Biomedical subjects

J T Heverhagen

Publications and source records attributed to J T Heverhagen.

At least 19 recordsLinked to original sources

PubMed2004

Benign prostate hyperplasia: evaluation of treatment response with DCE MRI.

Benign prostate hyperplasia (BPH) is a major disease and its non-surgical therapy a major area of interest. The purpose of this study was to establish perfusion parameters in beagles with BPH using dynamic contrast-enhanced (DCE) MRI and to investigate changes due to the effects of finasteride treatment. Twelve male beagles (mean age 4.4 +/- 0.9,years) were divided into a control and treatment group that received a daily dose of 1 mg/kg finasteride. DCE MRI was carried out in a clinical scanner using a 3D spoiled gradient echo sequence prior to and during treatment. 0.2 mmol/kg contrast agent (gadoteridol) was administered with an injection rate of 0.2 ml/s followed by a 15 ml flush of saline. Contrast enhancement was evaluated by pharmacokinetic mapping of a two-compartment model with colour overlay images in addition to regional ROI analysis. Quantitative parameters were defined by the amplitude of contrast enhancement A, the exchange rate k(ep) and the time to maximum signal enhancement. Dynamic contrast-enhanced MRI investigations of the prostate revealed two distinct zones, an inner, periurethral zone and an outer, parenchymal zone. The periurethral zone is highly vascularized, whereas the parenchymal zone is moderately vascularized when compared to other parenchymal organs. During treatment, in the parenchymal zone the intensity of enhancement (amplitude A) and the time to maximum signal enhancement increased, while the exchange rate k(ep) decreased. Dynamic contrast-enhanced MRI of BPH reveals distinct differences between individual zones within the prostate. Moreover, changes during successful treatment suggest increased blood volume per volume of tissue and decreased vessel leakiness.

Animals↗

PubMed2004

[Clinical high- and ultrahigh-field MR and its interaction with biological systems].

The field strength of the static field in MRI has increased from 0.015 to 12 Tesla (T) during the last 25 years, which is about an 800 fold increase. In addition to low- and high field systems (1.5-4 T), ultra-high field systems with field strengths above 4 T are now available for human MRI. The extension of non-significant risk status for clinical fields up to 8 T by the FDA in July 2003 facilitates the further growth of this technology. The increase in field strength creates the need for a better understanding of the safety challenges to ensure safety for human imaging applications. This encompasses understanding the effects of the strong magnetic field at the atomic and molecular level and from biological tissue to organ systems. Moreover, in addition to the effects of a static magnetic field, the effects of radio-frequency- and gradient-fields have to be considered. This paper reviews the safety relevant issues for high- and ultrahigh field MR.

Equipment Safety↗

PubMed2004

[Clinical MR at 3 Tesla: current status].

Clinical MRI is mostly performed at field strengths up to 1.5 Tesla (T). Recently, approved clinical whole-body MR-systems with a field strength of 3 T became available. Its installation base is more rapidly growing than anticipated. While site requirements and operation of these systems do not differ substantially from systems with lower field strength, there are differences in practical applications. Imaging applications can use the gain in signal-to-noise for increased spatial resolution or gain in speed. This comes at a trade off in increased sensitivity to field inhomogeneities and changes in relaxation times, which lead to changes in image contrast. The benefit of high field for spectroscopy consists in increased signal-to-noise-ratio and improvement in frequency resolution. The increase in energy deposition necessitates the use of special strategies to reduce the specific absorption rate (SAR). This paper summarizes the current state of MR at 3 T.

Artifacts↗

PubMed2004

Primary and transplanted ENU induced rat tumors in neurooncology.

In neurooncology transplanting, tumors can be used for many purposes e.g. to solve questions concerning the etiology and pathogenesis of such tumors or their management. Experimentally induced and transplanted tumors of the nervous system become reproducible in their morphology and growth parameters after about 12 subsequent intracerebral passages. During the period from the first to the 12th intracerebral generations, a simplification of the histology and a reduction of the induction times take place. Nowadays the growth behavior of such tumors can be followed by imaging methods such as MRI if specially adapted to small animals. Our results are based on the investigation of over 2350 experimentally induced tumors of the central and peripheral nervous system that were diagnosed according to the rules of human and rodent brain tumor classification and various subgroups of this sample, analyzed by electron microscopy, postmortal angiography and MRI.

Animals↗

PubMed2004

Analysis of mice tumor models using dynamic MRI data and a dedicated software platform*.

PURPOSE: To implement a software platform (DynaVision) dedicated to analyze data from functional imaging of tumors with different mathematical approaches, and to test the software platform in pancreatic carcinoma xenografts in mice with severe combined immunodeficiency disease (SCID). MATERIALS AND METHODS: A software program was developed for extraction and visualization of tissue perfusion parameters from dynamic contrast-enhanced images. This includes regional parameter calculation from enhancement curves, parametric images (e. g., blood flow), animation, 3D visualization, two-compartment modeling, a mode for comparing different datasets (e. g., therapy monitoring), and motion correction. We analyzed xenograft tumors from two pancreatic carcinoma cell lines (BxPC3 and ASPC1) implanted in 14 SCID mice after injection of Gd-DTPA into the tail vein. These data were correlated with histopathological findings. RESULTS: Image analysis was completed in approximately 15 minutes per data set. The possibility of drawing and editing ROIs within the whole data set makes it easy to obtain quantitative data from the intensity-time curves. In one animal, motion artifacts reduced the image quality to a greater extent but data analysis was still possible after motion correction. Dynamic MRI of mice tumor models revealed a highly heterogeneous distribution of the contrast-enhancement curves and derived parameters, which correlated with differences in histopathology. ASPC1 tumors showed a more hypervascular type of curves with faster and higher signal enhancement rate (wash-in) and a faster signal decrease (wash-out). BXPC3 tumors showed a more hypovascular type with slower wash-in and wash-out. This correlated with the biological properties of the tumors. CONCLUSION: With the described software, it was possible to analyze tissue perfusion parameters in small xenograft tumor models in mice. Our data correlated with histopathological data, and the qualitative and quantitative perfusion parameters could distinguish two tumor entities with different growth characteristics.

Animals↗

PubMed2002

Does the application of gadolinium-DTPA have an impact on magnetic resonance phase contrast velocity measurements? Results from an in vitro study.

INTRODUCTION/OBJECTIVE: To evaluate the potential influence of various concentrations of gadolinium (Gd)-DTPA on magnetic resonance phase contrast (MR PC) velocimetry. MATERIAL AND METHODS: Imaging was done with a 1.0 T scanner using a standard Flash 2D sequence and a circular polarized extremity coil. In a validated flow phantom with a defined 75% area stenosis different concentrations of Gd-DTPA, diluted in a 10:1 water-yogurt mixture, MR PC measurements were correlated with a Doppler guide wire as gold standard. RESULTS: MR PC measurements correlated well with the Doppler derived data (r=0.99; P<0.01; maximum pre-stenotic velocity: 21.6+/-0.5 cm/s; maximum intra-stenotic velocity: 81.7+/-0.6 cm/s). Following Gd-DTPA administration no significant (P>0.05; Student's t-test) flow measurement changes were noted (maximum pre-stenotic velocity: 21.3+/-1.3 cm/s; maximum intra-stenotic velocity: 84.0+/-3.6 cm/s). However, delineation of the perfused lumen was enhanced after the application of Gd-DTPA. DISCUSSIONS AND CONCLUSION: The application of Gd-DTPA does not affect MR PC velocimetry. However, the application of contrast media allowed a more accurate vessel segmentation. MR PC measurements can be reliably carried out after application of Gd-DTPA.

Blood Flow Velocity↗

PubMed2002

Magnetic resonance phase contrast velocity measurement for non-invasive follow up after percutaneous transluminal angioplasty.

BACKGROUND: The aim of this study was to evaluate magnetic resonance phase contrast velocimetry (MRVL) as a non-invasive follow up tool to assess restenosis after percutaneous transluminal angioplasty (PTA). PATIENTS AND METHODS: We prospectively investigated 51 consecutive patients who underwent PTA of the femoropopliteal region. MRVL was conducted prior, one day, six weeks, twelve weeks and 24 weeks after PTA using a circular polarized extremity coil and a gradient echo sequence (TR/TE 600/6 ms, flip angel 30 degrees, slice thickness 10 mm). Hemodynamic data, derived from the MR phase contrast sequence, allowed to calculate the degree of area stenosis of the lesion treated with PTA. These data were correlated with clinical hemodynamic parameters (ankle-brachial index and walking distance). RESULTS: The mean grade of area stenosis was 69% +/- 27% before PTA, 30% +/- 20% one day, 29% +/- 23% six weeks, 39% +/- 17% twelve weeks and 42% +/- 18% 24 weeks after PTA and correlated well with clinical data and the post angioplasty clinical course of the patients. CONCLUSIONS: Follow up measurements using MRVL are suitable to assess restenosis after PTA and allow quantifying the grade of recurrent stenosis as well as the hemodynamic consequences.

Aged↗

PubMed2002

Magnetic resonance hydrometry: non-invasive quantification of the exocrine pancreatic function.

AIMS: To show the ability of magnetic resonance hydrometry (MRH) to quantify the pancreatic secretion after secretin stimulation in order to distinguish between physiological excretion and reduced output in chronic pancreatitis. METHODS: MRH images were acquired in a 1.0-T-clinical scanner using a body-array coil and a heavily T2-weighted standard single-shot TSE sequence. Thirty-one patients (14 male/17 female) who routinely underwent ERCP for suspected choledocholithiasis (n = 22), recurring abdominal pain (n = 1), icterus (n = 6 and suspected pancreatitis (n = 2) were included. During the investigation 1 CU/kg BW secretin were administered intravenously. Secreted volume of fluid, start of secretion, achievement of a plateau of secretion and a combined score of these parameters (MRH score) were assessed and evaluated. Sensitivity and specificity were calculated for these parameters. RESULTS: 27 patients had no pancreatic pathology, and four suffered from chronic pancreatitis. Patients without pancreatic disorders produced a mean pancreatic fluid volume of 183 plus minus 86 mL, whereas patients with chronic pancreatitis secreted 61 +/- 39 mL. Secretion started after a mean time of 95 +/- 94 seconds (no pancreatic impairment) and 62 +/- 13 seconds (chronic pancreatitis). The MRH score achieved a high accuracy in the detection of chronic pancreatitis. CONCLUSIONS: Our study demonstrated the feasibility of measuring pancreatic output by MRH after stimulation with secretin. Moreover, a distinction between normal secretion and patients with chronic pancreatitis is possible.

Adult↗

PubMed2002

[Secretin-stimulated MR cholangiopancreatography (MRCP): visualization of the normal pancreatic duct in comparison with ERCP].

PURPOSE: To determine whether the application of secretin improves the depiction of the normal pancreatic duct and to document the time course of any possible improved visualisation. PATIENTS AND METHODS: Twenty-eight patients with a normal pancreatic ductal system, proved by ERCP, were prospectively enrolled in our study. MRCP was carried out in a 1.0 Tesla unit using a thick slab single-shot turbo-echo sequence (TR: infinity, TE: 1100 ms, FA: 150 degrees, slab thickness: 65 mm). Following acquisition of a non-enhanced image, 1 clinical unit/kg bodyweight of secretin was injected intravenously. During the subsequent ten minutes the MR measurement was repeated every 30 seconds. The images were independently evaluated by two investigators. RESULTS: The improvement in quality after administration of secretin was statistically significant for both investigators (p < 0.05), but no significant difference was found between both investigators concerning the quality of the images (p = 0.49). Prior to the secretin application, the entire ductal system only be evaluated in ten cases (35.7 %) by both investigators, afterwards in 26 cases (92.9 %). Improvement was achieved after a mean time of 1.5 minutes and lasted until the ninth minute. CONCLUSION: Intravenous application of secretin improves image quality of MRCP also in patients with no pancreatic pathology. Improvement begins after 1.5 minutes and lasts for about seven minutes.

Adult↗

PubMed2002

Rotational digital cholangiography (RDC) and 3D-cholangiography (3DC) for guidance of percutaneous biliary drainage procedures.

PURPOSE: To evaluate whether RDC and 3DC help clarifying anatomic details in biliary duct disease and is useful for guidance of drainage procedures. MATERIALS AND METHODS: RDC was conducted in 11 consecutive patients (8 male, 3 female, mean age 63 years). Nine patients underwent PTBD for malignant biliary duct stenosis, one patient because of ischemic stenosis after hepaticojejunostomy and one patient presented with an infected biloma. Images were obtained after initial bile duct puncture during single breath hold from 120 projection angles using a rotating C-arm. These images were immediately available and evaluated in order to facilitate the definitive drainage procedure. For additional 3D reconstruction, data were sent to a dedicated workstation and judged by a blinded observer. RESULTS: The availability of a rotating data set of images was judged to be helpful in three patients with complex anatomical situations. Additionally, RDC holds the potential to reduce fluoroscopy time. 3DC allowed analysis of the hepatic bifurcation from different viewing angles in 10 cases with high spatial resolution (mean voxel size 480 micro micro m 3). This may allow a better classification of hilar obstructions according to our preliminary observations. CONCLUSION: Images from RDC and 3DC are helpful in guiding PTBD procedures and for better diagnosis in selected patients with hilar biliary duct stenoses.

Adult↗

PubMed2001

Feasibility of MRI in the diagnosis of acute diverticulitis: initial results.

PURPOSE: The purpose of this study was to evaluate MRI as a diagnostic tool in patients with suspected acute sigmoid diverticulitis. Furthermore, we sought to develop an optimal imaging protocol in these patients. PATIENTS AND METHODS: Eleven patients with suspected acute diverticulitis were included in the study. All patients were imaged in a 1.0 T clinical scanner using a body-array coil. Imaging sequences were single-shot TSE, HASTE-, STIR- and TrueFisp- sequence. All were obtained in the frontal plane. The diagnosis was verified by a single experienced investigator, using ultrasound, and overall clinicopathological outcome. RESULTS: MRI enabled visualization of signs of an acute diverticulitis in all patients. However, the diagnosis of acute diverticulitis was obtained in 10 patients only. The mean imaging time was 17.5+/-5.5 min. STIR- and TrueFisp-sequences alone displayed all findings, e.g pericolonic exsudation, edema and segmental narrowing, whereas SSTSE and HASTE-sequences showed no additional information. Therefore, it appeared that the imaging protocol could be restricted to STIR- and TrueFisp-sequences. CONCLUSION: MRI is feasible as a fast, accurate and investigator-independent diagnostic tool in patients with suspected acute diverticulitis. To prove its value in comparison to computed tomography or ultrasound, further studies are needed.

Acute Disease↗

PubMed2001

Kinetic evaluation of an i.v. bolus of MR contrast media.

Currently, it is assumed that the pharmacokinetic properties of the first minutes of an I.V. MR contrast media bolus are similar to those of an i.v. iodinated contrast media bolus used in CT. Correct timing of an MRA examination is crucial for obtaining sufficient arterial contrast. This study sought to evaluate the temporal change of arterial signal intensity within 150 s after i.v. bolus injection of Gd-DTPA. Thirty consecutive patients (14 women/16 men; mean age: 51 +/- 11 years) were prospectively examined with a 1.0 Tesla clinical scanner. A single axial slice was acquired in 1.25 sec with manufacturer provided gradient echo sequence through the aorta at the level of the renal arteries. Investigation was started simultaneously to the application of contrast media (0.1 mmol/kg bodyweight Gd-DTPA at three different rates 2 mL/sec, 3 mL/sec and 4 mL/sec) and repeated for 2.5 min. An additional echo Doppler examination excluded patients with any cardiac disorders. Maximum signal (1300% increase compared to the basic value) in the aorta was achieved 20 +/- 6 sec after start of bolus injection. Then a plateau phase was maintained for the remaining investigation time (2.5 min). No significant difference was shown for different injection rates. After a bolus injection of Gd-DTPA the arterial contrast remains on a high level for at least 2 min. However, correct timing of the bolus arrival is still crucial to discriminate arteries and veins. An injection rate between 2 mL/sec and 4 mL/sec has no influence on early contrast media dynamics.

Aorta↗

PubMed2001

Acute colonic diverticulitis: visualization in magnetic resonance imaging.

The incidence of acute colonic diverticulitis (ACD) is increasing. To allow rational therapeutic decisions to be made, a timely diagnosis is required. The feasibility of "on-admission-MRI" to establish the diagnosis has not yet been studied. Therefore, a prospective observational study was carried out in 20 patients with an established diagnosis of ACD. The diagnostic criteria for the MRI diagnosis of ACD were the demonstration of at least one diverticulum, pericolic exudation, and edema of the colonic wall. MRI was diagnostic in all but one patient. It is concluded that MRI has considerable diagnostic potential in ACD and should be formally evaluated.

Acute Disease↗

PubMed2001

Prospective comparison of MR phase-contrast velocimetry with intravascular doppler US during infrainguinal artery angioplasty.

PURPOSE: To evaluate the accuracy of magnetic resonance (MR) velocimetry for quantitative assessment of stenosis in patients undergoing percutaneous transluminal angioplasty (PTA). MATERIALS AND METHODS: Thirty patients underwent PTA of the infrainguinal region. To assess hemodynamic parameters of lesions, MR phase-contrast velocimetry with a circular-polarized extremity receiver coil and a cardiac gated gradient echo sequence was conducted before and 1 day after PTA. Additionally, all lesions were examined by means of intravascular Doppler flow measurements (0.018-inch wire, 12 MHz). From these data, the degree of stenosis was calculated and a comparison of MR velocimetry with intravascular Doppler US was undertaken. RESULTS: Correlation between calculated grade of stenosis for MR velocimetry and intravascular Doppler US was good and significant (r = 0.74; P <.001). Calculated luminal stenosis grade were similar for both methods before PTA (intravascular Doppler US: 0.62 +/- 0.18, MR velocimetry: 0.54 +/- 0.19; P =.17 with paired Student t-test) and after PTA (0.25 +/- 0.23 and 0.3 +/- 0.2, respectively; P =.56). CONCLUSION: MR velocimetry results in reliable noninvasive in vivo flow measurements and allows accurate assessment of stenosis in a clinical setting.

Aged↗

PubMed2001

In vivo evaluation of an intravascular receiver coil for MRI at 1.0 Tesla.

BACKGROUND: Evaluation of the applicability of intravascular radiofrequency receiver coils by means of a pig in-vivo-experiment for the detection of vessel wall structures at 1.0 Tesla. MATERIALS AND METHODS: The intravascular receiver coil was constructed according to a well evaluated single-loop-design, which was mounted onto a balloon catheter for angioplasty. Under fluoroscopy control the balloon catheter was placed in the common carotid artery of a porcine. Images were obtained in a 1.0 Tesla clinical scanner using a fast-spin-echo-, a gradient-echo- and a high resolution spin-echo-sequence. Histological examinations were obtained to detect any vessel wall damage associated with the use of the receiver coil. RESULTS: High quality images with a resolution up to 0.16*0.12 mm2 could be acquired in aquisition times of about 5 minutes. Subtle intra- and extra-vascular structures such as the balloon, irregularities of the vessel wall or bordering structures could be visualized. The histological examination showed no vessel damage due to the application of the intravascular receiver coil. CONCLUSIONS: The application of intravascular receiver coils for the visualization of the vessel wall is feasible at 1.0 Tesla without histologically detectable trauma to the vessel wall.

Animals↗

PubMed2001

[Molecular radiology. II: Molecular imaging].

The most important strategies for molecular imaging are presented. Processes can now be imaged in vitro and in vivo at the molecular level with the help of modern procedures such as SPECT, PET, MRI, and highly developed optical methods. The ability to view the expression of genes, the pharmacokinetics of gene therapy vectors, of therapeutic DNA, and of classical pharmacons in vivo opens up completely new perspectives for the research on, diagnosis of, and therapy for diseases. The current status of these developments are described, potential fields of use and possibilities for further development are outlined.

Diagnostic Imaging↗

PubMed2001

Multiplanar reconstructions and three-dimensional imaging (computed rotational osteography) of complex fractures by using a C-arm system: initial results.

With use of a calibrated angiographic C-arm system and a postprocessing workstation, the authors acquired volume data sets from two-dimensional digital projection images obtained during a C-arm rotation around the patient axis. Multiplanar reconstruction and three-dimensional images of complex fractures were reconstructed and compared with spiral computed tomographic studies in a cadaveric pig study and in eight patients. Computed rotational osteography provided high-resolution multiplanar reconstruction and three-dimensional images of complex fractures.

Animals↗

PubMed2001

MR hydrometry to assess exocrine function of the pancreas: initial results of noninvasive quantification of secretion.

PURPOSE: To evaluate magnetic resonance (MR) hydrometry, a method of quantifying fluid amounts by using MR imaging, for assessing the exocrine function of the pancreas after stimulation with secretin. MATERIALS AND METHODS: Images were obtained with a single-shot turbo spin-echo sequence by using a 1.0-T magnet with a quadrature body coil. Image postprocessing and evaluation were performed at an external workstation by using a specially designed histogram algorithm that translates the MR signal intensity of duodenal filling into an actual amount of duodenal fluid. This algorithm was tested in vitro and in vivo. Finally, MR hydrometry results in five patients were correlated with those of the secretin-cerulein test. RESULTS: The phantom measurements showed a high correlation (r = 0.99) between the actual amount of fluid in the imaging volume and the calculated results. In vivo, the ability of MR hydrometry to enable exact quantification of fluid amounts was demonstrated. In correlating the signal intensity of duodenal filling with the exact amount of additional fluid in the duodenum in volunteers, a coefficient of 0.043 gray tones per pixel per milliliter was calculated. The correlation (r) between secretin-stimulated duodenal fluid output estimated by using tube aspiration and that estimated by using MR hydrometry was 0.946 (P <.05). CONCLUSION: MR hydrometry is a promising noninvasive method of assessing fluid output as a measure of exocrine pancreatic function.

Algorithms↗