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M R Engelbrecht

Publications and source records attributed to M R Engelbrecht.

8 recordsLinked to original sources
PubMed2001

Accurate estimation of pharmacokinetic contrast-enhanced dynamic MRI parameters of the prostate.

Quantitative analysis of contrast-enhanced dynamic MR images has potential for diagnosing prostate cancer. Contemporary fast acquisition techniques can give sufficiently high temporal resolution to sample the fast dynamics observed in the prostate. Data reduction for parametric visualization requires automatic curve fitting to a pharmacokinetic model, which to date has been performed using least-squares error minimization methods. We observed that these methods often produce unexpectedly noisy estimates, especially for the typically fast, intermediate parameters time-to-peak and start-of-enhancement, resulting in inaccurate pharmacokinetic parameter estimates. We developed a new curve fit method that focuses on the most probable slope. A set of 10 patients annotated using histopathology was used to compare the conventional and new methods. The results show that our new method is significantly more accurate, especially in the relatively less-enhancing peripheral zone. We conclude that estimation accuracy depends on the curve fit method, which is especially important when evaluating the peripheral zone of the prostate.

Aged↗
PubMed2001

Bismuth overdosing-induced reversible nephropathy in rats.

Overdosing of colloidal bismuth subcitrate (CBS), used to treat peptic ulcers and Helicobacter pylori infections, has been reported to result in serious, though reversible, nephrotoxicity in humans. However, little is known about the nature of the renal damage induced by bismuth (Bi), and no well-described experimental model exists. Single large oral CBS doses (0.75, 1.5, and 3.0 mmol Bi/kg) were administered to three groups of 20 female Wistar rats. A control group (n = 20) received only the vehicle. Standard kidney function parameters, urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) and the Bi content were monitored in blood, urine, liver, and kidneys for 14 days. A dose of 3.0 mmol Bi/kg, 100 times the daily therapeutic dose, caused kidney damage within 6 h as detected by proteinuria, glucosuria, and elevated plasma urea and plasma creatinine levels. The kidneys of all animals, except two that died, recovered functionally within 10 days. At a dose of 1.5 mmol Bi/kg, clinical parameters changed less and normalized within 48 h, whereas a dose of 0.75 mmol Bi/kg induced no changes. Histological evaluation revealed that the S3 tubular segment necrotized first with additional necrotization of the S1/S2 segment when more Bi was absorbed. The lesions were accompanied by interstitial infiltrates of CD45+ leukocytes. In summary, we developed a rat model for Bi-induced reversible nephropathy. A large single oral overdose of CBS administered to Wistar rats led to damage to the proximal tubule, especially in the last segment.

Acetylglucosaminidase↗
PubMed2001

Patient selection for magnetic resonance imaging of prostate cancer.

BACKGROUND: Routine magnetic resonance (MR) imaging for local staging of prostate cancer is controversial, due to moderate staging performance. However, MR imaging may be beneficial in a subgroup of patients with clinically localized prostate cancer. OBJECTIVE: To define the patient group in which local staging of prostate cancer using MR imaging is useful for treatment outcome. METHODS: We used a decision analytic model based on data found in the literature to define the patient subgroup which may benefit from local staging with MR imaging. We applied the threshold approach to calculate the threshold where direct surgery and surgery after MR imaging (surgery-MR imaging threshold) result in equal utility. Additionally, we calculated the threshold where direct radiation and radiation after MR imaging (MR imaging-radiotherapy threshold) result in equal utility. RESULTS: We found that the surgery-MR imaging threshold was at a probability of 45% of having stage > or =T(3) disease. The MR imaging-radiotherapy threshold was at a prior probability of 81% of having stage > or =T(3) disease. CONCLUSIONS: The application of the threshold approach indicated that MR imaging should be limited to patients with an intermediate-high risk of having stage T(3) disease.

Aged↗
PubMed1999

MR imaging of the male pelvis.

Prostate and urinary bladder cancer are the most frequently encountered malignancies of the urinary tract. Appropriate use of the different imaging techniques is crucial for accurate assessment of prognosis and for the development of appropriate treatment planning. Especially determination of local tumor extension and detection of nodal or bone metastases is extremely important. In this regard MR imaging is the most promising imaging technique. Therefore, in this review its role in staging these malignancies is evaluated and compared with clinical staging, and other imaging techniques. Finally, future developments, such as new sequences, new contrast agents, the role of surface coils and MR-guided biopsy, are considered. Also, the preferred radiological approach is discussed.

Humans↗
PubMed1999

Quantitative analysis of ultrasonic B-mode images.

Various sources of variability, such as speckle noise, depth dependence and inhomogeneous intervening tissue, are involved in B-mode images, even when using the same ultrasonic equipment with fixed settings. The behavior of these sources of variability was investigated by texture analysis of images obtained from simulations and from a tissue-mimicking phantom, a normal adult liver and a pediatric renal (Wilms') tumor. First-order statistics (MEAN and SNR) and second-order statistics from the co-occurrence matrix (ENT and COR) were calculated. In a phantom, the SNR and ENT show a clear depth dependence. In biological tissue, the variability is mainly caused by the speckle noise and inhomogeneous intervening tissue. In addition, almost the entire range of the COR feature is present in images of liver and tumor. Furthermore, all the features calculated in windows of 1 cm2 exhibit an overlap among the different media. With the second-order features, it is possible to discriminate 85% reliable (average) between the normal, adult, liver and the pediatric renal tumor above a window size of 9 cm2. The SNR can not discriminate between these tissues. The maximum resolution of 9 cm2 reveals a serious limitation of parametric imaging. Finally, the features reproduce well in the case of follow-up of an abdominal tumor during chemotherapy.

Adult↗
PubMed1998

Follow-up of Wilms' tumour during pre-operative chemotherapy by qualitative and quantitative sonography.

OBJECTIVES: Evaluation of textural changes in Wilms' tumour during chemotherapy by qualitative and quantitative ultrasonography. METHODS: Sonograms of Wilms' tumours during chemotherapy were retrospectively evaluated (N=33) and compared with histopathology. Textural changes were prospectively quantified (N=6) by mean echogenicity (MEAN) and coefficient of variation (CV) of grey levels. RESULTS: Interobserver agreement for volume measurements was strong and for follow-up of sonolucencies moderate. Chemotherapy caused significant volume reduction and two major patterns of change in sonolucencies were observed; either increase or no change. No relationship between sonolucencies and volume changes was present. Sonolucencies yielded an underestimation of necrosis (P<0.001). Trends in MEAN and CV differed between patients. CONCLUSIONS: Volume was the most objective sonographic tumour response parameter. Changes in sonolucencies may provide additional information on tumour response. However, sonolucencies are not an accurate measure of total tumour necrosis. It was not possible to differentiate Wilms' tumour chemotherapy responders from non-responders by MEAN and CV.

Adolescent↗
PubMedDate not supplied

Contrast-enhanced 3D-TOF MRA of peripheral vessels: intravascular versus extracellular MR contrast media.

MR contrast media have been used to improve MR angiography (MRA). Their effect has been particularly beneficial for extracranial MRA. This study evaluated the efficacy of a new formulation of ultrasmall superparamagnetic iron oxide particles (USPIO) on three-dimensional (3D) time of flight (TOF) MRA in the pelvis and lower limb circulation. Each of six dogs received 3 mg/kg of USPIO and .2 mmol/kg of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) bis-methylamide (BMA) by intravenous infusion on separate examinations. Precontrast and postcontrast 3D-TOF MRA images of the lower extremities were acquired over the course of 45 minutes postinjection. Signal intensity (SI) was measured on axial views along the external iliac, femoral, and popliteal arteries. USPIO provided clear demarcation of the major primary, secondary, and tertiary vessels and the improved contrast-to-noise ratio (CNR) was maintained for 45 minutes. Gd-DTPA-BMA provided less signal enhancement than USPIO. The increase in CNR with this agent had significantly declined by 15 minutes after injection. The major vessels could no longer be visualized at 30 and 45 minutes after injection of Gd-DTPA-BMA This study demonstrates the efficacy of USPIO as a contrast medium for 3D-TOF MRA. It was concluded that USPIO provided effective and persistent enhancement of the peripheral vessels.

Animals↗