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Biomedical subjects

N Grenier

Publications and source records attributed to N Grenier.

At least 73 records · Page 4Linked to original sources
PubMed1995

USPIO-enhanced MR imaging of glycerol-induced acute renal failure in the rabbit.

Enhanced-MR imaging in combination with ultrasmall superparamagnetic iron oxide (USPIO) was used in the glycerol-induced model of acute renal failure (ARF) in the rabbit to detect renal perfusion abnormalities. A control group (n = 5) and an ARF group (n = 5) were studied after intramuscular injection of glycerol (10 ml/kg) with T2-weighted spin-echo sequence at 1.5 T and a 27 mumol/kg IV dose of iron. The signal intensity (SI) was quantified in the cortex, the outer medulla (OM), and the inner medulla (IM). In control rabbits, the maximum SI decrease after USPIO injection was in the OM (76% +/- 3.6), as this is the region of maximal vascular density, then in the IM (73.4% +/- 2.9). In the glycerol group, SI loss in the OM (61% +/- 12.6) and the IM (45.2% +/- 16.24) was significant less than in the control group (p < .05). Pathology results showed fibrinous thrombus in the efferent arterioles and congestive aspect of the vasa recta in the medulla. We argue that a reduced medullary concentration of USPIO in the renal failure group is indicative of medullary hypoperfusion.

Acute Kidney Injury↗
PubMed1995

Evaluation of experimentally induced renal hypoperfusion using iron oxide particles and fast magnetic resonance imaging.

RATIONALE AND OBJECTIVES: Renal perfusion can be evaluated with first-pass study of superparamagnetic iron oxide particles (SPIO). We applied this technique to a unilateral renal hypoperfusion model in rabbits. METHODS: Turbo fast low-angle shot sequences (acquisition time = 440 msec), after bolus injection of SPIO (100-140 mumol/kg iron), were performed in two control groups (n = 5 in each) and one group (n = 5) with a left renal blood flow reduction caused by a surgical interrenal aortic ligature (140 mumol/kg iron). Qualitative and quantitative analysis using relative blood volume (rRBV), relative blood flow (rRBF), and mean transit time (MTT) were performed. RESULTS: Signal changes were symmetric in control groups without significant differences between the kidneys. The experimental group showed a significantly delayed and less pronounced maximal reduction of signal related to a significantly decreased rRBF and increased rRBV and MTT in the left kidney (p < .05). CONCLUSION: This study shows the effectiveness of a dynamic magnetic resonance study using SPIO to detect unilateral kidney perfusion reduction.

Animals↗
PubMed1995

[Exploration of renal arteries by angio-MRI].

Major clinical challenges are involved in applications of MR-angiography for the study of renal arteries, mostly for the diagnosis of renovascular hypertension. This technique now competes with color Doppler flow sonography and spiral CT. MR angiography of the renal arteries can be performed with 2D or 3D, flight-time or phase contrast sequences. Main and co-dominant arteries are usual by visualized on all sequences, but small accessory arteries are often missed. The diagnosis of stenosis is based on the presence of an area of signal extinction. The degree of extinction depends on the degree of turbulence, the type of technique, the length of TE and spatial resolution parameters, which is why scoring of stenoses is difficult and frequently overestimated. The diagnostic performance for stenosis is between 50 and 100% for sensitivity and between 80 and 97% for specificity. Detection of distal stenoses is poor because of respiratory artifacts. Multiphase acquisitions make it possible to measure the renal blood flow on each renal artery, adding hemodynamic criteria to this diagnosis.

Humans↗
PubMed1995

[Functional study of Swanson's metacarpophalangeal arthroplasties in rheumatoid arthritis].

To validate a functional hand evaluation and to obtain an historical control group in a project of metacarpophalangeal total joint prosthesis, we reviewed our experience over a ten year period of Swanson's metacarpophalangeal joint arthroplasty in rheumatoid arthritis. Forty-nine implants in fourteen rheumatoid arthritis patients were reviewed clinically, radiologically and evaluated by the Arthritic Hand Function Test. The mean follow up was 4.5 years. All patients were ready to repeat the experience except one. The mean metacarpophalangeal joint range of motion was 37 degrees (18 degrees to 55 degrees) with a mean of 7 degrees ulnar deviation. Although their functional performance was 50% of normal, all patients completed the test. The strength was generally greater on the operated side. The low complication rate (6% fracture rate) with the successful functional outcome of Swanson's metacarpophalangeal joint arthroplasty in rheumatoid arthritis will be the gold standard for any new implant to develop.

Adult↗
PubMed1995

[Thromboembolism and ovarian hyperstimulation].

Three new cases of thromboembolic accidents involving the superior vena cave were associated with ovarian hyperstimulation and multiple pregnancy. On the basis of a review of the literature, three syndromes were individualized. First embolic arteries are infrequent and serious with an important morbidity; low doses of gonadotrophines is sufficient for causing this pathology. Second, thrombosis of the superior vena cava is late, during in vitro fertilization regimens with GnRH analogs complicated with serious hyperstimulation (degree III). Third, pregnancy is always present; pulmonary complications are very uncommon. Thrombosis of inferior vena cava is late, pregnancy is often present but women are frequently at risk of thromboembolic accident. Prevention of hyperstimulation is important. When present, HBPM is recommended for prevention of thromboembolism. Diagnostic of thrombosis is made with clinical examination and morphologic complementary exams such colour-vascular Doppler and magnetic resonance imaging. Curative treatment requires heparinization.

Adult↗
PubMed1994

Evaluation of intrarenal distribution of ultrasmall superparamagnetic iron oxide particles by magnetic resonance imaging and modification by furosemide and water restriction.

RATIONALE AND OBJECTIVES: The steady-state intrarenal distribution of ultrasmall superparamagnetic iron oxide (USPIO) particles in the cortex, the outer medulla (OM), and the inner medulla (IM) was investigated using magnetic resonance imaging in the normal rabbit kidney and in situations that modify the corticopapillary osmotic gradient. METHODS: Experiments were performed on rabbit kidneys with T2-weighed spin-echo sequence and T2-weighted gradient-recalled-echo sequence. The intravenous dose was 27 mumole/kg of iron in all rabbits. Three groups were studied: normally hydrated rabbits (n = 5), after water restriction (n = 5) to increase the osmotic gradient, and after furosemide injection (n = 5) to decrease the osmotic gradient. The signal intensity (SI) was quantified by region of interest placed on the cortex, the OM and the IM. RESULTS: In normally hydrated rabbits, a maximal decrease of the SI after USPIO was noted in the medulla, without significant difference between the OM and the IM on spin-echo sequences. The decrease of the SI was maximal in the IM on gradient-recalled echo sequences. In dehydrated animals, the maximum SI loss was in the OM. The furosemide-induced transient enhancement of the IM lasted a few minutes. CONCLUSIONS: The observed SI changes due to the distribution of the USPIO between OM and IM were not based on modifications of the osmotic gradient. The authors suggest that these SI changes were mostly dependent on the vascular density.

Animals↗
PubMed1994

[Comparison of different monitoring techniques for vascular access in chronic hemodialysis].

Aim of the study was to compare different techniques of monitoring for vascular accesses in our chronic hemodialysis patients. Twenty seven patients (14 men, 13 women) were investigated. The accesses studied consisted of 19 arteriovenous fistulas and 8 vascular protheses. Twenty-four were trouble free, venous pressure was high in two, one was difficult to puncture. Three measurements of recirculation percentage were made for each patient, as well as a color Doppler flow imaging, and a digital angiography of the access. Recirculation measurements were normal for all patients including those with functional abnormalities. A stenosis was found 9 times with the Doppler and 10 times by angiography, there being disagreement between the two techniques in one case. The location of the stenosis was the same in the 9 concordant cases. There was a very strong correlation between the degree of stenosis found using the two techniques (p < 0.0001). In conclusion, measurement of recirculation appears to us to be of no interest for verifying a vascular access. On the other hand, the color Doppler seems to be an excellent choice for detecting an abnormality. An arteriographic confirmation seems necessary before correction.

Adolescent↗
PubMed1994

[Imaging of the renal transplant. Radiological methods].

Ultrasound examination with morphological sonography and color flow imaging is now considered as the main technique for the follow-up of renal transplants. Morphology of the graft, and quality of perfusion can be assessed non invasively with this technique. Indications of IV pyelography decreased considerably in many centers. CT can help in characterizing intra-abdominal collections. MR will probably play a major role in the future allowing the graft itself, the perirenal space, and the intrarenal vessels to be studied by means of MR-angiography techniques.

Diagnostic Imaging↗
PubMed1991

Study of correlation between intradiscal pressure and magnetic resonance imaging data in evaluation of disc degeneration. Therapeutic issue with percutaneous nucleotomy.

Intradiscal pressure and volume measurements using discomanometry were correlated to features of degeneration noted with magnetic resonance (MR) imaging in 36 discs in patients scheduled for percutaneous nucleotomy. Discomanometric data (intradiscal pressure and degree of pressure loss at 0 and 60 seconds after intradiscal infusion, area under the pressure curve, and discal volume) were not correlated with the MR data (degree of disc height loss and degree of signal intensity loss on T2-weighted images). Results of nucleotomy were strongly correlated with discomanometric data but not with the studied MR factors. Discomanometry by evaluating the physical status of discs, may predict results of percutaneous nucleotomy and consequently play a major role in patients selection.

Female↗
PubMed1991

In vivo and ex vivo magnetic resonance imaging evaluation of early disc degeneration with histopathologic correlation.

The in vivo and ex vivo microanatomic appearance of early disc degeneration were identified by magnetic resonance imaging and correlated with their respective histopathologic findings. Five cadaver spines (18 discs) and 25 patient studies (122 discs) all imaged at 1.5 Tesla were studied. Two signs of early degenerative disc disease were found: infolding and the central dot. Infolding of the central fibers of the outer annulus coalesced into a central dot of low signal intensity that was seen on both the ex vivo and in vivo images. Infolding was seen 29 of 122 times, and the central dot was observed 15 to 122 times on the in vivo images. A later form of degenerative disc disease was identified as a separation of the nucleus pulposus from the hyaline cartilage end-plate. This separation was seen as a linear area of either low or high signal intensity on the ex vivo images but only as a band of high signal intensity on the in vivo spin-echo 2,500-msec/80-msec images. Only 7 of 122 in vivo discs showed this separation. Internal herniation of nucleus pulposus into the outer annulus was seen only on the ex vivo images. Early degenerative disc disease may exist before there is loss of disc height or signal intensity on the long time-to-repetition (TR)/time-to-echo (TE) magnetic resonance images.

Adult↗
PubMed1991

Detection of vascular complications in renal allografts with color Doppler flow imaging.

One hundred ninety-five color Doppler flow (CDF) examinations were performed in 146 renal allografts to assess the capabilities of this technique in detecting intra- or extrarenal vascular complications. Conventional angiography was also performed in 44 transplants. In the group of transplants with angiographic correlation, CDF sonography enabled correct identification of 30 of 34 vascular complications. CDF showed 10 of 11 significant stenoses of the renal artery or of one of its main branches. There were two false-positive renal artery stenoses (one normal artery and one 40% stenosis). Nine of nine renal artery thromboses and the single pseudoaneurysm were also identified. Within the parenchyma, CDF sonography demonstrated five of five segmental infarcts, two of two postbiopsy arteriovenous fistulas, and three of six segmental or interlobar artery stenoses. Measurement of peak systolic velocity showed a significant difference (P less than .05) between a group (n = 8) with significant stenosis of the renal artery or one of its main branches (mean, 215.2 cm/sec +/- 32) and a group (n = 14) without stenosis (mean, 99.2 cm/sec +/- 19).

Adult↗
PubMed1991

Hemodialysis grafts: color Doppler flow imaging correlated with digital subtraction angiography and functional status.

Twenty-two patients with hemodialysis grafts were prospectively evaluated with color Doppler flow imaging and digital subtraction angiography (DSA). Eighteen patients had normal functional parameters during hemodialysis, and four had increased venous pressure during hemodialysis. Color Doppler flow imaging allowed identification of nine macroaneurysms related to wall degeneration, two cases of spontaneous fistula formation between the graft and peripheral veins, and 20 stenoses. Use of color Doppler flow imaging led to overestimation of the degree of stenosis at the venous anastomosis when compared with use of angiography. Three cases of subclavian venous stenosis were identified only at angiography. Color Doppler flow imaging appears accurate in the detection of stenoses and seems sufficient for follow-up of normally functioning grafts. However, because of its low sensitivity for identification of proximal stenoses and the necessity of obtaining an angiogram to plan surgical or percutaneous correction, DSA remains the technique of choice.

Angiography, Digital Subtraction↗
PubMed1991

Normal and degenerated intervertebral disk: in vivo and in vitro MR imaging with histopathologic correlation.

The components of the intervertebral disk serve two purposes. The hydrophilic matrix is contained by circumferential rings of fibrocartilage (outer anulus) and Sharpey's fibers. The gellike hydrophilic matrix acts as a cushion between the vertebral body endplates by providing an even distribution of axial and rotational compressive forces. The construction and integrity of the intervertebral disk are assessed well by MR. The purpose of this pictorial essay is to show the in vitro and in vivo MR appearances of the normal and degenerated disk, and to correlate these MR changes with their respective histopathologic findings.

Humans↗
PubMed1991

[Foraminal lumbar hernia. Diagnostic and therapeutic aspects (apropos of 40 cases)].

This study was based upon a retrospective analysis of 40 case-histories of foraminal lombar disc herniations. Patients presented an isolated femoral neuralgia 3 times out of 4, were males twice out of 3 and were about fifty. Computed Tomographic Scanning oriented precisely the diagnosis for half the cases but only suggested it for the other 50 per cent. Computed Tomographic Scanning of lumbar discography was executed 5 times and confirmed the foraminal lumbar disc herniation. MRI executed 18 times confirmed the foraminal lumbar disc herniation by sagittal, axial and frontal-oblique views. 7 patients recovered with medical treatment. 4 patients with a subligamentous lumbar disc herniation recovered with percutaneous treatment. 29 patients underwent surgical treatment. The classical intervertebral foramina approach by complete facetectomy and arthrodesis was replaced by more conservative technics regarding bony structures: extraforaminal lumbar disc herniation was removed by paraspinal approach, whereas foraminal lumbar disc herniation was removed by a combined approach associating an interlaminar approach with a paraspinal one.

Adult↗
PubMed1990

Osteoid osteoma of the cervical spine. Misleading MR features about a case involving the uncinate process.

The authors studied the usefulness of MR imaging in the diagnosis of an osteoid osteoma occurring within the C4 left uncinate process. It was detected by scintigraphy and diagnosed by CT. On T2-weighted MR images the nidus showed a very low signal intensity with an increased signal within the adjacent end-plates. This pattern was misleading and more suggestive of degenerative disk disease.

Adult↗