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Biomedical subjects

B Hamm

Publications and source records attributed to B Hamm.

At least 91 records · Page 5Linked to original sources
PubMed2001

Three-dimensional gadolinium-enhanced magnetic resonance venography in suspected thrombo-occlusive disease of the central chest veins.

STUDY OBJECTIVE: To determine the usefulness of high-resolution three-dimensional (3D) gadolinium-enhanced magnetic resonance venography (MRV) in the evaluation of central venous thrombo-occlusive disease of the chest. DESIGN: Prospective study. SETTING: University hospital. PATIENTS: Sixteen consecutive patients with clinically suspected thrombosis of the superior vena cava, subclavian, brachiocephalic/innominate, internal jugular, or axillary veins. Thirteen patients had a neoplasm, two patients had a connective tissue disease, and one patient had a history of strenuous exercise. Twelve of 16 patients had prior central venous catheter placement. MRI was correlated with color-coded duplex sonography (CCDS) in 7 of 16 patients, digital subtraction angiography (DSA) in 3 of 16 patients, and CT in 2 of 16 patients. INTERVENTION: Contrast-enhanced MRV was performed in a total of 20 examinations. A 3D data set (gradient echo; time to repeat, 4.6 ms; time to echo, 1.8 ms; flip angle, 30 degrees; time of acquisition, 23 s; 512 matrix/64 partitions; slice thickness, 1.5 mm) was acquired in the arterial and venous phase. Overall image quality was assessed on a 5-point scale. The presence, site, and extent of thrombus, as well as presence of an intravascular device, were determined. MEASUREMENTS AND RESULTS: Overall image quality was rated very good (1 point) in 7 of 16 cases (44%) and good (2 points) in 9 of 16 cases (56%). Thrombus was detected in 16 of 16 patients, and complete extent of disease could be determined in 15 of 16 patients (94%). MRV did not miss any finding obtained by CCDS, DSA, or CT, and provided additional information in 6 of 16 examinations (38%). CONCLUSION: Contrast-enhanced MRV is a fast and reliable noninvasive procedure with excellent results regarding detection and determination of the extent of thrombo-occlusive disease of the chest veins.

Adult↗
PubMed2001

Magnetic resonance imaging of stentless xenografts for reconstruction of right ventricular outflow tract.

The objective was to overcome allograft shortage during the Ross operation; stentless xenografts were carefully evaluated for hemodynamic behavior and valve deterioration during medium term follow-up. Between January 10, 1994 and January 4, 1996 nine adult patients (age 31-51 years) underwent aortic valve replacement with an autologous pulmonary valve and right ventricular outflow tract reconstruction with the Edwards Prima or Medtronic Freestyle xenograft. One patient was dead early and one late, both from noncardiac reasons. Forty-eight to 66 months follow-up was available for 7 patients and was performed with physical examination in the outpatient clinic, transthoracic echocardiography (TTE), and magnetic resonance imaging (MRI). Two patients received 29-mm valves and the remaining 27-mm valves. No reoperation became necessary during follow-up. Preoperative left ventricular ejection fraction ranged from 20% to 84%, median 61%, mean 59% +/- 18%. At latest follow-up left ventricular ejection fraction was 49% to 70%, median 57%, mean 58% +/- 8%. TTE showed no calcification of the xenograft wall or cusps. MRI revealed good autograft function with no evidence of stenosis in any patient. Four patients showed no and three trivial regurgitation. Right ventricular outflow tract-stenosis could not be seen in any patient. Calculated gradients of the xenograft valves ranged from 2 to 6 mm Hg, median 3 mm Hg (mean 3.1 +/- 2.4 mm Hg) and calculated EOA ranged from 2.0 to 4.0 cm(2), median 2.8 cm(2). MRI supported these findings and showed pliable xenograft cusps in all patients. Right ventricular function was well preserved in all patients. In adult patients right ventricular outflow tract reconstruction with stentless xenografts can be performed safely and intermediate-term results are encouraging. During medium-term (5-7 years) follow-up no calcification or deterioration of valve function occurred with excellent hemodynamic behavior.

Adult↗
PubMed2000

Age-related blood half-life of particulate contrast material: experimental results with a USPIO in rats.

It has been well established in the literature that phagocytic activity in animals and humans changes with age, but this phenomenon has not yet been investigated for particulate contrast agents. The present study was therefore performed to determine the effect of age on blood half-life of a superparamagnetic iron oxide blood pool contrast agent and on the velocity of its uptake in the liver and spleen of the rat by means of magnetic resonance (MR) imaging. A total of 18 rats (group A: 214-255 g, age: 45-50 days; group B: 432-563 g, age: 100-120 days) were imaged at 1.5 T using a 3D gradient-recalled echo (GRE) sequence (TR/TE 6.6/2.3 msec; alpha 25 degrees, frontal). Images were acquired before and every 3-5 minutes for up to 30 minutes after i.v. injection of 30 micromol Fe/kg of a citrate-coated superparamagnetic iron oxide-based contrast agent (VSOP-C43). Intravenous injection of VSOP-C43 resulted in a pronounced initial signal enhancement in vessels, which decreased with a half-life of 8.4 +/- 0.9 minutes in group A and of 15.9 +/- 2. 4 minutes in group B (P < 0.01). The half-life of signal decrease was 11.6 +/- 2 minutes and 19.9 +/- 4.4 minutes in the liver (P < 0. 01) and 19.6 +/- 3.1 minutes and 26.7 +/- 5.2 minutes in the spleen (not significant). The results show that the age-related phagocytic activity has a significant effect on the circulation time and velocity of uptake of a particulate MR imaging contrast agent. This fact must be taken into consideration in both the preclinical and clinical development of particulate contrast material and in the clinical application of such agents.

Age Factors↗
PubMed2000

New generation of monomer-stabilized very small superparamagnetic iron oxide particles (VSOP) as contrast medium for MR angiography: preclinical results in rats and rabbits.

The purpose of this study was to evaluate the signal enhancement characteristics of very small superparamagnetic iron oxide particles (VSOP)-C63, a new monomer-coated, iron oxide-based magnetic resonance (MR) blood pool contrast medium with a very small particle size and optimized physical properties. Equilibrium MR angiography (MRA) of rats (thoracic and abdominal vessels) was performed at 1.5 T with a three-dimensional gradient-recalled echo (3D GRE) technique (TR/TE 6.6/2.3 msec, flip angle 25 degrees ) before and after (every 3-5 minutes up to 50 minutes) i.v. injection of VSOP-C63 [dosages: 15, 30, 45, 60, 75, and 90 micromol Fe/kg; diameter: 8 nm; relaxivities at 0.47 T: R1 = 30 l/(mmol * s); R2 = 39 l/(mmol * s)]. First-pass MRA images (3D-GRE, TR/TE 4.5/1.7 msec, flip angle 25 degrees ) were obtained with 45 micromol Fe/kg VSOP-C63 in comparison with 0.2 mmol Gd/kg of gadolinium diethylene triamine pentaacetic acid (Gd DTPA; before and every 5 seconds p.i.). MRA (3D GRE, TR/TE 4.5/1.7 msec, flip angle 25 degrees) of coronary vessels in rabbits was performed after i.v. injection of 45 micromol Fe/kg of VSOP-C63. In rats maximal S/N ratio in thoracic and abdominal arteries directly after i.v. injection of VSOP-C63 was 25 +/- 1, 43 +/- 2, 49 +/- 4, 57 +/- 3, 64 +/- 3, and 63 +/- 3 for the different dosages. Blood half-life was dose dependent (15 +/- 2, 20 +/- 3, 29 +/- 6, 37 +/- 5, 61 +/- 16, and 86 +/- 21 minutes). At a dose of 30 micromol Fe/kg even small intrarenal arteries were sharply delineated. First-pass MRA showed no significant difference in the S/N ratio between Gd-DTPA (71.5 +/- 11.5) and VSOP-C63 (65.1 +/- 18. 3). The proximal segments of the coronary arteries in rabbits were clearly depicted at a dose of 45 micromol Fe/kg. The monomer-coated, iron oxide-based contrast medium VSOP-C63 exhibits favorable properties as a blood pool agent for both equilibrium and first-pass MRA. J. Magn. Reson. Imaging 2000;12:905-911.

Animals↗
PubMed2000

MR imaging in posthysterectomy vaginal prolapse.

In the diagnostic work-up of vaginal prolapse after hysterectomy cystoceles can be identified by sonography, whereas enteroceles and rectoceles can only be suspected in a routine clinical setting. The present pilot study was undertaken to investigate the diagnostic role of magnetic resonance imaging (MRI) in the differentiation of cysto-, entero- and rectoceles in women with posthysterectomy vaginal prolapse. Thirteen women (mean age 61, SD +/- 7 years) with posthysterectomy vaginal prolapse underwent MRI (Gyroscan S 15, Philips). A median sagittal image series was obtained with a gradient-echo sequence, fast field echo, both at rest and during Valsalva maneuvers. MRI allowed the identification of cysto-, entero- and rectoceles, and differentiation between entero- and rectoceles in cases with inconclusive clinical findings. These findings make dissection more reliable and improve the outcome of hernia repair. No additional diagnostic information is obtained with MRI compared to ultrasound in the assessment of cystoceles.

Aged↗
PubMed2000

MR imaging of septic sacroiliitis.

OBJECTIVE: To investigate the diagnostic value of magnetic resonance (MR) imaging in detecting septic sacroiliitis and to determine whether the MR characteristics allow this entity to be differentiated from sacroiliitis in spondylarthropathy (SpA). PATIENTS AND DESIGN: The imaging findings of 11 patients with septic sacroiliitis were retrospectively analyzed by two experienced radiologists. Radiographic surveys of the pelvis as well as computed tomography (CT) and MR images of the sacroiliac joints were available in all cases. Seven of the patients additionally underwent a follow-up MR examination. The MR imaging protocol comprised combinations of coronal and transverse T1-weighted spin-echo (SE) or fast SE sequences, T2-weighted gradient-echo (GE) sequences and short tau inversion recovery sequence (STIR) sequences as well as dynamic contrast-enhanced T1-weighted acquisitions. RESULTS: Three patients with a short disease history showed anterior and/or posterior subperiosteal infiltrations ("lava cleft phenomenon"), transcapsular infiltrations of juxtaarticular muscle layers, which obscured the fasciae, and periarticular bone marrow edema. The eight patients with more advanced stages of sacroiliitis additionally showed abscess formation, sequestration, and erosion. At follow-up MR examination (n=7) under systemic antibiotic treatment, the morphologic characteristics showed progression (n=1), regression (n=4), unchanged findings (n=1), or a mixed response (n=1). Clinical improvement precedes resolution of the MR findings. CONCLUSIONS: Anterior and/or posterior subperiosteal infiltrations and transcapsular infiltrations of juxtaarticular muscle layers were depicted in all patients. These MR imaging findings are characteristic of septic sacroiliitis and may be used to differentiate this entity from sacroiliitis in SpA.

Adolescent↗
PubMed2000

Multifocal nodular fatty infiltration of the liver mimicking metastatic disease on CT: imaging findings and diagnosis using MR imaging.

The aim of this study was to describe the MR appearance of multifocal nodular fatty infiltration of the liver (MNFIL) using T1-weighted in-phase (IP) and opposed-phase (OP) gradient-echo as well as T2-weighted turbo-spin-echo sequences with fat suppression (FSTSE) and without (HASTE). Magnetic resonance imaging examinations at 1.5 T using T1-weighted IP and OP-GRE with fast low angle shot (FLASH) technique, and T2-weighted FSTSE, T2-weighted HASTE of 137 patients undergoing evaluation for focal liver lesions were reviewed. Five patients were identified in whom CT indicated metastatic disease; however, no liver malignancy was finally proven. Diagnosis was confirmed by biopsy (n = 3), additional wedge resection (n = 1) or follow-up MRI 6-12 months later (n = 5). Regarding the identified five patients, the number of focal liver lesions was 2 (n = 2) and more than 20 (n = 3). The MR imaging characteristics were as follows: OP-image: markedly hypointense (n = 5); IP image: isointense (n = 2) or slightly hyperintense (n = 3); T2-weighted FSTSE-image: isointense (n = 5); T2-weighted HASTE image isointense (n = 1); slightly hyperintense (n = 4). On OP images all lesions were sharply demarcated and of almost spherical configuration (n = 5). Further evaluation by histology or follow-up MR imaging did not give evidence of malignancy in any case. Histology revealed fatty infiltration of the liver parenchyma in three patients. Magnetic resonance follow-up showed complete resolution in two patients and no change in three patients. Multifocal nodular fatty infiltration can simulate metastatic disease on both CT and MR imaging. The combination of in-phase (IP) and opposed-phase (OP) gradient-echo imaging can reliably differentiate MNFIL from metastatic disease.

Aged↗
PubMed2000

Tissue transition projection (TTP) of the intestines.

Tissue transition projection (TTP) represents a three-dimensional reconstruction technique for volumetric image data sets. To demonstrate the principle characteristics of TTP, a simple phantom consisting of two pipes with a simulated, wall-adherent polyp was scanned with spiral CT, and images were reconstructed by means of volume rendering for both opaque surface reconstructions and TTP. Tissue transition projection was used in 7 patients for reconstruction of the small intestine or the colon. Unlike three-dimensional reconstructions with opaque surfaces, TTP enhances surface transitions while suppressing homogeneous areas, allowing delineation of the bowel wall similar to conventional double-contrast studies.

Adenocarcinoma↗
PubMed2000

Colonography using multislice CT.

Computed tomography (CT) represents the preferred imaging modality for imaging the large bowel when virtual endoscopic reconstructions are desired. Using the spiral acquisition technique, it has become possible to scan the entire abdomen within a single breathhold, however, slice thicknesses of 5 mm or more are necessary should the breathhold not last longer than 30-40 s. With the advent of multislice CT, contiguous 1-mm slices can be obtained through the entire abdomen while even shortening the breathhold to 25-30 s. The improved speed and spatial resolution of multislice CT results in remarkably sharp virtual reconstructions allowing detection of polyps with sizes less than 3 mm. The disadvantages must still be considered including a dataset consisting of up to 800 images representing a new challenge for postprocessing hard- and software.

Colon↗
PubMed2000

Pharmacokinetic analysis of glioma compartments with dynamic Gd-DTPA-enhanced magnetic resonance imaging.

Dynamic contrast-enhanced magnetic resonance imaging (MRI) is widely used for measuring perfusion and blood volume, especially cerebral blood volume (CBV). In case of blood-brain barrier (BBB) disruption, the conventional techniques only partially determine the pharmacokinetic parameters of contrast medium (CM) exchange between different compartments. Here a modified pharmacokinetic model is applied, which is based on the bidirectional CM exchange between blood and two interstitial compartments in terms of the fractional volumes of the compartments and the vessel permeabilities between them. The evaluation technique using this model allows one to quantify the fractional volumes of the different compartments (blood, cells, slowly and fast enhancing interstitium) as well as the vessel permeabilities and cerebral blood flow (CBF) with a single T1-weighted dynamic MRI measurement. The method has been successfully applied in 25 glioma patients for generating maps of all of these parameters. The fractional volume maps allow for the differentiation of glioma vascularization types. The maps show a good correlation with the histological grading of these tumors. Furthermore, regions with enhanced interstitial volumes are found in high-grade gliomas. Differences in permeability maps of Gd-DTPA apart from BBB disruption do not exist between different tissue types. CBF measured in high-grade glioma is less pronounced than it would be expected from their blood volume. Therefore pharmacokinetic imaging provides an additional tool for glioma characterization.

Adolescent↗
PubMed2000

[Initial clinical experiences with digital full-field mammography].

OBJECTIVE: Digital full-field mammography has been used at the Department of Radiology of Charité Medical Center in Berlin since June 1999. This study compares the new digital technique with conventional mammography including a survey of its value in breast imaging and an outline of future prospects. MATERIAL AND METHODS: More than 1,000 of a total of over 5,000 mammographies performed between June 1999 and April 2000 have been obtained using the digital full-field mammography system Senographe 2000D (GE Medical Systems). The digital mammograms were compared with previous conventional films and conventional mammographies performed during the same period (Philips UC Diagnost, Senographe DMRplus). RESULTS: Digital mammographies were equal to conventional ones in all cases and seemed to be superior in detecting microcalcifications in dense glandular tissue. Adequate assessment was possible despite the lower spatial resolution compared to conventional mammography. Additional magnified images were obtained with both techniques for differentiating microcalcifications. CONCLUSIONS: Digital full-field mammography appears to be at least equal to the conventional technique and even superior in some respects. In our experience, the lower spatial resolution of digital mammography has no major disadvantages. The digital system provides new options for electronic storage of mammograms, telemammography, and computer-aided diagnosis.

Breast Neoplasms↗
PubMed2000

[Value of negative oral contrast media in MR cholangiopancreatography (MRCP)].

PURPOSE: Evaluation of the use of a negative oral contrast material in MR cholangiopancreatography (MRCP). MATERIAL AND METHODS: We performed MRCP in single-shot technique (TSE, TR = 2800 ms, TE = 1100 ms, ETL = 64) in 38 patients before and 20-30 min after oral administration of 300-600 ml of a negative oral contrast material. The visualization ducts and details important for the diagnosis was evaluated in a blinded manner. Ductal diameters were measured. Both sets of images were evaluated qualitatively. RESULTS: The ductal diameters did not change after administration of oral contrast material. In 1/3 of all cases the ductal structures were superimposed by a high signal intensity of fluid in the gastrointestinal tract, especially in the tail of the pancreas. After administration of oral contrast material only in 3 patients could a complete visualization of the ducts not be achieved. In 5 cases, details relevant for the diagnostic decision could be seen only on post-contrast images. The anatomic orientation was not compromised by the absence of signal in the gastrointestinal tract. CONCLUSION: Negative oral contrast material should be given before performing a MRCP to provide non-superimposed visualization of the bile and pancreatic ducts. There is no negative influence of the oral contrast material on the diameter of the ducts.

Administration, Oral↗
PubMed2000

[Determination of left ventricular function parameters and myocardial mass: comparison of MRI and EBT].

PURPOSE: Comparative volumetric assessment of the left ventricle by magnetic resonance imaging (MRI) and electron beam tomography (EBT) in patients with ischemic and dilated cardiac disease. METHODS: Thirty-two patients underwent cine MRI and EBT in the multislice mode. All studies were triggered to the ECG. Left ventricular ejection fraction (EF), end-diastolic (EDV) and end-systolic volume (ESV), and myocardial mass (MM) were determined by 3D-volumetry by MRI and EBT and results were compared. RESULTS: The correlation between MRI and EBT for EF, EDV, ESV, and MM were r = 0.86, r = 0.95, r = 0.95, and r = 0.93, respectively. CONCLUSIONS: There is an excellent correlation between MRI and EBT in determining left-ventricular parameters. Both methods are suitable for volumetric assessment of the left ventricle.

Adult↗
PubMed2000

[The staging of bladder tumors in MRT: the value of the intravesical application of an iron oxide-containing contrast medium in combination with high-resolution T2-weighted imaging].

AIM: To investigate superparamagnetic iron oxide (SPIO) particles as intravesically applied contrast material in combination with high-resolution T2-weighted MR imaging for the diagnostic assessment of urinary bladder tumors. METHODS: A prospective study was performed in 40 patients with suspected urinary bladder tumors who underwent MR imaging with a body phased-array coil at 1.5 T. Prior to imaging, a SPIO-containing solution (179.2 mg Fe/l) was instilled into the bladder. All patients were examined with T2-weighted, half-fourier acquired single shot turbo spin echo sequences and T1-weighted fast low angle shot sequences in 3 planes as well as a T2-weighted turbo spin echo sequence (TSE) using a 512 matrix. An additional gadolinium-enhanced dynamic study was performed in 33 patients. All patients underwent transurethral resection of the bladder or cystectomy. RESULTS: The combination of intravesically applied SPIO particles and a high-resolution T2-weighted TSE sequence depicted intravesical tumors as small as 4 mm. A reliable identification of the different layers of the bladder wall was possible in 5 cases only. The T2-weighted TSE sequence allowed the correct determination of the depth of infiltration in 29 of 36 patients with urothelial cancer by assessing the inner and outer boundary of the urinary bladder wall. This sequence had a diagnostic accuracy of 81% compared to 84% for the dynamic study (26/31). CONCLUSION: Even small tumors could be identified with the T2-weighted TSE sequence after intravesical administration of SPIO particles but it was not possible to reliably differentiate the layers of the bladder wall. The results suggest that a dynamic MR imaging study cannot be dispensed with in patients with urinary bladder cancer.

Administration, Intravesical↗
PubMed2000

[MRI of the prostate after combined radiotherapy (afterloading and percutaneous): histopathologic correlation].

AIM: To identify the MRI changes of the prostate after combined (high-dose rate interstitial with external beam) radiotherapy for, localized prostate cancer and to correlate the findings with histology in order to determine the value of MR imaging in the follow-up of these patients. MATERIAL AND METHODS: Twenty-three patients underwent MR imaging at 1.5 T between 6 and 24 months after completion of combined radiotherapy. The prostate was imaged with axial and coronal T2-weighted sequences and axial T1-weighted sequences before and after intravenous administration of Gd-DTPA. Quadrant or sextant biopsy was performed in all cases and three patients with proven persistence of the tumor underwent salvage prostatectomy. The MRI findings were compared with the biopsy results or the large-area sections. RESULTS: On T2-weighted images the fibrotically changed peripheral zone was hypointense while persistent tumor tissue showed hyperintensity. Solid tumors were depicted when they had a diameter of 1 cm or more. Persistent tumors of the diffuse multifocal type escaped detection. Contrast-enhanced T1-weighted imaging yielded no additional information. The accuracy in detecting persistent tumor was 74%. CONCLUSIONS: Histopathologic changes seen after combined radiotherapy correlate with the findings on T2-weighted MR images. MR imaging cannot replace follow-up by routine biopsy. Its only role is assessing local operability in cases found to have increasing PSA levels during follow-up. Further studies are needed to determine the role of MR imaging in this patient population.

Adult↗