Biomedical subjects

Tim Leiner

Publications and source records attributed to Tim Leiner.

24 records · Page 2Linked to original sources

PubMed2003

Stenosis detection in forearm hemodialysis arteriovenous fistulae by multiphase contrast-enhanced magnetic resonance angiography: preliminary experience.

PURPOSE: To assess the feasibility and accuracy of multiphase contrast-enhanced magnetic resonance angiography (CE-MRA) in patients with dysfunctioning hemodialysis arteriovenous fistulae (AVF), using digital subtraction angiography (DSA) as the standard of reference. MATERIALS AND METHODS: Fifteen patients with dysfunctioning AVF (eight radiocephalic and seven graft AVF) underwent CE-MRA. Dysfunction was defined as a flow decline of more than 25% in 1 month measured by dilutional flow measurements. CE-MRA was performed during injection of 35 mL of gadolinium-DTPA. The CE-MRA sequence consisted of a time-resolved series of 10 scans, each lasting approximately 10 seconds. The technical parameters were TR/TE/FA/voxel = 5.4/1.6/40/3.1 mm(3), and a rectangular surface reception coil was used. All patients were scheduled to undergo DSA at which an intervention was carried out when a stenosis >or=50% was seen. Two observers, unaware of each other's findings and the findings at DSA, quantified the number and degree of stenosis in the failing AVF. Image quality for CE-MRA and DSA was scored on a 3-point scale. The diagnostic performance of CE-MRA was analyzed with receiver-operator characteristic (ROC) analysis. RESULTS: CE-MRA and DSA examinations were performed without side effects in all 15 patients. Image quality was scored significantly better on CE-MRA (observer 1: CE-MRA, 2.0; DSA, 1.3; P =.001; observer 2: CE-MRA, 2.0; DSA, 1.4; P =.002). Interobserver agreement for detection of >or=50% stenosis was 0.81 (95% confidence interval (CI) = 0.71-0.92) for CE-MRA and 0.69 (95% CI = 0.55-0.84) for DSA. ROC analysis revealed a mean area under the curve of 0.78. On the patient level, at the >or=50% threshold, mean sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 100% (95% CI = 69%-100%), 10% (95% CI = 0%-78%), 70% (95% CI = 38%-92%), and 100% (95% CI = 50%-100%), respectively. At the >or=75% threshold, mean sensitivity, specificity, PPV, and NPV were 75% (95% CI = 20%-99%), 78% (95% CI = 39%-98%), 55% (95% CI = 12%-96%), and 89% (95% CI = 52%-100%), respectively. CONCLUSION: CE-MRA is a useful diagnostic tool for detecting stenoses in flow-declined hemodialysis AVF prior to interventional DSA.

Aged↗

PubMed2003

Contrast-enhanced peripheral MR angiography at 3.0 Tesla: initial experience with a whole-body scanner in healthy volunteers.

PURPOSE: To report preliminary experience with contrast-enhanced magnetic resonance angiography (CE-MRA) of the peripheral arteries on a 3.0 T whole-body scanner equipped with a prototype body coil. MATERIALS AND METHODS: Four healthy volunteers were imaged on the 3.0 T system and, for comparative purposes, two of the subjects were also imaged on a commercially available 1.5 T whole-body system. To investigate field strength influence on objective image quality, signal-to-noise (SN) and contrast-to-noise (CN) ratios were calculated for named vessels from the infrarenal aorta to the ankles at both field strengths. Comparable imaging protocols were used at both field strengths. In addition, two reviewers, blinded for field strength, gave subjective image quality scores (three-point scale). RESULTS: SN and CN ratios were approximately equal on both systems (variation < or =9%) for the iliac and proximal upper leg stations. For the popliteal and lower leg stations SN ratios were 36% and 97% higher, and CN ratios were 44% and 127% higher, at 3.0 T. Subjective image quality at 3.0 T was substantially better for the distal upper and lower legs. CONCLUSION: Contrast-enhanced peripheral MRA is possible at 3.0 T when an imaging protocol similar to a current state-of-the-art 1.5 T protocol is used. Objective and subjective image quality at 3.0 T is comparable for the iliac and upper legs but better for the popliteal and lower leg arteries.

Adult↗

PubMed2003

Comparison of treatment plans for peripheral arterial disease made with multi-station contrast medium-enhanced magnetic resonance angiography and duplex ultrasound scanning.

OBJECTIVE: This study was undertaken to investigate the effects of substituting multi-station total outflow contrast medium-enhanced magnetic resonance angiography (CE-MRA) for color duplex ultrasound (US) scanning on treatment planning in the diagnostic workup of patients with suspected or known peripheral arterial occlusive disease. Patients and methods One hundred consecutive patients referred because of suspected or proved peripheral arterial occlusive disease to a University Hospital underwent both aortoiliac duplex US scanning and multi-station total outflow CE-MRA. For 73 of these patients (57% men; mean age, 62 years) treatment or treatment plans could be retraced. Eighteen patients also underwent femoro-popliteal duplex US scanning. Three experienced vascular surgeons retrospectively formulated two sets of treatment plans based on standardized clinical parameters and either duplex US scanning or CE-MRA. The main outcome measure was proportion of patients for whom the treatment plan matched actual treatment without additional use of intra-arterial digital subtraction angiography. Actual treatment, based on all available information, including results of duplex US scanning, CE-MRA, and any other diagnostic tests, served as the standard of reference. RESULTS: Duplex US scanning provided enough information for treatment planning in 46, 45, and 53 patients versus 67, 68, and 66 patients when CE-MRA was used (surgeons 1, 2, and 3, respectively; surgeons 1 and 2, P <.001; surgeon 3, P =.007). Treatment plans based on duplex US scanning exactly matched actual treatment in 37 of 73 patients (51%; surgeon 1), 36 of 73 patients (49%; surgeon 2), and 46 of 73 patients (63%; surgeon 3). Treatment plans based on CE-MRA exactly matched actual treatment in 56 of 73 patients (77%; surgeon 1), 55 of 73 patients (75%; surgeon 2), and 51 of 73 patients (70%; surgeon 3). Positive predictive value and negative predictive value of duplex US scanning as measures of ability to discriminate between surgical and nonsurgical treatment were 0 of 0 (undefined) and 43 of 46 (93%), 1 of 2 (50%) and 40 of 43 (93%), and 5 of 5 (100%) and 44 of 48 (92%) for surgeons 1, 2, and 3, respectively. For CE-MRA, positive and negative predictive values were 11 of 13 (85%) and 50 of 54 (93%), 10 of 12 (83%) and 51 of 56 (91%), and 8 of 13 (62%) and 48 of 53 (91%), respectively, for surgeons 1, 2, and 3. CONCLUSION: Compared with aorto-iliac and femoro-popliteal duplex US scanning, multi-station total outflow CE-MRA is more effective for treatment planning in most patients with known or suspected peripheral arterial occlusive disease.

Adult↗

PubMed2002

Safety of contrast-enhanced MR angiography employing gadobutrol 1.0 M as contrast material.

Our objectives were to evaluate the safety of intravenous 1.0-M gadobutrol injections in patients with an indication for contrast-enhanced magnetic resonance angiography (CE MRA) of supra-aortal, pelvic, or peripheral arteries by examining and assessing adverse events, laboratory values, vital signs and ECG findings for clinical significance. In 435 patients, recruited in three multicenter trials for safety evaluations of the new contrast agent 1.0-M gadobutrol, CE MRA was performed with 1.0- to 1.5-T scanners using three-dimensional gradient-echo sequences and phased-array coils. The study population comprised 312 men and 123 women with a mean age of 60.9 years. Two hundred seven patients had an indication for imaging of body arteries and 228 had an indication for imaging of peripheral arteries. Blood laboratory values and urinalysis results of 124 patients as well as heart rate, blood pressure, and 12-lead-electrocardiogram readings of 93 patients obtained during a follow-up period of up to 72 h after the injection of contrast media were available for safety analysis. Contrast media application was performed as intravenous bolus injection of 1.0-M gadobutrol in fixed doses according to the patients' body weight (b.w.) and indication for CE MRA and was followed by a 20- to 40-ml saline flush. Mean dose actually applied was 0.1 0.27 mmol/kg b.w. Flow rate ranged between 0.2 and 2.0 ml/s. Safety evaluations found a good tolerability with only 4.6% of at least "possibly related" adverse reactions and no clinically relevant changes in blood and urine samples including no transmetallation effect on serum zinc values. Analysis of renal tolerance showed no influence on renal function irrespective of preexisting renal impairment. The ECG analysis (rhythm analysis, pace-setting disturbances, conduction disturbances, and time interval measurements, including uncorrected and corrected QT) showed no clinically relevant effect of the injection of 1.0-M gadobutrol on the cardiac conduction system. Intravenous injection of 1.0-M gadobutrol at a dose of up to 0.1 0.27 mmol/kg b.w. in the indication CE MRA is safe and causes no clinically relevant changes in safety parameters such as heart rate, blood pressure, blood and urine laboratory values, and cardiac conduction system.

Adult↗

PubMed2002

Motion of the distal renal artery during three-dimensional contrast-enhanced breath-hold MRA.

PURPOSE: To study the potential detrimental effects of renal motion on breath-hold three-dimensional contrast-enhanced (CE) magnetic resonance angiography (MRA). MATERIALS AND METHODS: A computer model simulating linear motion was applied to MRA pulse sequences. Subsequently, to study whether renal motion was present, 24 patients being evaluated for possible renovascular hypertension underwent a breath-hold nonenhanced single slice two-dimensional dynamic turbo field-echo magnetic resonance imaging (MRI) scan with a typical duration of 32 seconds. This sequence was followed by breath-hold three-dimensional CE renal MRA. CE-MRA images were evaluated by two independent observers. RESULTS: The computer model revealed linear renal motion to cause artifacts. The severity of these artifacts correlated with velocity. Significant (P < 0.001) near linear cranial motion of the kidneys and diaphragm during a sustained breath-hold was found for the right kidney, left kidney, right diaphragm, and left diaphragm (0.26 +/- 0.21 mm/second, 0.25 +/- 0.23 mm/second, 0.43 +/- 0.43 mm/second, and 0.29 +/- 0.33 mm/second [mean +/- SD], respectively). CE-MRA images showed artifacts of the distal renal artery that corroborated the computer model findings. CONCLUSION: The observed cranial motion of the kidneys during a breath-hold adversely affects distal renal artery image quality on three-dimensional CE-MRA and jeopardizes reliable clinical evaluation. Shortening scan time may be beneficial for decreasing image degradation caused by this phenomenon.

Adult↗

PubMed2002

Medical imaging techniques in the evaluation of strategies for therapeutic angiogenesis.

Recent advancements in our understanding of the basic biology of angiogenesis have prompted a focus on practical applications, both in cardiovascular disease and in oncology. The focus on practical applications has stimulated development of novel noninvasive tools that provide serial assessment of ongoing vessel growth in vivo. Nuclear imaging (SPECT, PET) and x-ray angiography have been used to assess changes in perfusion and anatomic appearance, respectively, after induced neovascular development. New MRI techniques provide the ability to identify early changes in vivo that are more sensitive to detection of the effects of new vessel growth than x-ray angiography or nuclear imaging. These new MRI techniques include measurement of blood delivery to the myocardium, development of intramyocardial vasculature, and incremental changes in regional myocardial contractile function. With the combination of methods now available, we expect to be able to track key steps of angiogenesis in vivo and to assess the efficacy of angiogenic therapies. These new imaging capabilities offer crucial information which we hope will hasten the identification and deployment of effective pharmaceutical therapies as an adjunct or alternative to invasive treatments of ischemic disease by targeted stimulation of angiogenesis, and of cancer, by targeted inhibition of angiogenesis.

Animals↗