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Biomedical subjects

G Marchal

Publications and source records attributed to G Marchal.

At least 163 records · Page 9Linked to original sources
PubMed1996

Supra- and juxtarenal aneurysms of the abdominal aorta: preoperative assessment with thin-section spiral CT.

PURPOSE: To assess the contribution of thin-section spiral computed tomography (CT) to the preoperative radiologic evaluation of juxta- and suprarenal abdominal aortic aneurysms. MATERIALS AND METHODS: Thirty-eight patients (26 men, 12 women; age range, 60-81 years) with infrarenal (n = 23), juxtarenal (n = 8), and suprarenal (n = 7) aneurysms underwent digital subtraction angiography (DSA) and 2-mm-collimation spiral CT. Cine-interactive display of overlapping axial, reformatted, and maximum intensity projection images were used for CT image analysis. CT findings were compared with angiographic and surgical findings. RESULTS: The proximal extent of the juxta- and suprarenal aneurysms (n = 15) could be correctly predicted in 12 cases (80%) with DSA and was exactly determined in 14 (93%) with CT. All renal arteries except three accessory renal arteries were correctly depicted with spiral CT (83 of 86 [96%]). With DSA as the standard of reference, renal artery stenoses of at least 70% were accurately assessed in 95% of cases. CONCLUSION: Thin-section spiral CT can provide additional information in the preoperative diagnosis of juxta- and suprarenal aneurysms.

Aged↗
PubMed1996

Focal liver lesions: fast T2-weighted MR imaging with half-Fourier rapid acquisition with relaxation enhancement.

PURPOSE: To compare the clinical usefulness of the half-Fourier rapid acquisition with relaxation enhancement (RARE) technique at T2-weighted magnetic resonance (MR) imaging of focal liver lesions with that of multishot RARE MR imaging and contrast material-enhanced helical computed tomography (CT). MATERIALS AND METHODS: Half-Fourier RARE and multishot RARE imaging and helical CT were performed in 48 patients with 102 focal liver lesions and in three patients with diffuse metastatic liver disease. Images were compared qualitatively and quantitatively for image quality, lesion conspicuity, and ability to help differentiate solid lesions from hemangiomas. RESULTS: All half-Fourier RARE images were free of respiratory artifact. In the 48 patients with 102 focal lesions, CT, half-Fourier RARE, and multishot RARE images depicted 101, 99, and 90 lesions (99%, 97%, and 88%), respectively. CT failed to depict focal lesions in one patient with diffuse metastatic liver disease. All techniques had high accuracy for distinction of hemangiomas from solid masses (areas under the receiver operating characteristic curves were between 0.96 and 0.99). CONCLUSION: Half-Fourier RARE MR imaging is a rapid and accurate technique for detection and characterization of focal liver lesions.

Adult↗
PubMed1996

Prolonged persistence of substantial volumes of potentially viable brain tissue after stroke: a correlative PET-CT study with voxel-based data analysis.

BACKGROUND AND PURPOSE: The existence in humans of brain tissue at risk for infarction but potentially viable (eg, the penumbra) remains unproven. One retrospective operational definition of such tissue includes its final infarction despite a relatively preserved or even normal cerebral metabolic rate of oxygen (CMRO2) in the early hours after stroke onset. Although previous positron emission tomography (PET) studies identified tissue whose CMRO2 declined from the acute to the subacute stage, in principle compatible with deteriorating penumbra, they all lacked a coregistered CT scan mapping of final infarct and an objective three-dimensional PET data analysis, while many patients were studied in the subacute (up to 48 hours) phase. We have evaluated whether tissue with CMRO2 ranging above a threshold for presumably irreversible damage in the first 18 hours of middle cerebral artery territory stroke, but below it in the chronic stage, could be retrospectively identified within the final infarct volume. METHODS: Our data bank comprises 30 consecutive patients with first-ever middle cerebral artery territory stroke prospectively studied with PET within the first 18 hours after clinical onset; the 15O equilibrium method was used to measure cerebral blood flow and CMRO2. All survivors with the following criteria were eligible for the present study: (1) technically adequate chronic-stage PET performed in the same stereotaxic conditions, (2) coregistered CT scan also performed in the chronic stage, and (3) an infarct of sufficient dimension (>16mm diameter) on late CT. Corresponding CT scan cuts and PET slices were exactly realigned, and the outlines of CT hypodensities were superimposed on the corresponding CMRO2 matrix. Infarcted voxels with CMRO2 values less than or greater than 1.40 mL/100 mL per minute (ie, the generally accepted threshold for irreversible damage) were automatically identified and projected on matrices of all other PET parameters and for both PET studies. RESULTS: Eight patients (mean age, 78 Years) were eligible for the present study. The acute-stage PET study was performed 7 to 17 hours after stroke onset and the chronic-stage PET 13 to 41 days later. Within the final infarct, mean CMRO2 fell significantly from the acute- to the chronic-stage PET study (P<.001). Eventually infarcted voxels with acute-stage CMRO2 values above the threshold were found in each of these eight patients; they were most often situated near the infarct borders and constituted 10% to 52% (mean, 32%) of the final infarct volume. The acute-stage CMRO2 in these voxels ranged up to 4.13 mL/100 mL per minute but fell below 1.40 mL/100 mL per minute in 93% of them at the chronic-stage PET. in 7 of 8 patients the acute-stage mean cerebral blood flow ranged from 10 to 22 mL/100 mL per minute, and the mean oxygen extraction fraction was markedly increased (>0.70) in these voxels, consistent with a penumbral state. CONCLUSION: In a strictly homogeneous sample of prospectively studied patients, we have identified, up to 17 hours after stroke onset, substantial volumes of tissue with CMRO2 well above the assumed threshold for viability that nevertheless spontaneously evolved toward necrosis. This tissue exhibited penumbral ranges of both cerebral blood flow and oxygen extraction fraction and thus could represent the part of penumbra that might be saved with appropriate therapy.

Aged↗
PubMed1996

Do changes in oxygen metabolism in the unaffected cerebral hemisphere underlie early neurological recovery after stroke? A positron emission tomography study.

BACKGROUND AND PURPOSE: Whether an initial depression of function in the unaffected hemisphere ("transcallosal diaschisis") plays a role in early neurological recovery after acute stroke remains controversial. Previous studies were confounded by lack of acute-stage assessment with follow-up and by the problem of defining a suitable control group, since preexisting stroke risk factors may influence prestroke cerebral metabolism. We evaluated with positron emission tomography (PET) the relationships between unaffected-hemisphere (ie, contralateral) oxygen consumption (cCMRO2) and quantitative neurological assessments (and their respective evolution over time) after ischemic stroke. METHODS: Among 30 consecutive patients with first-ever middle cerebral artery ischemic stroke studied with the (15)O equilibrium method, we selected all survivors (n=19; mean age, 74.6 years) who were investigated both within the first 18 hours after stroke onset (PET1; mean, 11 +/- 4 hours) and 15 to 30 days later (PET2; mean, 24 +/- 10 days), with each patient serving as his/her own control. Neurological deficits were quantified using Orgogozo's middle cerebral artery scale (N score) at each PET session. Neurological changes were calculated as changes in the N score. A late CT scan coregistered with PET provided infarct topography and volume index. RESULTS: At PET2, we observed the overall expected neurological recovery. There was a nearly significant trend for a decrease in cCMRO2 from PET1 to PET2, especially for the neocortex (P=.08, F test); in a subgroup of eight patients with large infarcts, this CMRO2 decline was significant (P<.05) in the mirror region to the infarct. There was no significant correlation (Spearman's tests) between acute-stage cCMRO2 and same-day N scores or between changes in cCMRO2 versus changes in N score from PET1 to PET2 (any region). There was a nearly significant trend for lower PET2 cCMRO2 in the subgroup of eight patients with large compared with small infarcts (P=.06). CONCLUSIONS: We found no evidence for an influence of cCMRO2 on acute-stage neurological deficit or for a role of the unaffected hemisphere in early recovery after acute MCA ischemic stroke. The decline in unaffected-hemisphere metabolism from the acute to the subacute stage in the face of overall clinical recovery appears clinically irrelevant. The fact that the neocortical cCMRO2 at PET2 tended to be lower, and declined significantly from PET1 to PET2 in the mirror region in the subgroup of patients with large infarcts, suggests that this delayed effect represents transcallosal fiber degeneration.

Aged↗
PubMed1996

Computer-assisted planning of oral implant surgery. An approach using virtual reality.

A planning system for oral implant surgery is described. This system allows the interactive placement and adjustment of models representing oral implants on CT volume data. These CT data can be shown as two-dimensional (2D) slices, or as a three-dimensional (3D) surface-rendered model. The viewpoint is fully adaptable, and stereoscopy results in an enhanced insight in the interrelation between implants and structures. This approach offers many advantages when compared with the traditional manual planning or with a 2D computer based planning. Clinical trials are being performed.

Computer Simulation↗
PubMed1995

Characterisation of intracranial aneurysms with MR angiography.

The purpose of this study was to compare the accuracy of 3D time-of-flight (TOF) acquisitions in the characterisation of intracranial aneurysms. Fourteen patients with aneurysms proven on intra-arterial angiography were first studied with a 3D TOF acquisition. When the aneurysms were incompletely demonstrated, additional MR angiography (MRA) acquisitions were performed, including black-blood MRA, 2D TOF, phase-contrast and contrast-enhanced TOF.3D TOF MRA was sufficient for detection of the aneurysm in 13 of 14 cases and characterisation of the aneurysm was possible in 6. All the initial shortcomings of the TOF technique could be analysed and explained by means of additional MRA techniques. This study suggests that the combination of different MRA techniques offers new possibilities for noninvasive investigation of intracranial aneurysms.

Adult↗
PubMed1995

Magnetic resonance angiography of supratentorial tumours: comparison with selective digital subtraction angiography.

We compared magnetic resonance angiography (MRA) and intra-arterial digital subtraction angiography (IADSA) in the study of brain tumours and assessed the utility of gadolinium-enhanced MRA. We studied 17 patients with supratentorial brain tumors. The entire brain was imaged with multiple overlapping thin volume acquisitions. After IV injection of gadolinium-DTPA, a single thick-slab MRA acquisition was performed. Standard three-dimensional (3D-TOF) acquisitions (in six patients) and 3D-TOF with magnetization transfer prepulse and tilted optimisation nonsaturing radiofrequency excitation pulses (in 11 patients) were used. Displacement of the anterior cerebral artery, main stem and insular branches of the middle cerebral artery was seen well on unenhanced and contrast-enhanced MRA. Displacement of the lenticulostriate and anterior choroidal arteries was seen only once, after Gadolinium. Tumour encasement of the middle cerebral artery was demonstrated in one patient. Tumour vessels were seen in 2 of 8 cases before and 3 of 8 after gadolinium; Tumour hypervascularity was seen only after gadolinium, in 3 of 8 cases. Study of the veins was possible only on gadolinium-enhanced MRA. Displacement of the venous angle was seen in 4 of 7 patients in the frontal, and in all of 8 patients on the lateral projections. Early venous drainage was not seen. Patency of the dural venous sinuses was demonstrated in all patients, but in one neoplastic occlusion of a cortical vein was recognized.

Adult↗
PubMed1995

Spiral CT of the temporal bone: value of image reconstruction at submillimetric table increments.

Axial spiral CT of the temporal bones with a nominal slice thickness of 1 mm and 180 degrees linear interpolation was performed in 13 patients. In 18 temporal bones, the spiral data set was used to reconstruct overlapping axial images with a table increment of 0.1 mm. These images gave additional information in four cases: in two by examining the heavily overlapping axial images themselves, and in two by obtaining supplementary information from secondary image reconstructions. In two cases less information was obtained than by using the conventional incremental images. This study shows that reconstructing overlapping slices can be useful, even if the temporal bone is scanned at 1 mm nominal slice thickness.

Humans↗
PubMed1995

A semiautomatic three-dimensional segmentation method for disarticulation of bone structures on spiral computed tomography images.

The use of binary thresholding for segmenting bone structures on spiral computed tomography images is negatively influenced by partial volume effects (PVEs) induced by the image acquisition. PVE leads to mixed voxels, making the binary decision "bone" or "nonbone" a difficult one to take. As a result, two distinct bone structures that are close to each other will often appear to be connected by this method. A typical example consists of "acetabulum/femural head" pairs in the pelvic region. To separate them, a clinical user must interactively draw a disarticulation line. This procedure is time consuming (often interaction in 50 slices is needed) and leads to unsmooth visualization of the disarticulated areas (by three-dimensional [3D] rendering techniques). We developed a semiautomatic cutting algorithm that leads to smooth disarticulated surfaces and considerably decreases the amount of user interaction. A sheet detection operator is applied to automatically separate bone structures. Detected sheets are used as disarticulation lines. Postprocessing ensures that sheets not relevant for the application do not influence the resulting image. Our approach is encapsulated in an interactive segmentation environment based on thresholding and 3D connected-component labeling. Results are shown for pelvic region, wrist, and foot bone disarticulations.

Algorithms↗
PubMed1995

Healthy aging, memory subsystems and regional cerebral oxygen consumption.

The present study was designed to search for concomitant age-related changes in memory subsystems, defined according to current structural theories, and resting oxygen consumption in selected brain regions. We have investigated a sample of subjects between 20 and 68 years of age and strictly screened for their good health. We applied in the same subjects a battery of neuropsychological tests selected to investigate several memory subsystems, and high-resolution positron imaging with stereotaxic localization to study a purposely limited number of cerebral structures, selected on a priori hypotheses to match the different memory subsystems. Our results showed significant age-related changes in performance on some tests, consistent with the literature, including an increase in semantic memory and a decrease in both working memory (central executive system) and verbal episodic and explicit memory. There was also an age-related linear decrease in global brain oxygen consumption which regionally reached statistical significance for the neocortical areas and the left thalamus. There was a limited number of significant, age-independent correlations between the raw psychometric test scores and resting regional oxidative metabolism. Consistent with our present understanding of the functional anatomy of memory, the Associate Learning scores (verbal episodic and explicit memory) were positively correlated with left hippocampal and thalamic metabolism. The positive relationships found between right hippocampal metabolism and performance in the Associate Learning and the Brown-Peterson tests were less expected but would be consistent with findings from recent PET activation studies. The results from this investigation are discussed in the light of current knowledge concerning the neuropsychology and the neurobiology of both aging and memory.

Adult↗
PubMed1995

Contribution of PET in the diagnosis of recurrent colorectal cancer: comparison with conventional imaging.

The clinical value of total body PET with FDG was evaluated in 76 patients presenting with or suspected of recurrent local or distant colorectal cancer. PET results were compared to those of routine imaging (CT pelvis, CT/US liver and CXR). The accuracy of PET for local disease was 95% which was superior to CT-pelvis (accuracy 65%). PET accuracy for liver metastases (98%) compared favourably to CT/US-liver accuracy (93%). Unexpected extra-hepatic mestastases were detected by PET in 14 locations in 10 patients. Also, a primary breast cancer was found in one patient. The main value of PET appeared an improved staging of apparently resectable, local or distant recurrent disease. Thereby, a more adequate indication of major secondary surgery could be attained.

Colorectal Neoplasms↗
PubMed1995

Effect of manganese dipyridoxal diphosphate on liver magnetic resonance imaging and serum bilirubin in rats with removable biliary obstruction.

RATIONALE AND OBJECTIVES: It is known that manganese dipyridoxal diphosphate (Mn-DPDP) causes persisting liver enhancement in cholestatic rats, that free Mn++ plus bilirubin induces intrahepatic cholestasis, and that free Mn++ is released in vivo after Mn-DPDP injection. Hence, there is a concern about potential secondary intrahepatic cholestasis in patients who have biliary obstruction. In this study, we further investigated this issue. METHODS: Removable total biliary obstruction (RTBO) was induced in 12 rats. Six of them (group A) received Mn-DPDP (25 mumol/kg). The others (group B) served as control animals. The data from serial magnetic resonance imaging and serum bilirubin tests were compared. RESULTS: Without Mn-DPDP, a minimal increase of the liver intensity was observed in both groups because of cholestasis. In group A, the intensity of the liver was strongly enhanced with Mn-DPDP but normalized within 48 hr after removal of the obstruction. In both groups, total bilirubin levels increased up to 131.67 mumol/l 2 days after RTBO but rapidly decreased within 4 hr and almost normalized within 24 hr after removal of the obstruction, suggesting a lack of Mn-DPDP influence on the bilirubin level. CONCLUSION: We found that Mn-DPDP did not cause secondary intrahepatic cholestasis. Retained Mn++ is likely eliminated after restoration of bile flow. These results indicate that Mn-DPDP can be used in patients who have obstructive jaundice as long as it is followed by successful bile drainage.

Animals↗
PubMed1995

Localization of metalloporphyrin-induced "specific" enhancement in experimental liver tumors: comparison of magnetic resonance imaging, microangiographic, and histologic findings.

RATIONALE AND OBJECTIVES: We investigated the tumor specificity of gadolinium mesoporphyrin (Gd-MP) and manganese tetraphenylporphyrin (Mn-TPP) as magnetic resonance (MR) imaging contrast agents. METHODS: Fifteen rats with multiple hepatocellular carcinomas and eight rats with implanted Novikoff hepatomas were given intravenous injections of either Gd-MP or Mn-TPP at 0.05 mmol/kg, which was compared with nonspecific gadopentetate dimeglumine (0.3 mmol/kg). T1-weighted spin-echo images were obtained before and up to 48 hr after injection and compared with corresponding microangiograms and histologic specimens. The relative enhancement of organs and tumors was plotted as a function of time. RESULTS: Initially, both metalloporphyrins behaved as nonspecific agents, similar to gadopentetate dimeglumine, and enhanced the tumor by perfusion and diffusion. However, metalloporphyrins, but not gadopentetate dimeglumine, caused a delayed (> or = 3 hr) enhancement in some compartments of certain lesions. The MR imaging-microangiography-histology matching technique revealed that those compartments were actually nonviable components, including necrosis (n = 10), thrombosis (n = 7), and cystic secretion (n = 3), but not viable tumor tissue. CONCLUSION: Metalloporphyrins did not prove to be tumor specific. However, the observed affinity for nonviable tissue has elicited other potential applications for these agents.

Angiography↗