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Biomedical subjects

C Douws

Publications and source records attributed to C Douws.

16 recordsLinked to original sources
PubMed1999

Volume flow measurement in hemodialysis shunts using time-domain correlation.

Volume flow was measured in 58 hemodialysis shunts (32 grafts and 26 radial fistulas) using the color velocity imaging-quantification method. This method is based on time-domain correlation for velocity calculation and integration of time-varying velocity profiles generated by M-mode sampling. Measurements were made in the brachial artery to estimate radial fistula flow or directly in the grafts. Intraoperator reproducibility was 14.9% for fistulas and 11.6% for grafts. Flow rate was significantly lower in abnormal shunts associated with a functional disorder or a morphologic complication (808 ml/min +/- 484) than in shunts associated with no abnormalities (1401 ml/min +/- 562). Receiver operating characteristic curves showed that a flow rate of 900 ml/min for fistulas and 1300 ml/min for grafts provided 81% and 79% sensitivity and 79% and 67% specificity, respectively. A functional disorder or a morphologic complication was associated with all fistulas and grafts in which flow rates were lower than 500 ml/min and 800 ml/min, respectively.

Adolescent↗
PubMed1996

Diagnosis of renovascular hypertension: feasibility of captopril-sensitized dynamic MR imaging and comparison with captopril scintigraphy.

OBJECTIVE: Angiotensin-converting enzyme inhibitors may decrease glomerular filtration rate when a significant renal artery stenosis is present. The purpose of this preliminary study is to evaluate the feasibility of captopril-sensitized, dynamic MR imaging of the kidney in a series of patients with a high suspicion of renovascular hypertension and to compare the results with those of captopril scintigraphy. SUBJECTS AND METHODS: Fifteen hypertensive patients with renal artery stenosis shown by angiography were studied with sequential gadolinium-enhanced MR imaging after oral administration of 50 mg of captopril, an inhibitor of angiotensin-converting enzyme. Symmetry of onset and evolution of tubular phases between the two kidneys were analyzed, and medullary signal intensity time curves were drawn for each kidney. When asymmetry between kidneys was noted, the same dynamic study was repeated 24 hr later, without captopril sensitization. All patients also underwent renal scintigraphy after administration of captopril to compare captopril-induced changes in both techniques. Three-dimensional time-of-flight MR angiography was also performed on all patients. RESULTS: MR imaging with normal and symmetric tubular phases showed that 11 patients had no impairment of glomerular filtration after administration of captopril. MR imaging showed that four had impairment of glomerular filtration: studies without captopril were symmetric (n = 2) or slightly asymmetric (n = 2), but administration of captopril induced severe functional impairment on the side of stenosis--that is, a delayed tubular phase with late corticomedullary decrease of signal intensity in the first two patients and absence of tubular phase in the other two. The results of scintigraphy were concordant in all but one case, in which the segmental distribution of filtration impairment, shown by MR imaging, was not shown by scintigraphy. The renal artery stenosis was shown by MR angiography in 10 of 15 patients (67%). CONCLUSION: Captopril-sensitized dynamic MR imaging of the kidney is feasible in patients with renovascular hypertension. However, captopril-induced changes are not present in all patients proven to have the disease. Scintigraphy provides similar results but may ignore segmental functional involvement.

Angiotensin-Converting Enzyme Inhibitors↗
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↗
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↗
PubMed1993

Pontine myelinolysis following liver transplantation: a report of two cases.

Two cases of central pontine myelinolysis (CPM) following orthotopic liver transplantation (OLT) are reported. Several months after the onset of this neurological syndrome, the two patients are still alive but with severe neurological sequelae. Some patients undergoing emergency OLT present a high risk of CPM because of pre-existing malnutrition, encephalopathy, and hepatic insufficiency. All of these are associated with an inevitable abrupt rise in sodium serum concentration due to intraoperative compensation of blood losses with high-sodium content blood products. Whenever the renal capacity to excrete sodium is impaired by the surgical procedure, continuous intraoperative venovenous hemofiltration is recommended.

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↗
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↗
PubMedDate not supplied

External iliac vein stenosis after segmental pancreatic transplantation: treatment by percutaneous endoprosthesis.

A stenosis of the iliac vein secondary to a fluid collection in a pancreas transplant was identified by color Doppler flow sonography. The pancreatic venous drainage was reversed to the contralateral iliac veins via venous collaterals. After two unsuccessful angioplasties of the vein stenosis, a Wallstent was positioned above the venous anastomosis, and has remained patent for 8 months. The pancreatic venous drainage became normal after the procedure.

Constriction, Pathologic↗
PubMedDate not supplied

MR imaging of foraminal and extraforaminal lumbar disk herniations.

Foraminal and extraforaminal disk herniations are less frequent than intraspinal herniations at the lumbar level and more difficult to diagnose. They are undetected by myelography and distinction between them and an enlarged nerve root may be difficult with CT. Thirty-three patients presenting with persistent radiculopathy and showing an image suggesting a far lateral disk herniation on CT at 34 disk levels were prospectively imaged with magnetic resonance (MR). In all cases the disk fragment was identified and its separation from the nerve root was possible. This separation was more readily visible on sagittal or angled coronal views. The exact location of the herniation in relation to the facet joints and the pedicles was best assessed with MR: Ten were purely intraforaminal, 8 extraforaminal, and 15 both. Cephalad migration was noted on the sagittal lateral facet plane in 71% of cases. Surgical correlations were available for 25 disks. Three were falsely positive for disk herniation. Enlarged foraminal veins were responsible for this appearance as confirmed by surgery in two of these. When a prediction of disruption of the lateral extension of the posterior longitudinal ligament was made, it was confirmed at surgery in 52% of cases because of extreme lateralization of the herniations.

Adult↗
PubMedDate not supplied

[Conservative treatment of hepatic injuries. Management and course].

From January 1986 to June 1994, 252 cases of closed liver trauma were treated in an emergency setting. Non surgical conservative management, after a complete imaging work-up including CT scan in all cases, was applied in 142 cases (56.3%) with no hemodynamic complication. The spontaneous outcome in these cases was quite favourable in 131 (92.2%); all lesions had disappeared in 4 to 36 weeks. Complications were observed in only 6 cases: 2 intrahepatic abscesses managed with percutaneous drainage were not further complicated, 1 biliari fistula required surgical exploration, 1 intrahepatic bilioma was drained percutaneously, 1 disinsertion of the gallbladder was treated by laparoscopy and 1 operation for bleeding was required 48 hours after the trauma in 1 case. No deaths could be directly imputed to the liver trauma, 5 patients died from neurological causes. Non-surgical conservative treatment combined with strict prolonged surveillance is a reliable management option for patients with closed liver trauma.

Adolescent↗