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Biomedical subjects

P Douek

Publications and source records attributed to P Douek.

35 records · Page 2Linked to original sources
PubMed1993

Is water diffusion restricted in human brain white matter? An echo-planar NMR imaging study.

Water diffusion is extremely anisotropic in brain white matter, depending on myelin fiber orientation. A suggested, but unproven cause of anisotropy is that, in the direction transverse to the myelin fibers, axonal water diffusion is prevented by the presence of the myelin sheath. We found, however, using an ultra-fast nuclear magnetic resonance imaging technique, that the dependence of the diffusion coefficient on the diffusion time does not support the model of water restriction by impenetrable barriers. These results, which were obtained non-invasively in vivo in the human brain, imply that water diffuses with a measurable rate across myelin fibers.

Body Water↗
PubMed1993

[Intravascular echographic imaging: experimental validations and limits. An in vitro study].

Intravascular ultrasound is a new method of visualizing details of vascular pathology, providing (real time) high resolution images of vascular walls. Most of the research on the technique has explored its qualitative and quantitative capabilities to improve the assessment of atherosclerotic vascular disease in vivo. Intravascular ultrasound differs from angiography and angioscopy in its ability to penetrate below the surface of the vessel lumen, demonstrating specific appearances of the distribution and composition of plaque. Image analysis is operator dependent. Although this technology is very promising limitations such as artefacts and loss of image quality in heavily calcified vessels hinder its use. There is hope that this imaging technique may ultimately improve the results of endovascular interventions.

Arteries↗
PubMed1993

Diffusion and perfusion magnetic resonance imaging in brain tumors.

The article reviews recent progress made in the field of diffusion and perfusion magnetic resonance (MR) imaging and presents possible applications in brain tumors. Diffusion, a new parameter, provides useful data to assess tissue structure and function. Perfusion MR imaging gives results that are somewhat similar to those obtained with classic non-MR imaging methods, but it offers several potential advantages.

Brain Neoplasms↗
PubMed1992

Target lesion calcification in coronary artery disease: an intravascular ultrasound study.

OBJECTIVES: The purpose of this study was to evaluate the frequency, amount and distribution of target lesion calcification in patients undergoing transcatheter therapy for symptomatic coronary artery disease. BACKGROUND: Coronary artery target lesion calcification may be an important determinant of response to transcatheter therapy: balloon angioplasty causes dissections in calcified lesions, directional atherectomy cuts calcium poorly, rotational atherectomy causes preferential ablation of calcium and laser irradiation effect may vary. Intravascular ultrasound imaging is a highly sensitive technique for detection of plaque calcification in vivo. METHODS: We performed intravascular ultrasound imaging before or after, or both, various transcatheter therapies in 110 patients. These 84 men and 26 women had a mean age of 60 years and a duration of angina of 22 +/- 34 months. Forty-nine patients had one-vessel, 29 had two-vessel, 25 had three-vessel and 7 had left main coronary disease. Vessels treated and imaged were the left main (n = 7), left anterior descending (n = 47), left circumflex (n = 18) and right (n = 38) coronary arteries. RESULTS: Eighty-four patients (76%) had target lesion calcification; 29 patients had one-quadrant, 25 had two-quadrant, 17 had three-quadrant and 13 had four-quadrant calcification. The calcification was superficial in 42 patients, deep in 13 and both superficial and deep in 31. The axial length of calcium could be measured in 29 patients; it was < or = 5 mm in 11 and > or = 6 mm in 18. Fluoroscopy detected calcification in 50 patients (48%, p < 0.001 vs. detection by ultrasound); this proportion increased to 74% in patients with calcification of two or more quadrants and to 86% in patients with calcification > or = 6 mm in length of two or more quadrants. Calcification was more common in patients who smoked and tended to be more common in patients with multivessel disease or previous coronary artery bypass graft surgery. CONCLUSIONS: We conclude that target lesion calcification occurs in 75% of patients with symptomatic coronary artery disease requiring angioplasty. Target lesion calcification is best detected, localized and quantified by intravascular ultrasound. These observations may be important in selecting devices for transcatheter therapy.

Adult↗
PubMed1992

Value of CT and sonography in the conservative management of acute splenoportal and superior mesenteric venous thrombosis.

Acute splenoportal and superior mesenteric venous thrombosis were diagnosed on sonography and computed tomography (CT) in six patients. Sonography demonstrated the presence of echoic material filling the involved vessels in all patients. Precontrast CT scans demonstrated an increased, intra luminal density of the clots in four patients with splenoportal thrombosis. However, in two cases of superior mesenteric venous thrombosis, no hyperdensity was observed within the lumens. Nevertheless, the clots were always visualized as low-density regions in the vessel lumens after bolus injection. Intravenous anticoagulant therapy was started immediately after the diagnosis. All patients were evaluated twice a week with sonography and/or CT until recanalization occurred. The patency of the previously involved vessels was assessed from 6 days to 4 weeks after the acute episode (average time of recanalization: 17 days) without development of collateral pathways. It is concluded that, in the absence of clinical signs of a life-threatening process, a conservative management of acute splanchnic thrombosis can be successfully achieved by (1) early diagnosis, (2) efficacious intravenous anticoagulant therapy, (3) careful imaging follow-up of these patients by sonography and/or CT during the acute phase and, finally, (4) by an extensive search for a hypercoagulable state.

Acenocoumarol↗
PubMed1992

Atherosclerotic saphenous vein grafts treated with different interventional procedures assessed by intravascular ultrasound.

Intravascular ultrasound imaging of saphenous vein grafts may enhance the angiographic interpretation of results following transcatheter interventions. We used intravascular ultrasound to study 18 patients with stenotic vein grafts following balloon angioplasty, atherectomy, or stent placement. In real-time imaging the three-layer appearance was rarely seen, calcification was infrequent (11% of patients), and atheroma were usually mildly echogenic ("soft"). Despite excellent angiographic results (reduction in percent diameter stenosis from 90 +/- 8% to 17 +/- 8%) and concordant improvement in lumen area by ultrasound regardless of the intervention, there was usually significant retained atheroma at the treatment site. Following balloon angioplasty, ultrasound showed multiple superficial fissures and fractures without discrete dissections. Atherectomy caused a smooth lumen surface without deep dissections or resections, but significant retained atheroma was observed with each one of the atherectomy procedures. Endovascular stents were concentric in the vein with reflective struts above compressed atheroma and an outer echogenic adventitia. Stent expansion was asymmetric axially and longitudinally and evidence of stent recoil was present. Thus intravascular ultrasound may be an important adjunct to angiography in characterizing postintervention results in saphenous vein grafts.

Aged↗
PubMed1992

Diffusion MR imaging: clinical applications.

Water self-diffusion, a recently discovered source of contrast on MR images, has already shown promise for some clinical applications. Most studies have been of the brain, essentially for technical reasons. Diffusion is useful in distinguishing the different components of brain tumors (cystic regions, edema, necrosis) from the tumor core itself. Recent studies have shown that diffusion is anisotropic in brain white matter (i.e., dependent on the fiber tract's orientation in space), offering new insights into myelin disorders. Diffusion is also dramatically altered in the minutes following ischemic injury in the cat brain, which may have tremendous impact for the diagnosis and management of hyperacute stroke. With ultrafast acquisition schemes, diffusion imaging has also been used outside the CNS, for instance, in the eye and kidney. Future applications include diffusion-localized spectroscopy and temperature imaging. This article reviews recent progress in this field and suggests potential applications.

Body Water↗
PubMed1990

[Spontaneous remission of renal artery stenosis in Takayasu's disease].

The authors report about one rare case of spontaneous subsidence of tight stenosis of the left renal artery in Takayashu's disease, which was followed up on two angiograms taken with an 11-year time interval. Knowing such evolution patterns may influence the treatment of such stenoses.

Adult↗
PubMed1986

[2 cases of coronary embolism. Angiographic diagnosis and anatomopathological confirmation].

The authors report two cases selected from a series of 61 cases of coronary embolism observed over an 18 year period at the Cardiovascular Hospital (Lyon) out of 4,860 autopsies of adult patients who died of cardiovascular causes. These two cases underwent coronary angiography, the results of which correlated with the autopsy findings. The authors review the causes and clinical manifestations of coronary embolism and compare their results with previously reported data, to establish the radiological features of coronary embolism. They notice the regular appearance of obstruction due to embolism and underline the importance of the associated negative signs (normality of the rest of the coronary circulation, absence of collateral vessels...) which makes the angiographic diagnosis one of elimination.

Adult↗
PubMedDate not supplied

Influence of bolus volume and dose of gadolinium chelate for first-pass myocardial perfusion MR imaging studies.

First-pass MR myocardial perfusion measurements require a well-defined left ventricular (LV) blood pool input function. We used a peripheral intravenous (i.v.) injection of a gadolinium (Gd) chelate to obtain a well-characterized LV time-intensity curve. Using a strongly T1-weighted subsecond MR sequence, we performed cardiac MR imaging after administering an IV bolus injection of one of three different doses of the Gd chelate: a standard dose (0.1 mmol/kg, group I, n = 8); a low dose with two bolus volumes (0.01 mmol/kg, 1/10e bolus volume, group II, n = 7, and 0.01 mmol/kg diluted in saline, same bolus volume as group I, group III, n = 3); and an intermediate dose (0.05 mmol/kg, group IV, n = 5). Unlike in group I (high dose), in groups II and III (low dose), the LV curve had a well-defined first peak, followed by a downslope and a recirculation peak. With the intermediate dose (group IV), a saturation effect still remained on the LV curve. The signal intensity (SI) enhancement of the myocardium was respectively 580 +/- 77% at 0.1 mmol/kg, 362 +/- 95% at 0.05 mmol/kg, and at 0.01 mmol/kg, it was 184 +/- 33% in group II and 272 +/- 8% in group III. In conclusion, with subsecond T1-weighted MR imaging and a low dose of Gd chelate (i.e., 0.01 mmol/kg), the LV input function is a well-defined first step for MR perfusion modeling.

Contrast Media↗
PubMedDate not supplied

Magnetic resonance imaging evaluation of the ascending aorta after graft-inclusion surgery: comparison between an ultrafast contrast-enhanced MR sequence and conventional cine-MRI.

The aim of this study was to compare the value of two magnitude-based MR sequences, a contrast-enhanced ultrafast MR sequence and a cine MR sequence, for the detection of flow around the graft in the postoperative ascending thoracic aorta. Thirteen patients who underwent ascending aortic surgery for dissection (n = 11) and aneurysm (n = 2) were enrolled. They were referred to MRI for mediastinum enlargement on the chest x-ray or mediastinal symptoms. All patients had replacement of the diseased ascending aorta using a graft-inclusion technique (with wrapping of the native aorta over the graft). Delays between surgery and MRI ranged from 15 days to 8 years (mean: 10 months). All patients were examined using a T1-weighted spin-echo sequence, a magnitude-based cine gradient-echo sequence, and an ultrafast contrast-enhanced MR sequence. MR images of the cine and the contrast-enhanced sequences were retrospectively and independently analyzed by two qualified radiologists for evidence of flow or thrombus around the graft, including perigraft structure and aneurysmal formations. Evidence of flow was detected by both methods in all aneurysmal formations of the ascending aorta located at suture level (n = 6). Evidence of flow in the perigraft structure was found in seven cases by contrast-enhanced MR sequence and in only four cases by cine MR sequence. Contrast-enhanced ultrafast MR sequence could be proposed as a minimally invasive and fast modality for assessing the perigraft structure, in graft-inclusion surgical procedures of the ascending aorta, when noncontrast enhanced MR sequences do not exclude the possibility of flowing blood in this structure.

Adult↗
PubMedDate not supplied

MR angiography: noninvasive vascular imaging of the abdomen.

Magnetic resonance angiography (MRA) has been used to image abdominal vessels less frequently than renal arteries. Until the use of fast contrast-enhanced (CE) techniques, an important limitation was the acquisition time of phase-contrast or time-of-flight imaging and, consequently, the creation of motion artifacts. Recent advances in MRA technology have shortened acquisition times, so it is now possible to obtain successive images in the arterial and then the portal phase. MRA can be used as an adjunct to any MR examination to assess, e.g., the arterial feeding of hepatocellular carcinoma, the encasement of arteries, and segmental portal thrombosis in pancreatic carcinoma. However, MRA has been used mainly to study chronic mesenteric ischemia, portal vein diseases, and complications from liver transplantation. The portal venous system is exquisitely portrayed with this method; MRA is as accurate as digital subtraction angiography (DSA) in the diagnosis of portal vein diseases. Acute mesenteric ischemia is an emergency in which computed tomography is the most appropriate imaging modality. Conversely, chronic mesenteric ischemia is best examined with CE-MRA, which is almost as accurate as DSA. CE-MRA is superior to DSA for the simultaneous exploration of the aorta, renal arteries, and iliac arteries, thereby providing a panoramic view of abdominal vascular involvement. MRA can be coupled with measurements of flow. With this functional approach, MRA is the only modality that can completely assess vascular diseases of the abdomen.

Abdomen↗
PubMedDate not supplied

Clinical assessment of a new stereoscopic digital angiography system.

PURPOSE: To assess the clinical feasibility of an experimental modified angiographic system capable of real-time digital stereofluoroscopy and stereography in X-ray angiography, using a twin-focus tube and a stereoscopic monitor. METHODS: We report the experience obtained in 37 patients with a well-documented examination. The patients were examined for coronary angiography (11 cases), aortography (7 cases), pulmonary angiography (6 cases), inferior vena cava filter placement (2 cases), and cerebral angiography (11 cases). Six radiologists were asked to use stereoscopic features for fluoroscopy and angiography. A questionnaire was designed to record their subjective evaluation of stereoscopic image quality, ergonomics of the system, and its medical interest. RESULTS: Stereofluoroscopy was successfully used in 25 of 37 cases; diplopia and/or ghost images were reported in 6 cases. It was helpful for aortic catheterization in 10 cases and for selective catheterization in 5 cases. In stereoangiography, depth was easily and accurately perceived in 27 of 37 cases; diplopia and/or ghost images were reported in 4 cases. A certain gain in the three-dimensional evaluation of the anatomy and relation between vessels and lesions was noted. As regards ergonomic considerations, polarized spectacles were not considered cumbersome. Visual fatigue and additional work were variously reported. Stereoshift tuning before X-ray acquisition was not judged to be a limiting factor. CONCLUSION: A twin-focus X-ray tube and a polarized shutter for stereoscopic display allowed effective real-time three-dimensional perception of angiographic images. Our clinical study suggests no clear medical interest for diagnostic examinations, but the field of interventional radiology needs to be investigated.

Adult↗
PubMedDate not supplied

MR color mapping of myelin fiber orientation.

Diffusion of water in brain white matter has been shown to be anisotropic: Water mobility is lower when measured perpendicular to the fiber direction rather than parallel to it. This feature was used to produce images of the myelin fiber orientation. Coronal and sagittal MR diffusion images were obtained in volunteers using an echo-planar imaging sequence sensitized to molecular diffusion in perpendicular directions. Color-coded images of myelin orientation were then generated by combining these images together. The orientation of the white matter tracts was found to be in excellent agreement with known anatomy. Myelin fiber orientation mapping may offer a new perspective to evaluate white matter disorders.

Algorithms↗
PubMedDate not supplied

Small nodule detection in cirrhotic livers: evaluation with US, spiral CT, and MRI and correlation with pathologic examination of explanted liver.

PURPOSE: The purpose of this work was to evaluate the detection and characterization of nodules > or = 8 mm and small hepatocellular carcinomas (HCCs) in liver cirrhosis. METHOD: Pathologic examination and results of US, helical CT, and dynamic MRI with gadolinium were compared after orthotopic liver transplantation (OLT) of 43 cirrhotic patients. Nodules were classified as macroregenerative nodules (MRNs), borderline nodules (BNs), and HCC. RESULTS: Pathologic examination classified 69 nodules: 50 MRNs, 6 BNs, and 13 HCCs. Sensitivities of MRN, BN, and HCC detection were, respectively, for US imaging 2% (1/50), 33.3% (2/6), and 46.2% (6/13); for helical CT 2% (1/50), 50% (3/6), and 53.8% (7/13); and for MRI 42% (21/50), 50% (3/6), and 76.9% (10/13). MRI detected 21 MRNs. They presented on T1/T2-weighted images as hyperintense/hypointense (n = 8), hyperintense/isointense (n = 7), hypointense/hypointense (n = 4), hypointense/isointense (n = 1), and hypointense depicted only on echo planar imaging (n = 1). The three detected BNs were hyperintense/hypointense nodules. The 10 detected HCCs appeared hyperintense/isointense (n = 7), hyperintense/hypointense (n = 2), and hypointense/isointense (n = 1). None of the MRNs but eight HCCs and one BN were enhanced after gadolinium injection. CONCLUSION: Contrast-enhanced MRI is the most sensitive technique for detecting liver nodules. No MR signal intensity pattern characteristic of small HCCs enables differentiation from benign nodules, however. Gadolinium enhancement is the most sensitive and specific characteristic of HCC.

Adult↗