Biomedical subjects

T Metens

Publications and source records attributed to T Metens.

At least 19 recordsLinked to original sources

PubMed2006

Fat attenuation using a dual steady-state balanced-SSFP sequence with periodically variable flip angles.

A refocused-SSFP sequence based on balanced-FFE (TrueFisp, Fiesta) that attenuates fat signal is presented. The sequence uses periodically variable flip angles and produces a dual steady state of the signal, which is obtained after a dual transient phase if an appropriate preparation is used. The off-resonance profile of the steady-state signal exhibits large stopbands that can be employed for fat suppression. Numerical simulations were performed to investigate the signal behavior and the off-resonance properties of the sequence. Experimental results obtained with a Philips Gyroscan Intera 1.5T MR scanner demonstrated fat attenuation in phantoms and abdominal images in volunteers.

Abdominal Fat↗

PubMed2005

Quantification of pancreatic exocrine function with secretin-enhanced magnetic resonance cholangiopancreatography: normal values and short-term effects of pancreatic duct drainage procedures in chronic pancreatitis. Initial results.

The aim of this study was to quantify pancreatic exocrine function in normal subjects and in patients with chronic pancreatitis (CP) before and after pancreatic duct drainage procedures (PDDP) with dynamic secretin-enhanced magnetic resonance (MR) cholangiopancreatography (S-MRCP). Pancreatic exocrine secretions [quantified by pancreatic flow output (PFO) and total excreted volume (TEV)] were quantified twice in ten healthy volunteers and before and after treatment in 20 CP patients (18 classified as severe, one as moderate, and one as mild according to the Cambridge classification). PFO and TEV were derived from a linear regression between MR-calculated volumes and time. In all subjects, pancreatic exocrine fluid volume initially increased linearly with time during secretin stimulation. In controls, the mean PFO and TEV were 6.8 ml/min and 97 ml; intra-individual deviations were 0.8 ml/min and 16 ml. In 10/20 patients with impaired exocrine secretions before treatment, a significant increase of PFO and TEV was observed after treatment (P<0.05); 3/20 patients presented post-procedural acute pancreatitis and a reduced PFO. The S-MRCP quantification method used in the present study is reproducible and provides normal values for PFO and TEV in the range of those obtained from previous published intubation studies. The initial results in CP patients have demonstrated non-invasively a significant short-term improvement of PFO and TEV after PDDP.

Adult↗

PubMed2005

Functional MRI activation of somatosensory and motor cortices in a hand-grafted patient with early clinical sensorimotor recovery.

The aim of this study was to investigate somatosensory and motor cortical activity with functional MRI (fMRI) in a hand-grafted patient with early clinical recovery. The patient had motor fMRI examinations before transplantation, and motor and passive tactile stimulations after surgery. His normal hand and a normal group were studied for comparison. A patient with complete brachial plexus palsy was studied to assess the lack of a fMRI signal in somatosensory areas in the case of total axonal disconnection. Stimulating the grafted hand revealed significant activation in the contralateral somatosensory cortical areas in all fMRI examinations. The activation was seen as early as 10 days after surgery; this effect cannot be explained by the known physiological mechanisms of nerve regeneration. Although an imagination effect cannot be excluded, the objective clinical recovery of sensory function led us to formulate the hypothesis that a connection to the somatosensory cortex was rapidly established. Additional cases and fundamental studies are needed to assess this hypothesis, but several observations were compatible with this explanation. Before surgery, imaginary motion of the amputated hand produced less intense responses than executed movements of the intact hand, whereas the normal activation pattern for right-handed subjects was found after surgery, in agreement with the good clinical motor recovery.

Adult↗

PubMed2005

Apparent diffusion coefficient (ADC) and magnetization transfer ratio (MTR) in pediatric hypoxic-ischemic brain injury.

BACKGROUND AND PURPOSE: a review of the literature reveals the increasing interest in using Diffusion magnetic resonance imaging, with diffusion weighted images (DWI) and ADC (Apparent Diffusion Coefficient) quantitation, in pediatric hypoxic-ischemic brain injury. However, ADC and MTR (Magnetization Transfer Ratio) as quantitative tools have not been investigated together in these pathological conditions in young pediatric patients. The aim of this study was to apply a quantitative method by using ADC and MTR calculation in order to propose a reproducible quantitation of brain parenchymal lesions. METHODS: we conducted a prospective study including all children presenting with suspected cerebral hypoxic-ischemic injury. 15 children were included, among them 10 males and 5 females aged from 36 weeks of gestation to 17 months with a median age of 10,5 months. All MR examinations were performed at 1.5 Tesla unit including conventional MR (T1, T2 and Inversion-recovery sequences) and DWI with ADC map. ADC and MTR ROI (region of interest) measurements were made, in the frontal subcortical and periventricular white matter (WM) as well as in the gray matter (GM=basal ganglia), and in focal lesions. RESULTS: ADC and MTR values were abnormal in focal lesions and in diffuse injury with no evidence of lesion on conventional MRI and DWI. We observed a strong inverse correlation between these ADC and MTR (R=0,66 in WM; R=0,61 in GM). CONCLUSION: ADC and MTR calculation may be helpful as a reproductive method to quantify the lesions and detect diffuse lesions in hypoxic-ischemic pediatric brain injury.

Diffusion Magnetic Resonance Imaging↗

PubMed2004

[Imaging for stereotaxic treatment of vestibular schwannomas. Error factors and corrections].

BACKGROUND AND PURPOSE: Gamma Knife radiosurgery treatment of vestibular schwannomas requires high accuracy for the prescribed dose definition and delivery. The main factors contributing to the error are the anatomical distortions of imaging modalities used for treatment planning. Imaging limitations and error factors are reviewed and detailed. Multimodality rationale for the delineation of vestibular schwannomas and surrounding structures are assessed. Quality control strategies are discussed and a distortion correction technique using a radiological phantom is presented. METHODS: Computed tomography is considered as the reference for spatial accuracy after appropriate scanner quality control using the stereotaxic fiducials system. Magnetic resonance imaging pulse sequence distortions are measured with a phantom designed for 3D non-linear local distortion evidence. A distortion correction transformation is computed from the phantom images and applied to the patient images. Results are verified using the stereotaxic fiducials system. RESULTS: Fiducials registration errors show spatial accuracy improvement, approaching computed tomography quality, after distortion correction of magnetic resonance images. CONCLUSIONS: The multimodal imaging approach for the dose planning of vestibular schwannomas radiosurgery treatment is relevant. Quality control of spatial accuracy for imaging modalities is mandatory and realistic in clinical routine.

Ear Neoplasms↗

PubMed2003

[Role of new MRI techniques in neuroradiologic practice].

Magnetic Resonance Imaging (MRI) has been introduced in clinical practice in the mid-eighties. However, MRI is an ever evolving imaging technique with constant new developments allowing broadening of clinical applications. In particular, angio-MRI involves many different acquisition techniques that will guide their clinical use. On the other hand, clinical applications of the following techniques are briefly discussed: diffusion, perfusion, tractography and diffusion tensor imaging, spectroscopy and functional imaging.

Brain Diseases↗

PubMed2002

[The medical imaging and radiology department].

Technological developments arising from research have affected the whole wide spectrum of medical endeavor and have made a very significant impact on clinical practice and especially on imaging sciences. Ultrasonography brought spectacular advances, but CT and MRI became important landmark techniques. A further important development, which greatly increased the involvement of radiologists in direct patient management, was the growth of interventional and therapeutic techniques, called interventional radiology. Some statistics: approximately 155,000 patients per year including 19,000 CT Scans, 10,000 MRI exams, 21,000 ultrasound examinations and 1,000 therapeutic procedures. Some research activities: CT quantification of pulmonary emphysema, respiratory mechanics, MR and CT angiography, antenatal diagnosis of congenital and genetic diseases of the fetus, quantification of portal haemodynamics, MR imaging of bile and pancreatic ducts, morphologic and functional imaging of the brain, radiology of bone trauma, MR characterization in hepatic lesions.

Belgium↗

PubMed2001

The role of MR imaging for the assessment of complicated duplex kidneys in children: preliminary report.

OBJECTIVE: To determine whether MR imaging, including MR urography, is able to assess complicated duplex kidneys and to determine the possible role of MRI compared to other imaging techniques in such uropathies. MATERIAL AND METHODS: Twenty consecutive patients (age 1 month-11 years) presenting with a suspicion of a complicated duplex kidney were prospectively studied with MRI and MR urography. The examinations were performed on a 0.5-T machine using routinely available sequences that were optimised to the patient's age and size. MR images were reviewed separately by two observers blinded to the patient history. They were asked to assess the presence of a duplex kidney, the presence of an abnormality that may require surgery and to indicate the type of the inferior ureteric insertion. A qualitative gradation of these results was performed on the basis of the final diagnosis provided at endoscopy (n = 6) or surgery (n = 14). MR results were compared to those provided by US examinations and excretory urography, when available, and a non-parametric statistical analysis was performed. RESULTS: MRI differentiated well between the upper and the lower poles of the kidneys and correctly answered the three questions in all 20 patients. The two observers agreed completely in all the 20 patients. MR was statistically superior to both US and excretory urography in the evaluation of the distal ureter (P < 0.05). CONCLUSIONS: MRI provides a precise assessment of the complications associated with duplex kidneys. Its optimal role seems to be the assessment of ectopic extra-vesical ureteric insertions and whenever an occult upper pole is suspected.

Child↗

PubMed2001

Radiographic diagnosis of rotator cuff tear based on the supraspinatus muscle radiodensity.

OBJECTIVE: To evaluate the supraspinatus muscle radiodensity on the outlet view as an indication of a tendon tear. DESIGN AND PATIENTS: Plain radiographs and magnetic resonance imaging (MRI) examinations were obtained on both shoulders of 40 subjects aged 23-70 years, including 13 asymptomatic volunteers and 27 patients. Two readers analyzed the superior contour and the heterogeneity of the supraspinatus muscle radiodensity and compared them with the MRI findings. RESULTS AND CONCLUSION: Significant concordances (P < 0.001) were found between the assessments of the superior contour and the heterogeneity of the muscle radiodensity, respectively, on plain radiographs and MR images. For the diagnosis of a full-thickness tear, the analysis of the superior contour and the heterogeneity of the muscle radiodensity reached an accuracy of 85% and 80% respectively. Stepwise discriminant analyses showed low to moderate benefit of considering the contour and the heterogeneity simultaneously. The inter- and intraobserver agreement ranged from moderate to good. We conclude that on the outlet view, modifications in the superior contour and heterogeneity of the supraspinatus muscle radiodensity suggest a full-thickness tear.

Adult↗

PubMed2001

Pancreas divisum: evaluation with secretin-enhanced magnetic resonance cholangiopancreatography.

BACKGROUND: The clinical significance of pancreas divisum (PD) remains controversial. Secretin-enhanced magnetic resonance cholangiopancreatography (S-MRCP) is a noninvasive diagnostic procedure that relies on the dynamic response of the main pancreatic duct (MPD) to secretin stimulation. The aim of this study was to determine the frequency of PD and to analyze the dynamic changes of the MPD by using S-MRCP in patients referred for suspected pancreatic diseases before ERCP. METHODS: MRCP was obtained before and at 30-second intervals over 10 minutes after secretin stimulation in consecutive patients with idiopathic acute pancreatitis (n = 67), persistent hydrolasemia (n = 42), recurrent abdominal pain thought to be of pancreatic origin (n = 48), severe chronic pancreatitis (n = 68), and in a control group (n = 54). RESULTS: Thirty patients (10.8%) had a PD at S-MRCP. Secretin stimulation improved the detection of PD in 23% (7/30). The frequency of PD was not significantly different (p > 0.2) between these groups. The occurrence of an abnormal response at S-MRCP (persistent dilatation of the MPD) did not significantly differ in patients with or without PD (p > 0.4). CONCLUSION: The frequency of PD did not differ between groups, and the dynamic changes of the MPD during S-MRCP were similar in patients with and without PD.

Adolescent↗

PubMed2001

Fetal lung volume: estimation at MR imaging-initial results.

PURPOSE: To plot normal fetal lung volume (FLV) obtained with fast spin-echo magnetic resonance (MR) images against gestational age; to investigate the correlation between lung growth and fetal presentation, sex, and ultrasonographic (US) biometric measurements; and to investigate its potential application in fetuses with thoracoabdominal malformations. MATERIALS AND METHODS: In a prospective multicenter study, 336 fetuses suspected of having central nervous system disorders underwent fast spin-echo T2-weighted lung MR imaging. Data obtained at 21-38 weeks gestation in 215 fetuses without thoracoabdominal malformations and with normal US biometric findings were selected for an FLV normative curve. FLV measurements obtained at pathologic examination with an immersion method were compared with MR FLV measurements in 11 fetuses. MR FLV values in 16 fetuses with thoracoabdominal malformations were compared with the normative curve. RESULTS: Normal FLV increased with gestational age as a power curve; the spread of values increased with age. Interobserver correlation was excellent (R(2) = 0.96). FLV measurements at MR imaging were 0.90 times those at pathologic examination. A constant ratio (0.78) between FLV on the left and right sides was observed. No significant difference in FLV was observed between fetal presentations. Normal FLV was observed in all fetuses with cystic adenomatoid malformations and in four of six with oligohydramnios. Lowest FLV values were observed in fetuses with diaphragmatic hernia. CONCLUSION: In fetuses with normal lungs, FLV distribution against gestational age is easily assessed in utero with fast spin-echo T2-weighted MR imaging. These preliminary findings illustrate the potential for comparing FLV measurements in fetuses at risk of lung hypoplasia with normative values.

Abnormalities, Multiple↗

PubMed2000

Chronic pancreatitis: evaluation of pancreatic exocrine function with MR pancreatography after secretin stimulation.

PURPOSE: To compare duodenal filling seen at magnetic resonance (MR) pancreatography after secretin stimulation and biochemical parameters determined with the intraductal secretin test (IDST) for evaluation of pancreatic exocrine function. MATERIALS AND METHODS: MR pancreatography after secretin stimulation and IDST were performed in 41 patients with chronic pancreatitis (group 1) and eight patients with other pancreatic disease (group 2). A control group (group 3, n = 28) underwent MR pancreatography after secretin stimulation only. MR pancreatograms were acquired before and every 30 seconds for 10 minutes after secretin injection. Duodenal filling was graded from least amount of filling (grade 1) to normal filling (grade 3) on the last MR pancreatogram. Pancreatic exocrine function was determined at IDST. Main pancreatic ductal diameter was compared between groups 1 and 3. RESULTS: All ductal diameters were significantly larger in group 1 (P <.001). The maximal diameter variation after secretin stimulation was significantly higher in the control group (P =.001). Pancreatic exocrine function parameters determined at IDST were significantly lower in patients with grade 1 duodenal filling than in those with grade 2 or 3 (P <.05). Maximal bicarbonate concentration alone was independently associated with all grades of duodenal filling (P =.007). The sensitivity and specificity of reduced duodenal filling for assessment of reduced pancreatic exocrine function were 72% and 87%, respectively. CONCLUSION: Duodenal filling grade determined at MR pancreatography after secretin stimulation allows specific estimation of pancreatic exocrine function.

Adolescent↗

PubMed2000

Intracranial aneurysms: detection with gadolinium-enhanced dynamic three-dimensional MR angiography-initial results.

PURPOSE: To assess the clinical utility and accuracy of contrast material-enhanced dynamic three-dimensional (3D) T1-weighted magnetic resonance (MR) angiography in the detection of unruptured intracranial aneurysms. MATERIALS AND METHODS: A prospective blinded comparison of 3D contrast-enhanced T1-weighted MR angiography with 3D inflow magnetization transfer and tilted optimized nonsaturating excitation (MT TONE) imaging, phase-contrast MR angiography, and conventional digital subtraction angiography (DSA) was performed in 32 consecutive patients. The first dynamic 3D contrast-enhanced T1-weighted acquisition was individually timed after injection of a bolus of gadolinium-based contrast agent to obtain an arterial phase image followed by two sequential venous phase images (three 18-second acquisitions). Two readers independently interpreted and graded the MR images for diagnostic confidence and depiction of aneurysms and subsequently compared them with DSA images. RESULTS: Three-dimensional contrast-enhanced T1-weighted MR angiograms depicted all 23 aneurysms detected in 17 patients at DSA (mean size, 6 mm; range, 2-21 mm) with one false-positive result by one reader (sensitivity, 100%; specificity, 94%). MT TONE and phase-contrast images failed to depict one and seven aneurysms, respectively (MT TONE sensitivity of 96% and specificity of 100%, phase-contrast sensitivity of 70% and specificity of 100%). Aneurysm depiction at 3D contrast-enhanced T1-weighted MR angiography was significantly better than that at MT TONE imaging (P <.012), and that with both was significantly superior to that of phase-contrast imaging (P <. 001). Differences in diagnostic confidence in the presence of an aneurysm were not significant between 3D contrast-enhanced T1-weighted and MT TONE imaging (P =.076). CONCLUSION: Dynamic 3D contrast-enhanced T1-weighted MR angiography is a fast, efficient, and minimally invasive imaging method with which to diagnose intracranial aneurysms.

Adult↗

PubMed2000

Gamma knife radiosurgery as a primary treatment for prolactinomas.

OBJECT: The purpose of this study was to estimate the efficacy of gamma knife radiosurgery (GKS) in controlling tumor growth and endocrinopathy associated with prolactinomas. METHODS: Between 1993 and 1997, 164 of 469 patients with pituitary adenomas treated by GKS harbored prolactinomas. The dose to the tumor margin ranged from 9 to 35 Gy (mean 31.2 Gy), and the visual pathways were exposed to a dose of less than 10 Gy. The mean tumor diameter was 13.4 mm. The mean follow-up time for 128 cases was 33.2 months (range 6-72 months). Tumor control was observed in all but two patients who underwent surgery 18 and 36 months, respectively, after GKS. Clinical cure was achieved in 67 cases. Clinical improvement was noted with a decrease in the hyperprolactinemia after GKS. Nonetheless, in 31 (29%) of 108 patients who were followed for more than 2 years no improvement in serum prolactin levels was demonstrated, although this could be normalized by bromocriptine administration after treatment. Nine infertile women became pregnant 2 to 13 months after GKS and all gave birth to normal children. There was no visual deterioration related to GKS. Five women experienced premature menopause. In these patients there was subtotal disappearance of the tumor and an empty sella developed. CONCLUSIONS: Gamma knife radiosurgery as a primary treatment for prolactinomas can be safe and effective both for controlling tumor growth and for normalization of prolactin hypersecretion. A higher margin dose (> or = 30 Gy) seemed to be associated with a better clinical outcome. Gamma knife radiosurgery may make prolactinomas more sensitive to the bromocriptine.

Humans↗

PubMed1999

Secretin-enhanced MR pancreatography.

MR cholangiopancreatography has now emerged as a noninvasive diagnostic technique that can replace diagnostic endoscopic retrograde cholangiopancreatography in many instances. Recent technical issues include the use of fast single-shot T2-weighted single-slice projections in combination with a negative oral contrast agent and secretin stimulation for assessment of pancreatic flow dynamics and duodenal filling. Potential clinical applications include the evaluation of patients with recurrent pancreatitis and inconclusive CT examination as well as the evaluation of chronic pancreatitis complications whenever endoscopic treatment is suggested. In combination with cross-sectional MR sequences, secretin-enhanced MR pancreatography offers the possibility of a comprehensive examination of the pancreas that provides parenchymal, ductal, and functional information within a single diagnostic modality.

Humans↗

PubMed1999

[Magnetic resonance angiography of the renal arteries].

Initially, the clinical use of magnetic resonance angiography (MRA) in the abdomen has been restricted because of motion and flow related artifacts. The advent of high performance gradient systems made possible the development of 3D gadolinium-enhanced MRA techniques and expanded the clinical applications of MRA into the abdominal area, particularly for the investigation of renal arteries. This technique is safe, because the administered contrast agent (gadolinium) is free of clinically detectable nephrotoxicity and has a low incidence of allergic reactions. Moreover, contrast MRA also eliminates the risks of ionizing radiation which allows repeating the examination without the accumulation of radiation exposure. The main disadvantages of the technique are its low availability and the fact that the use of contrast agents for this procedure is still not reimbursed by the social security. Many studies demonstrated that contrast MRA allows for the reliable assessment of renal artery morphology and pathologic states. Furthermore, within a single MR examination a comprehensive approach including renal artery morphology, hemodynamic significance of any stenosis and kidney perfusion is available. In this paper, we provide a review of the literature concerning the clinical performance of contrast MRA for the renal arteries and suggest its rationale for the investigation of patients suspected of renovascular disease in our specific environment.

Artifacts↗

PubMed1998

Magnetic resonance cholangiopancreatography: interest of IV secretin administration in the evaluation of pancreatic ducts.

The aim of this study was to investigate whether IV secretin administration is useful to enhance the delineation of the main pancreatic duct (MPD) and its side branches, and if it provides additional information concerning signal voids and strictures. Twenty-seven patients referred for abdominal pain or laboratory abnormalities (group 1, n = 13) or for the follow-up of chronic pancreatitis (CP; group 2, n = 14) were studied. Magnetic resonance cholangiopancreatography was acquired at 1.5 T before and after IV secretin by a coronal 3D TSE T2-weighted sequence with maximum intensity projection postprocessing. In group 1 secretin provided a better visualization of MPD in 9 patients. In a patient with pancreas divisum, it allowed suggestion of stenosis of the accessory papilla, confirmed at endoscopic retrograde cholangiopancreatography (ERCP). In group 2 secretin provided a better visualization of MPD only in the 3 patients with mild disease. A mild dilation upstream a stricture occurred in 2 cases and a marked dilation appeared upstream a wallstent which was non-patent at ERCP. Few changes were noticed concerning side branches. These preliminary results indicate that in patients without CP, secretin improves MPD delineation avoiding invasive diagnostic ERCP. In patients with mild CP secretin does not improve the characterization of signal voids, but it may be useful to appreciate their significance and to follow-up stenosis.

Adult↗

PubMed1998

Perisylvian dysgenesis. Clinical, EEG, MRI and glucose metabolism features in 10 patients.

We studied 10 patients who had neurological disorders with a MRI-based diagnosis of perisylvian dysgenesis based on the fact that the parasagittal and centrifugal extremity of the sylvian fissure was abnormally mesial. This abnormality was bilateral in seven cases; in the other three patients, the contralateral sylvian fissure appeared either normal (two cases) or enlarged (open operculum). The perisylvian cortex had a polymicrogyric appearance in most patients. Potential aetiopathogenic factors were determined in four patients. In two of them, ischaemia at mid-gestation was ascribed to death of a co-twin in a context of monozygotic twinning. In the other two patients, who were siblings, genetic factors were suspected. Pseudobulbar palsy was found in eight patients and epilepsy in five patients. We used PET with [18F]fluorodeoxyglucose to test the hypothesis that, despite this clinical and MRI heterogeneity, regional cerebral glucose distribution could have common features in these patients. The analysis of PET data was performed by visual inspection in two cases and by using statistical parametric mapping (SPM) in eight patients compared with a control group. Segmented grey matter MRIs of seven out these patients were also analysed using SPM. We found that the abnormal perisylvian cortex had normal grey matter activity in eight patients and in the other two there was a heterogeneous pattern with areas of preserved metabolism and of decreased metabolism. Metabolic changes were also detected outside the polymicrogyric-like cortex; three patients had hypometabolic areas in cortical regions where the MRI appeared normal and had a normal intensity. When polymicrogyria extended into the white matter, this ectopic dysgenetic cortex was associated with a grey matter pattern within the white matter territory, and was detected by SPM as areas of PET hypermetabolism and MRI hyperintensity. In order to detect possible metabolic changes undetected by the individual analyses, the group of patients was compared with the control group. This comparison revealed bilateral hypometabolism in the frontal opercular cortex. We propose that these PET data be considered in light of the presumed cyto-architectonic pattern of perisylvian dysgenesis, i.e. polymicrogyria. In this malformation, two dense cell layers are separated by a necrotic sparse cell layer. We speculate that the amount of synaptic activity preserved in these dense cell layers depends on the importance and timing of the necrotic process; this hypothesis accounts for the large range of metabolic patterns found, from profoundly decreased glucose metabolism to nearly normal activity.

Adolescent↗