogenic pseudoaneurysm was initially treated by open repair, but due to failure of this treatment, we opted for direct translumbar thrombin injection under computed tomography (CT) guidance. The patient recovered completely, and follow-up CT scans showed progressive shrinkage of the residual retroperitoneal hematoma. This minimally invasive treatment should be considered in selected cases as a valuable treatment option for pseudoaneurysms that arise from the aorta.

Aneurysm, False↗

PubMed2004

Dynamic contrast-enhanced MRI of the pancreas: initial results in healthy volunteers and patients with chronic pancreatitis.

PURPOSE: To characterize pancreatic perfusion in volunteers and patients with chronic pancreatitis (CP) by dynamic contrast-enhanced (DCE) MRI. MATERIALS AND METHODS: Pancreatic enhancement after bolus injection of Gd-DTPA with a three-dimensional ultrafast partial-Fourier radiofrequency (RF) spoiled gradient-echo (GE) acquisition was examined prospectively. An acquisition volume of the pancreatic parenchyma was obtained every 4.2 seconds during a single breath-hold in 31 volunteers and 19 patients with CP. We calculated the wash-in rate and a newly defined parameter, the "time-to-inflow deceleration" (TID). A statistical analysis of the differences between both groups was performed with the use of Student's t-test. RESULTS: Significant differences in the TID and wash-in rate were found for the head and body of the pancreas: the TID was 22.4 sec +/- 4.4 sec and 23.5 sec +/- 6.1 sec in the pancreatic head and body of the healthy volunteers, and 29.8 sec +/- 8.6 sec and 29.4 sec +/- 3.8 sec in patients with CP. The wash-in rate was 96 +/- 37 sec(-1) and 101 +/- 27 sec(-1) in controls, and 62 +/- 17 sec(-1) and 75 +/- 27 sec(-1) in CP. CONCLUSION: CP can be identified by semiquantitative changes on DCE-MRI. Whether DCE-MRI of the pancreas can be used to detect early CP remains to be validated.

Adult↗

PubMed2003

Respiration-induced movement of the upper abdominal organs: a pitfall for the three-dimensional conformal radiation treatment of pancreatic cancer.

Respiration-induced movement of the upper abdominal organs (pancreas, liver and kidneys) was assessed in 12 subjects using dynamic magnetic resonance imaging. The movement of each organ in the cranio-caudal, the lateral and the anterior-posterior direction was deduced from the movement of the center of gravity on two-dimensional images. This center of gravity was computed from the volume delineated on sequential 8-mm slices of both sagittal and coronal dynamic series. The largest movements were noticed in the cranio-caudal direction for pancreas and liver (23.7+/-15.9 mm and 24.4+/-16.4 mm). The kidneys showed smaller movements in the cranio-caudal direction (left kidney 16.9+/-6.7 mm and right kidney 16.1+/-7.9 mm). The movements of the different organs in the anterior-posterior and lateral directions were less pronounced. It is of the greatest importance to be aware of these movements in the planning of a conformal radiation treatment for pancreatic cancer.

Humans↗

PubMed2003

Magnetic resonance imaging of the effects of infliximab on perianal fistulizing Crohn's disease.

OBJECTIVES: Although the clinical efficacy of infliximab as measured by closure of fistulas in Crohn's disease has been demonstrated, its influence on the inflammatory changes in the fistula tracks is less clear. The aim of the present study was to assess the behavior of perianal fistulas before and after infliximab treatment. METHODS: Magnetic resonance imaging (MRI) and clinical evaluation were performed in a total of 18 patients before and after treatment with infliximab. An MRI-based score of perianal Crohn's disease severity was developed using both criteria of local extension of fistulas (complexity, supralavetoric extension, relation to the sphincters and of active inflammation (T2 hyperintensity, presence of cavities/abscesses, and rectal wall involvement). RESULTS: The MRI score was reliable in assessing the fistula tracks, with a good interobserver concordance (p < 0.001). Fistula tracks with signs of active inflammation were found in all 18 patients at baseline and collections in seven. After short-term infliximab treatment, active tracks persisted in eight of 11 patients who had clinically responded to infliximab. After long-term (46 wk) infliximab therapy, MRI signs of active track inflammation had resolved in three of six patients. CONCLUSIONS: We have developed an MRI-based score of perianal Crohn's disease severity to assess the anatomical evolution of Crohn's fistulas. Our study demonstrates that despite closure of draining external orifices after infliximab therapy, fistula tracks persist with varying degrees of residual inflammation, which may cause recurrent fistulas and pelvic abscesses. Whether complete fistula fibrosis occurs over time with repeated infliximab infusions needs further study.

Adult↗

PubMed2002

Dry preparation for virtual CT colonography with fecal tagging using water-soluble contrast medium: initial results.

The purpose of this study was to evaluate the feasibility of a dry bowel preparation, i.e. without laxative fluids, for virtual CT colonography (VCTC), and its impact on patient acceptance compared with conventional colonoscopy (CC). A randomly chosen patient population scheduled for CC ( n=11) was first submitted to VCTC after a dry preparation, consisting of low-residue meals combined with a small amount of a iodinated water-soluble contrast medium during each meal 3 days before VCTC. In different colon segments and between different persons, the degree of tagging in VCTC was evaluated and graded. Patient acceptance and future preference were assessed for both preparations as well as for both investigations. The mixing of the contrast with the intestinal content results in contrast impregnated stool, the tagged feces. The degree of fecal tagging was good in the majority of the patients and the colonic segments, especially in the descending colon and sigmoid. Furthermore, patient acceptance and preference were clearly in favour of VCTC compared with CC merely because of the non-invasiveness of the dry preparation. Dry bowel preparation and VCTC is a promising approach towards a patient-friendly colon cancer-screening setup.

Adult↗

PubMed2002

Focal lesions in cirrhotic explant livers: pathological evaluation and accuracy of pretransplantation imaging examinations.

Imaging detection and diagnosis of hepatocellular carcinomas (HCCs) and dysplastic nodules (DNs) in cirrhotic patients is important because the number, size, and type of focal lesions strongly influence patient management. Focal lesions detected by imaging examinations during pretransplantation evaluation were correlated with focal lesions detected during detailed pathological examination of 49 cirrhotic explant livers. Within 6 months before transplantation, color Doppler ultrasonography (US), contrast-enhanced computed tomography (CT), and magnetic resonance (MR) imaging were performed in 94%, 33%, and 55% of patients, respectively. In 2% to 8% of patients, different types of benign focal lesions were present, and a considerable proportion was interpreted as (pre)malignant on imaging examination. US detected only the largest HCCs (patient sensitivity, 40%; specificity, 100%) and no DNs. On a per-patient basis, contrast-enhanced CT and MR imaging had poor sensitivity (20% and 27%, respectively) and good specificity (100% and 94%, respectively) for DNs. Patient sensitivity and specificity of both techniques for HCC were reasonable (50% for CT, 70% for MR imaging) and good (79% for CT, 82% for MR imaging), respectively. Neither technique was able to detect smaller (pre)malignant lesions. As a consequence, 10% of patients underwent transplantation, although they exceeded the tumor number limit. Currently used imaging techniques cannot correctly determine the exact tumor burden in some cirrhotic patients. Regular contrast-enhanced MR examination of cirrhotic patients waiting for liver transplantation is the best tool for the early detection of (pre)malignant lesions.

Adult↗

PubMedDate not supplied

Stool tagging applied in thin-slice multidetector computed tomography colonography.

OBJECTIVE: To compare thin-slice multidetector computed tomography colonography (CTC) that uses stool tagging with colonoscopy. METHOD: One hundred fifty patients scheduled for colonoscopy underwent high-resolution CTC. An iodinated contrast agent was added to the preparation to tag the residual colonic fluid and stool. The effect of fluid tagging was assessed first. Sensitivity and specificity were calculated for two independent readers. In addition, values were recalculated separately for the first and last 75 patients. RESULTS: Tagging was optimal in 95.3% of the cases, and reader confidence was high. Sensitivities were 64.1%-66.7% (for the 2 readers) for 5- to 9-mm polyps and 91.7% for larger polyps. The overall specificity was 94.2% and 95%. Sensitivity improved during the study for both 5- to 9-mm polyps (from 54.2%-58.3% to 80%) and polyps larger than 9 mm (from 50% to 100%). Specificity changed nonuniformly. CONCLUSION: The combination of fluid tagging and high-resolution scanning in CTC showed high sensitivity and specificity, especially concerning sensitivity for polyps of 10 mm and larger.

Colon↗