Biomedical subjects

Thierry Metens

Publications and source records attributed to Thierry Metens.

At least 19 recordsLinked to original sources

PubMed2006

Quantitative diffusion imaging in breast cancer: a clinical prospective study.

PURPOSE: To study the correlation between apparent diffusion coefficient (ADC) and pathology in patients with undefined breast lesion, to validate how accurately ADC is related to histology, and to define a threshold value of ADC to distinguish malignant from benign lesions. MATERIALS AND METHODS: Seventy-eight patients (110 lesions) were referred for positive or dubious findings. Three-dimensional fast low-angle shot (3D-FLASH) with contrast injection was applied. EPI diffusion-weighted imaging (DWI) with fat saturation was performed, and ROIs were selected on subtraction 3D-FLASH images before and after contrast injection, and copied on an ADC map. Inter- and intraobserver analyses were performed. RESULTS: At pathology 22 lesions were benign, 65 were malignant, and 23 were excluded. The ADCs of malignant and benign lesions were statistically different. In malignant tumors the ADC was (mean +/- SEM) 0.95 +/- 0.027 x 10(-3)mm(2)/second, and in benign tumors it was 1.51 +/- 0.068 x 10(-3)mm(2)/second. According to receiver operating characteristic (ROC) curves, we found a threshold between malignant and benign lesions for highest sensitivity and specificity (both 86%) around 1.13 +/- 0.10 x 10(-3)mm(2)/second. For a threshold of 0.95 +/- 0.10 x 10(-3)mm(2)/second, specificity was 100% but sensitivity was very low. Inter- and intraobserver studies showed good reproducibility. CONCLUSION: The ADC may help to differentiate benign and malignant lesions with good specificity, and may increase the overall specificity of breast MRI.

Adult↗

PubMed2006

Correlation between dynamic susceptibility contrast perfusion MRI and methionine metabolism in brain gliomas: preliminary results.

PURPOSE: To evaluate in brain gliomas the relationship between tumor vascularity measured by MR-based maximum regional cerebral blood volume (rCBV) and tumor amino-acid metabolism based on maximum carbon-11 methionine (MET) uptake on positron emission tomography (PET). MATERIALS AND METHODS: Eighteen patients with histologically proven primary brain gliomas were included in the study. In addition to conventional MR sequences, dynamic MR images, including a first-pass gadopentetate dimeglumine T2*-weighted echo-planar perfusion sequence and a PET study using MET, were acquired. Eleven patients had low-grade gliomas, and seven had high-grade gliomas. rCBV ratios and MET uptake ratios normalized to the contralateral white matter (WM) corresponding values were measured in each tumor. Both maximum rCBV ratios and maximum MET uptake ratios were correlated to histopathology. The maximum rCBV ratios were correlated to the maximum MET uptake ratios. RESULTS: Both the maximum rCBV ratios and maximum MET uptake ratios of high-grade gliomas were significantly higher than those of low-grade gliomas (P<0.05). There was a significant positive correlation between maximum rCBV ratios and maximum MET uptake ratios (Spearman: r=0.89, P<0.00001). CONCLUSION: The maximum rCBV ratio and maximum MET uptake ratio are significantly correlated in gliomas, reflecting a close link between amino acid uptake and vascularity in these tumors.

Adult↗

PubMed2006

Present and potential future issues in glioblastoma treatment.

The treatment of glioblastomas requires a multidisciplinary approach that takes the presently incurable nature of the disease into consideration. Treatments are multimodal and include surgery, radiotherapy and chemotherapy. Current recommendations are that patients with glioblastomas should undergo maximum surgical resection, followed by concurrent radiation and chemotherapy with the novel alkylating drug temozolomide. This is then to be followed by additional adjuvant temozolomide for a period of up to 6 months. Major advances in surgical and imaging technologies used to treat glioblastoma patients are described. These technologies include magnetic resonance imaging and metabolic data that are helpful in the diagnosis and guiding of surgical resection. However, glioblastomas almost invariably recur near their initial sites. Disease progression usually occurs within 6 months and leads rapidly to death. A number of signaling pathways can be activated constitutively in migrating glioma cells, thus rendering these cells resistant to proapoptotic insults, such as conventional chemotherapies. Therefore, the molecular and cellular therapies and local drug delivery that could be used to complement conventional treatments are described, and some of the currently ongoing clinical trials are reviewed, with respect to these new approaches.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed2005

Pineapple juice labeled with gadolinium: a convenient oral contrast for magnetic resonance cholangiopancreatography.

The aim of our study was to prepare in vitro a pineapple juice (PJ) solution labeled with a minimal gadolinium concentration working as a negative contrast agent in heavily T2-weighted imaging and to assess that solution in vivo as a negative oral contrast agent for magnetic resonance cholangiopancreatography (MRCP). Three PJs were compared in vitro according to their T2. Increasing concentrations of gadolinium (Gd)-DOTA in PJ were assessed in vitro for T2 reduction. Single-shot turbo spin echo T2-weighted MR cholangiopancreatograms were obtained for 35 patients with suspected biliopancreatic duct disease, before and after ingestion of the PJ/Gd-DOTA solution. Signal intensity (SI) measurements of gastroduodenal lumens, pancreatobiliary ducts, and image quality scores were obtained systematically before and after contrast ingestion. The in vitro selected Gd-DOTA concentration in the PJ was 2.76 mmol/l. Ingestion of 180 ml of PJ labeled with 1 ml of Gd-DOTA eliminated efficiently the gastroduodenal SI in MRCP, improving significantly the rates of complete visualization of the pancreatobiliary ducts (P<0.01) and the MRCP image quality scores (P<0.05). All patients easily ingested the contrast solution and found the solution palatable. PJ labeled with gadolinium constituted an efficient and convenient negative oral contrast agent for MRCP.

Administration, Oral↗

PubMed2005

New insights into the mechanisms of signal formation in RF-spoiled gradient echo sequences.

RF spoiling is a well established method to produce T(1)-weighted images with short repetition-time gradient-echo sequences, by eliminating coherent transverse magnetization with appropriate RF phase modulation. This paper presents 2 novel approaches to describe signal formation in such sequences. Both methods rely on the formulation of RF spoiling as a linear increase of the precession angle between RF pulses, which is an alternative to the commonly used quadratic pulse phase scheme. The first technique demonstrates that a steady state signal can be obtained by integrating over all precession angles within the voxel, in spite of the lack of a genuine steady-state for separate isochromats. This clear mathematical framework allows a straightforward incorporation of off-resonance effects and detector phase settings. Moreover, it naturally introduces the need for a large net gradient area per repetition interval. In the second step, a modified partition method including RF spoiling is developed to obtain explicit expressions for all signal components. This provides a physical interpretation of the deviations from ideal spoiling behavior in FLASH and echo-shifted sequences. The results of the partition method in the small flip angle regime are compared with numerical simulations based on a Fourier decomposition of magnetization states. Measurements performed with in vitro solutions were in good agreement with numerical simulations at short relaxation times (T(1)/TR = 32 and T(2)/TR = 4); larger deviations occurred at long relaxation times (T(1)/TR = 114 and T(2)/TR = 82).

Algorithms↗

PubMed2005

Combination of functional magnetic resonance imaging-guided neuronavigation and intraoperative cortical brain mapping improves targeting of motor cortex stimulation in neuropathic pain.

OBJECTIVE: To evaluate, regardless of the clinical results, the contribution of combining functional magnetic resonance imaging (fMRI) with intraoperative cortical brain mapping (iCM) as functional targeting methods for epidural chronic motor cortex stimulation (MCS) in refractory neuropathic pain. METHODS: Eighteen neuropathic pain patients (central stroke in six; trigeminal neuropathy in six; syrinx or amputation in six) who underwent operations for epidural MCS were studied with preoperative fMRI and iCM. fMRI investigated motor tasks of hands (as well as foot and tongue, when painful). fMRI data were analyzed with Statistical Parametric Mapping99 software (University College London, London, England; initial analysis threshold corresponding to P < 0.001), registered in a neuronavigation system, and correlated during surgery with iCM. The primary aim of this study was to improve the topographical precision of MCS. Matching of fMRI and iCM specifically was examined. RESULTS: Correspondence between the contour of the fMRI activation area and iCM in precentral gyrus (mean distance, 3.8 mm) was found in 17 (94%) of 18 patients. Eleven of them showed correspondence for more restrictive values of the analysis threshold (P < 0.0001); in six patients, the quality of the iCM was reduced by somatosensory wave attenuation and general anesthesia. In this group of six patients, a combination of both techniques was used for the final targeting. Correspondence was not found in one patient as the result of image distortion and residual motion artifact. At follow-up (4-60 mo), MCS induced significant pain relief in a total of 11 patients (61%). CONCLUSION: This study confirms the functional accuracy of fMRI guidance in neuropathic pain and illustrates the usefulness of combining fMRI guidance with iCM to improve the functional targeting in MCS. Because appropriate targeting is crucial to obtaining pain relief, this combination may increase the analgesic efficacy of MCS.

Adult↗

PubMed2005

MR cholangiography with manganese dipyridoxyl diphosphate in the evaluation of biliary-enteric anastomoses: preliminary experience.

OBJECTIVE: The purpose of our study was to assess the usefulness of manganese dipyridoxyl diphosphate (Mn-DPDP)-enhanced T1-weighted MR cholangiography for evaluating patients with biliary-enteric anastomoses. CONCLUSION: Mn-DPDP-enhanced T1-weighted MR cholangiography may provide useful functional information and may aid in the assessment of the patency of biliary-enteric anastomoses.

Adult↗

PubMed2005

Comparison of functional MR imaging guidance to electrical cortical mapping for targeting selective motor cortex areas in neuropathic pain: a study based on intraoperative stereotactic navigation.

PURPOSE: To assess the concordance between data from functional MR imaging (fMRI) guidance and the intraoperative electrical cortical mapping (iCM) in targeting selective motor cortex areas in refractory neuropathic pain. METHODS: Twenty-one patients (11 women and 10 men; mean age, 55.6 years) with refractory central (ischemic, 8 cases) and neuropathic pain (trigeminal neuropathy, 6 cases; syrinx/amputation/plexus trauma, 7 cases) underwent surgery for the implantation of an epidural electrode for chronic motor cortex stimulation (MCS) with general anesthesia and a frameless neuronavigation system used for the image-guided targeting procedure. All patients were studied by preoperative fMRI and epidural iCM with somatosensory evoked potentials and motor cortex stimulodetection. fMRI investigated systematically motor tasks of both hands and that related to the somatic area (foot or tongue) affected by pain. fMRI data were analyzed with the Statistical Parametric Mapping99 software (initial analysis threshold [AT] corresponding to P < .001), registered in the neuronavigation system and correlated intraoperatively with iCM. Matching of fMRI and iCM was specifically examined, focusing the study on hand mapping. RESULTS: Concordance between contours of fMRI activation area and iCM in precentral gyrus (mean distance, 3.8 mm) was found in 20/21 patients (95%). Because precision of iCM was suboptimal in 7 patients, concordance for more restrictive values of the AT (P < .0001) was found in only 13 of these 20 patients. Concordance was not found in one patient, as result of image distortion and residual motion artifact. CONCLUSIONS: In this study, fMRI guidance provides information that matches those of an independent functional method. These data illustrate the functional accuracy of fMRI guidance for the operative targeting of selective motor cortex areas in neuropathic pain.

Adult↗

PubMed2004

On the calculation and interpretation of signal intensity in echo-shifted sequences.

Echo-shifted sequences have been shown to be useful in applications where strong T*2-weighting and short repetition times are wanted, such as BOLD-contrast fMRI, MR thermometry, and perfusion studies. However, a full understanding of signal formation with such methods, which is mandatory to optimize sequence parameters for particular applications, has still not been achieved. Here, two methods are proposed to calculate the steady-state signal intensity in coherent TR-periodic and TR-shifted gradient-echo sequences. The integration method, which consists of averaging the steady-state magnetization over all isochromats in a voxel, is shown to be a particularly efficient way of obtaining the analytical expression of the measurable signal. The partition method, based on a physical decomposition of the steady-state magnetization into a sum of contributions from past excitation pulses, reveals that the net transverse magnetization results from a destructive interference between the wanted component and a series of stimulated echoes. The analysis includes off-resonance effects and is illustrated by phantom measurements. Relationships with previous publications on this subject are discussed.

Echo-Planar Imaging↗

PubMed2004

Complementary role of MRI after sonography in assessing bilateral urinary tract anomalies in the fetus.

OBJECTIVE: The objectives of our study were to evaluate the contribution of adding MRI findings to inconclusive sonographic data when assessing fetal urinary tract anomalies and to determine how this addition may affect the management of pregnancy. SUBJECTS AND METHODS. We prospectively used MRI to study 16 third-trimester fetuses in whom sonography suggested bilateral urinary tract anomalies but failed to provide a definite diagnosis. These anomalies included enlarged hyperechoic kidneys (n = 6), bilateral pelvicaliceal dilatation (n = 6), renal cystic lesions (n = 2), and renal agenesis associated with severe oligohydramnios (n = 2). RESULTS: The addition of MRI to sonography modified the diagnosis in five fetuses. In a fetus with suspected bilateral ureteropelvic obstruction, the diagnosis of bilateral ureterohydronephrosis associated with reflux or ureterovesical junction obstruction was made. In a fetus with an enlarged bladder at 32 weeks' gestational age, a possible diagnosis of megacystic microcolon was excluded on the basis of the normal appearance of the colon. In two fetuses with enlarged hyperechoic kidneys, MRI showed localized medullary hyperintense lesions suggesting autosomal recessive polycystic kidney disease in one fetus and medullary cystic dysplasia in another fetus with Jeune's syndrome. In a patient with suspected unilateral renal agenesis, MRI showed bilateral agenesis. In four fetuses, the addition of MRI to sonography led to a diagnosis that modified the decision to continue or terminate the pregnancy. CONCLUSION: MRI can accurately show many urinary tract anomalies in third-trimester fetuses. It may be a useful complementary tool in the assessment of bilateral urinary tract anomalies of fetuses, particularly in cases with inconclusive sonographic findings.

Adult↗

PubMed2003

The iliac angle: a sonographic marker of trisomy 21 during the midtrimester: dependency of fetal lying?

The aim of this study was to evaluate the efficiency of the fetal iliac wing angle measurements in the detection of trisomy 21 during the second trimester and the impact of the fetal position on this measurement. During a 43-month period, the iliac wing angle was prospectively measured in 695 fetuses at genetic ultrasonography performed before amniocentesis. The iliac wing angle measurements were performed in a true axial section of the fetal pelvis and the relative position of the fetal spine was recorded (decubitus, lateral). Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and likelihood ratio (LR) were computed for multiple cutoff angles. The prevalence of trisomy 21 was 1.4%; 447 fetuses were in lateral position, 240 fetuses were in decubitus position, including, respectively, 2 and 8 fetuses with trisomy 21 (8 fetuses with other chromosomal anomalies were excluded). In euploid fetuses, the mean iliac wing angle was 83.7 degrees in decubitus and 68.7 degrees in lateral position; in fetuses with trisomy 21 the respective mean angles were 104.9 degrees and 102.5 degrees. A receiver operating characteristics (ROC) curve provided an absolute cutoff angle of 90 degrees, predicting trisomy 21 with a sensitivity of 100%, a specificity of 72.4%, an NPV of 100%, a PPV value of 11.1%, and an LR of 3.6. The measurement of iliac wing angles in an axial section of the fetal pelvis is dependent on spine orientation and provides an efficient cutoff angle for the exclusion of trisomy 21 in patients at risk.

Adolescent↗

PubMed2003

Three-dimensional BOLD fMRI with spin-echo characteristics using T2 magnetization preparation and echo-planar readouts.

A new approach to mixed T(2)- and T(2) (*)-weighted BOLD fMRI is presented, which combines T(2) magnetization preparation (T2prep) with a series of EPI readouts. This technique allows full 3D, time-efficient imaging to be performed with low RF power deposition. Steady-state calculations are performed in order to study signal formation in 3D T2prep-EPI sequences. Results obtained under the hypothesis of ideal spoiling are compared to full Bloch equation solutions. The theoretical findings are validated by means of in vitro and in vivo signal measurements. Several variants of the 3D T2prep-EPI approach are shown to be usable for visual cortex fMRI and compared to conventional 3D coherent gradient-echo EPI. The relative sensitivity of these sequences is shown to be predictable by means of a simple DeltaT(2)/DeltaT(2) (*) model.

Brain↗

PubMed2003

Determination of velum opening for French nasal vowels by magnetic resonance imaging.

MRI techniques have been used to describe velum opening of French vowels. Data based on 18 joined axial slices of 4 mm thickness were recorded with four subjects. Differences in velum opening are calculated from areas measured in the tract between the lowered velum and the back pharynx wall. Results show that for all subjects, the back vowel [symbol: see text] has the smallest opening, while some variations are observed for the other vowels.

Female↗

PubMed2003

Characterization of gastrin-induced cytostatic effect on cell proliferation in experimental malignant gliomas.

OBJECTIVE: Growth patterns of astrocytic tumors can be modulated in vitro by gastrin. In this study, the influence of gastrin on the in vitro cell cycle kinetics and the in vivo growth features of three experimental malignant gliomas was investigated. METHODS: Gastrin-induced influence on overall growth was assayed in vitro by means of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium colorimetric assay for human U373 and rat C6 gliomas and for rat 9L gliosarcoma. Although cell cycle analyses were performed by means of computer-assisted microscope analyses of Feulgen-stained nuclei, the gastrin-induced effects of the levels of expression of cyclins D3 and E, CDK2, CDK4, CDK5, CDK7, p15, p16, E2F1, and E2F2 were assayed by means of quantitative Western blot test. The presence of ribonucleic acids for the CCK(B) and CCK(C) gastrin receptors in the U373, C6, and 9L models was assayed by means of quantitative reverse transcriptase-polymerase chain reaction, and the presence or absence of ribonucleic acids for CCK(A) receptor was checked by means of conventional polymerase chain reaction. The influence of gastrin was also characterized in vivo in terms of the survival periods of conventional rats orthotopically grafted with the C6 and 9L models and nude rats with the U373 model. RESULTS: Gastrin significantly decreased the overall growth rate in the rat C6 and the human U373 high-grade astrocytic tumor models with either CCK(B) or CCK(C) gastrin receptor but not in the 9L rat gliosarcoma, which had no CCK(B) gastrin receptor (but had CCK(A) receptor) and only weak amounts of CCK(C) receptor. This effect seems to occur via a cytostatic effect; that is, an accumulation of tumor astrocytes occurs in the G(1) cell cycle phase. The cytostatic effect could relate to a gastrin-induced decrease in the amounts of the cyclin D3-CDK4 complex in both C6 and U373 glioma cells. In vivo, gastrin significantly increased the survival periods of C6 and U373 glioma-bearing rats, but not of 9L gliosarcoma-bearing rats. CONCLUSION: Gastrin is able to significantly modify the growth levels of a number of experimental gliomas.

Animals↗

PubMed2003

Effect of hydrophilic components of the extracellular matrix on quantifiable diffusion-weighted imaging of human gliomas: preliminary results of correlating apparent diffusion coefficient values and hyaluronan expression level.

OBJECTIVE: The purpose of this study was to evaluate the relationship between apparent diffusion coefficient (ADC) measured by MR imaging and the level of immunohistochemical expression of hyaluronan or hyaluronic acid as one of the main hydrophilic components of the extracellular matrix in brain glial tumors. MATERIALS AND METHODS: Nineteen patients with primary glial brain tumors were included in the study. Mean ADC values were calculated in all tumors and were normalized with the ADC values of the contralateral normal-appearing brain ratios. All tumors underwent surgical resection, and the histologic diagnosis was based on the analysis of the surgical specimen. Mean values of the labeling index of hyaluronan (LI-HA) were calculated to determine quantifiably the histochemical expression of hyaluronan in the tumor. The mean ADC values and the mean ADC ratios (ADC(ratio)) of the tumors were then correlated to the mean values of the LI-HA. RESULTS: The mean ADC (93 x 10(-5) mm(2)/sec) and the mean ADC(ratio) (1.25) of the high-grade glial tumors were significantly lower than the mean ADC (123 x 10(-5) mm/sec) and the mean ADC(ratio) (1.64) of the low-grade glial tumors (p < 0.01). The mean LI-HA (72.8%) was also significantly lower in the high-grade gliomas than the mean LI-HA (93.4%) in the low-grade gliomas (p < 0.001). A positive correlation was found between mean ADC values and the mean LI-HA (tau = 0.35, p < 0.05) and also between the mean ADC(ratio) and the mean LI-HA (tau = 0.33, p < 0.05). CONCLUSION: Hyaluronan as one of the main hydrophilic components of the extracellular matrix in gliomas likely contributes to differences in the ADC values between high- and low-grade glial tumors.

Brain↗

PubMed2002

MR urography in children.

Thanks to the development of rapid sequences with better resolution, applications of uro MR have rapidly increased in children. Difficulties that remain are related to the variable ages of the patients. It is therefore mandatory to standardize as much as possible the techniques that are used in order to obtain reproducible results. In this review, the examination protocols will be explained. In a second part the current applications in children will be illustrated and discussed, especially in comparison with the other imaging techniques.

Child↗

PubMed2002

Real-time MRI and articulatory coordination in speech.

This paper describes the real-time MRI technique and its use for the study of speech production. The two major problems, (i) the simultaneous recording of the MR images and the speech signal and (ii) the synchronisation of the images and of the speech signal, are addressed. Measurement accuracy on real-time images is evaluated by comparison with similar measurements on static MR images.

Computer Systems↗

PubMed2002

The evaluation by magnetic resonance imaging of hepatic periportal fibrosis in infants with neonatal cholestasis: preliminary report.

PURPOSE: The aim of this study was to evaluate the potential role of magnetic resonance (MR) imaging cholangiography for the assessment of periportal fibrosis associated with neonatal cholestasis. METHODS: The authors have compared the findings on MR imaging cholangiography and on pathology in 10 infants evaluated because of neonatal cholestasis. The series included 3 patients with biliary atresia (BA), 3 patients with choledocal cyst, 2 with a neonatal hepatitis, and 2 with an inspissated bile syndrome. MR examinations were performed on a 0.5 Tesla magnet unit using Turbo Field Echo T1 and Turbo spin echo T2 sequences. A periportal hyposignal paralleling the portal vein branches and disappearing after Gadolinium injection was considered consistent with periportal fibrosis. The final type of hepatobiliary anomaly was established based on surgery (n = 6) or on laparoscopic cholangiogram (n = 10). The degree of periportal fibrosis was evaluated on pathology using a grading system from grade 0 (no fibrosis) to 4 (fibrosis with cirrhosis). The relationship between periportal hyposignal and fibrosis was tested using the exact chi2 test. RESULTS: MR imaging assessed correctly and more completely than ultrasound scan the morphology of the biliary tract in all 10 patients. A periportal hyposignal was present in the 3 patients with BA (2 patients displayed a grade 3 and one a grade 4 fibrosis on pathology) and in one with choledocal cyst (grade 3 fibrosis on pathology). No hyposignal was visualized in the 2 other patients with a choledocal cyst (grades 1 and 2), in the 2 patients with neonatal hepatitis (grades 1 and 2), or in the 2 patients with inspissated bile syndrome (both grade 0). A relationship between the hyposignal seen on MR and the degree of fibrosis seen on pathology was confirmed by the exact chi2 test (P =.019). CONCLUSIONS: This preliminary series confirms the potential role of MR imaging for the assessment of the morphology of the abnormal biliary tract and of the degree of periportal fibrosis. The presence of an hyposignal on an echo gradient TFE T1 sequence suggests an advanced fibrosis (grade 3 and higher).

Biliary Atresia↗