Biomedical subjects

M Deimling

Publications and source records attributed to M Deimling.

At least 37 records · Page 2Linked to original sources

PubMed1996

Solitary pulmonary nodules: MR evaluation of enhancement patterns with contrast-enhanced dynamic snapshot gradient-echo imaging.

PURPOSE: To evaluate the enhancement patterns of solitary pulmonary nodules (SPNs) with dynamic contrast-material-enhanced magnetic resonance (MR) imaging to differentiate between benign and malignant SPNs. MATERIALS AND METHODS: Twenty-eight patients with SPNs 30 mm or smaller in diameter were examined with pre- and postcontrast, electrocardiographically gated, T1-weighted spin-echo (SE) sequences and a snapshot gradient-echo (GRE) sequence after bolus injection of a paramagnetic contrast agent. For all SPNs (20 malignant, eight benign), the percentage increase in signal intensity (%SI) on the postcontrast T1-weighted SE images and the enhancement curves (%SI/sec) for the snapshot GRE measurements were established from regions of interest. RESULTS: Malignant nodules showed a higher increase of signal intensity during the first transit of the bolus of contrast material on the dynamic snapshot GRE images (malignant: median, 18.1 %SI/sec; range, 6.7-95.2 %SI/sec; benign: median, 2.3 %SI/sec; range, 0.1-8.1 %SI/sec) (P < .0001). Static T1-weighted SE measurements did not allow differentiation between malignant (median, 53.4 %SI; range 12.5-110.0 %SI) and benign (median, 33 %SI; range, 0.8-85.5 %SI) (P > .2) nodules on the basis of the degree of contrast enhancement. CONCLUSION: Dynamic contrast-enhanced MR measurements of tumor enhancement can provide additional information about the nature of SPNs.

Adult↗

PubMed1995

Ultra-rapid gradient echo imaging.

A novel ultra-rapid gradient echo (URGE) NMR imaging technique is introduced, which is capable of continuous high resolution 3D scanning while neither subject to fast gradient switching nor excessive RF power deposition. Sampling free induction decays instead of creating spin echoes enables maintaining a workable steady state magnetization. Due to segmented k-space acquisition, chemical shift, diffusion, and field inhomogeneity effects do not present major problems. We report on implementations acquiring from 32 x 64 x 64 partial-Fourier image sets in 0.72 s, allowing for single-shot magnetization-prepared 3D imaging, to 128 x 128 x 128 image sets in 13.3 s and 21.5 s on a standard MRI scanner.

Artifacts↗

PubMed1995

High-resolution magnetic resonance imaging of the endolymphatic duct and sac.

An anatomical study was carried out to determine the extent to which magnetic resonance imaging (MRI) could delineate inner ear structures. Anatomical preparations of human petrous temporal bone were examined and compared with the results of MRI in 20 healthy subjects to see whether the structures of the inner ear could be visualized. Imaging of the subjects was carried out in a 1.0-T MRI scanner (Siemens Magnetom Impact). Two strongly T2*-weighted sequences were used: a 3D-PSIF sequence and a 3D-CISS sequence. The 3D data sets were postprocessed using a Maximum Intensity Projection (MIP) program. Our investigations show that it is possible to obtain accurate visualization of structures with a diameter of under 1 mm. In all 20 subjects it was possible to identify both the endolymphatic duct and the endolymphatic sac.

Adult↗

PubMed1995

T2-weighted breath-hold MR imaging of the liver at 1.5 T: results with a three-dimensional steady-state free precession sequence in 87 patients.

PURPOSE: To evaluate a fast three-dimensional (3D) sequence that permits the acquisition of 16 T2-weighted images within a 29-second breath hold for magnetic resonance (MR) imaging of the liver. MATERIALS AND METHODS: Eighty-seven patients with focal liver lesions were examined at 1.5 T by using a 3D reversed fast imaging with steady-state precession (PSIF) sequence at flip angles of 15 degrees, 30 degrees, and 70 degrees and a T2-weighted spin-echo (SE) sequence. Quantitative and qualitative image analysis was performed. RESULTS: Contrast and signal difference-to-noise ratios were 56% and 33% (liver-spleen) and 76% and 68% (liver-tumor), respectively, with the 3D-PSIF sequence compared with the T2-weighted SE sequence. With 3D-PSIF, overall image quality was poorer than that of the T2-weighted SE sequence at flip angles of 15 degrees but was similar at 30 degrees and 70 degrees. At low flip angles (15 degrees and 30 degrees) all lesion types were hyperintense. At a flip angle of 70 degrees, it was predominantly cysts and hemangiomas that showed high signal intensity. With the 3D-PSIF sequence, intrahepatic vessels are void of signal and can be better distinguished from small liver lesions compared with the flow-compensated T2-weighted SE sequence. CONCLUSION: The fast 3D-PSIF sequence is a valuable addition to MR imaging of the liver.

Adult↗

PubMed1995

Malignant liver tumors treated with MR imaging-guided laser-induced thermotherapy: technique and prospective results.

PURPOSE: To evaluate magnetic resonance (MR) imaging-guided laser-induced thermotherapy (LITT) of liver metastases. MATERIALS AND METHODS: In a phase II study, 20 patients with 33 metastases from colorectal carcinoma (75%) or other primary tumors (25%) underwent LITT. MR thermometry performed with fast low-angle shot sequences was used to monitor therapy on-line, and dynamic and static contrast material-enhanced MR images enabled estimation of the degree of resultant necrosis. Follow-up studies were performed 3 months after thermotherapy. RESULTS: The thermosequences enabled accurate on-line monitoring in 85% of lesions. In 69% of lesions 20 mm in diameter or smaller, contrast-enhanced MR images depicted substantial necrosis, with a local tumor control rate of 69% after 6 months and 44% after 12 months. Among lesions larger than 20 mm, necrosis was frequently incomplete, with a local control rate of only 41% after 6 months and 27% after 12 months. CONCLUSION: MR imaging-guided LITT of liver metastases is a safe and promising therapy for liver metastases.

Adult↗

PubMed1995

Recurrent nasopharyngeal tumors: preliminary clinical results with interventional MR imaging--controlled laser-induced thermotherapy.

PURPOSE: To evaluate magnetic resonance (MR) imaging-controlled laser-induced thermotherapy (LITT) in the treatment of recurrent head and neck tumors. MATERIALS AND METHODS: Six patients with recurrent nasopharyngeal tumors (squamous cell carcinoma [n = 4], pleomorphic adenoma [n = 2]) underwent LITT with local anesthesia. A 7-F introducing sheath was inserted into the center of the tumor followed by a specially designed laser emitter. Therapy was monitored on-line with MR thermometry, and the amount of necrosis was estimated with dynamic and static contrast material-enhanced sequences. RESULTS: All procedures were well tolerated with use of local anesthesia, with no clinically relevant side effects. MR thermometry depicted up to 15-mm-diameter areas of less signal intensity near the laser tip. Coagulative necrosis was achieved in all patients (volume range, 4-28 cm3), and clinical symptoms were reduced in four. CONCLUSION: MR imaging-controlled LITT may be a safe, minimally invasive alternative in the treatment of recurrent head and neck tumors.

Adenoma, Pleomorphic↗

PubMed1994

[Fat suppression in contrast-enhanced MRT of the base of the skull and of the head-neck area: its clinical value].

167 patients with abnormalities at the skull base and at the cervical-skull junction were examined by MRT in order to compare a FATSAT technique with T1- and T2-weighted SE sequences before and after intravenous injection of 0.1 mmol Gd-DTPA/kg KG. The diagnostic information from corresponding FATSAT and T1-SE sequences was correlated with the histopathological findings. In 10.7% of patients fat suppression was inadequate and in a further 11.3% of patients chemical shift artifacts limited the diagnostic value. The number of detectable lesions was not increased by the use of FATSAT sequences but visualisation of soft tissue lesions was improved, adding to the diagnostic value under specific conditions. Evaluating by the Friedman and Wilcoxon test showed that the postcontrast FATSAT sequences were markedly superior (p < 0.01) in delineating and contrasting the lesions. The additional use of contrast enhanced FATSAT sequences resulted in improved diagnosis of lesions at the skull base and the facial skeleton.

Adipose Tissue↗

PubMed1994

Magnetic resonance imaging-controlled laser-induced interstitial thermotherapy.

RATIONALE AND OBJECTIVES: Laser-induced interstitial thermotherapy (LITT) may become an attractive modality for minimally invasive tumor therapy. Magnetic resonance imaging (MRI) could be used to assist this procedure. METHODS: A T1-weighted turbo fast low-angle shot (FLASH) sequence for on-line monitoring of the laser-influenced region (liver, muscle) was investigated. Sequence parameters were optimized for maximal image contrast. Magnetic resonance imaging-controlled LITT was performed in vitro, in vivo (rabbits), and in 8 human investigations (6 patients). Special laser applicators were used to establish a uniform laser light distribution. RESULTS: With the MRI sequence used, the LITT region is visualized as a bright area outlined by a dark border. This dark border corresponds to an isotherm of 45 +/- 2 degrees C depending on the sequence parameters used. CONCLUSION: With the T1-weighted turbo-FLASH sequence, MRI can be used for on-line monitoring of interstitial laser-induced thermotherapy in moving organs.

Aged↗

PubMed1993

QUEST--a quick echo split NMR imaging technique.

A novel millisecond NMR imaging method is introduced, which generalizes the principle of stopped-pulse experiments. It has been dubbed QUEST for QUick Echo Split imaging Technique. Repeated dephasing and excitation is used to divide a primary free induction decay into an exponentially growing number of echoes. Very few gradient lobes and RF pulses already generate large numbers of echoes, so neither gradient switching speed nor RF absorption represents any real limitation. True spin echoes are easily produced.

Brain↗

PubMed1993

Preliminary evaluation: magnetic resonance of urography using a saturation inversion projection spin-echo sequence.

A saturation inversion projection (SIP) spin-echo technique is reported which allows a reliable direct visualization of the urogenital system as well as its functional performance in magnetic resonance imaging. We used an imaging sequence with a 90 degree saturation pulse and two 180 degree inversion pulses followed by a short spin-echo (SE) pulse sequence. The three time intervals in the 90 degree-180 degree-180 degree-SE pulse train were adjusted to suppress the signals of soft tissues and fat. After intravenous injection of the contrast agent Gd-DTPA, a shortening of the kidney T1 and the T1 of the urogenital system is obtained below the T1 values of fat and soft tissues, and these remaining ultra-short T1 tissues were imaged with the SIP sequence. Using a sequential measuring technique a quantitative evaluation of the glomerular filtration rate seems to be possible with a time resolution of 18 sec per image. In addition, magnetic resonance urography using the SIP sequence provided a good visualization of the urogenital system and may show several clinical utilities in further clinical studies.

Contrast Media↗

PubMed1992

Breath-hold T2-weighted sequences of the liver: a comparison of four techniques at 1.0 and 1.5 T.

T2-weighted images are considered the most sensitive for lesion detection at high field; however, long imaging time is problematic. Accordingly, the authors compared four breath-hold T2 or T2* weighted sequences comprising T2*-weighted FLASH, T2*-weighted PSIF, T2-weighted rapid spin echo (RASE), and T2-weighted Turbo-FLASH (Turbo) in 20 different healthy volunteers, 10 at 1.0 T and 10 at 1.5 T with reference to regular T2-weighted spin echo. Images were evaluated quantitatively by liver signal to noise (S/N) and spleen-liver signal difference to noise (SD/N) ratios and qualitatively for presence of artifacts and image quality. Data were evaluated for 1.0 T and 1.5 T separately and combined. In the combined evaluation, T2*-FLASH had good S/N (23.1 + 5.1) but low SD/N (2.9 + 1.7) and suffered from susceptibility artifacts. T2* PSIF had good S/N (28.1 + 10.0) and moderate SD/N (6.0 + 2.4), but occasionally had heterogeneous signal intensity. Flow signal void was an attractive feature. T2 RASE had very low S/N (4.4 + 1.9) and low SD/N (2.3 + 1.1) and suffered from flow artifacts. T2-Turbo had good S/N (24.6 + 8.6) and SD/N (8.9 + 2.5). Flow signal void was present, but small matrix size decreased image quality. The results of our study suggest that T2*-PSIF and T2-Turbo have good S/N and SD/N and fair image quality which may be clinically useful for breath-hold T2-weighted sequences of the liver.

Adult↗

PubMed1992

[MR tomographic studies of the cerebral circulation: the methodological principles and initial clinical experiences with T2*-weighted gradient-echo sequences and CM administration as a bolus].

Paramagnetic contrast agents produce local magnetic field inhomogeneity when they pass through the cerebrovascular system. This effect can be monitored with T2*-weighted gradient echo images, which show transient signal loss, while a bolus of GdDTPA is passing through the brain tissue. This signal loss is correlated to the local cerebral tissue perfusion and the local cerebral blood volume. In a prospective study 10 volunteers and 14 patients with cerebral infarcts and brain tumours were examined. After bolus application of GdDTPA a dynamic series of rapid T2*-weighted gradient echo images were recorded, and the local dynamics of contrast flow in brain tissue was examined. From the series of images, local changes in signal intensity were calculated pixel by pixel and presented as parameter images. By this method, infarcted areas and brain tumours can be distinguished from normal tissue by their contrast flow dynamics. The abnormal contrast dynamics depend on changes in local tissue perfusion and alterations in local blood volume. The separation of the influence of both parameters however is still an unsolved problem.

Adolescent↗

PubMed1992

Multisection FLASH: method for breath-hold MR imaging of the entire liver.

One hundred ten patients with various focal liver lesions were imaged with a multisection fast low-angle shot (FLASH) gradient-echo sequence with an echo time of 4.6 msec. This sequence enabled the acquisition of 19 T1-weighted magnetic resonance (MR) images of the liver within a single 26-second breath hold. Patients were also examined with standard T1- and T2-weighted spin-echo (SE) sequences. The multisection FLASH sequence provided significantly higher (P less than .01) liver-spleen contrast, liver-spleen signal-difference-to-noise ratio (SD/N), liver-tumor contrast, and liver-tumor SD/N than the T1-weighted SE sequence but lower values than the T2-weighted SE sequence. Motion artifacts were reduced with the multisection FLASH sequence compared with both SE sequences (P less than .01). The overall image quality of the multisection FLASH images was similar to that of the T1-weighted SE images and superior to that of T2-weighted SE images. The most important characteristics of the multisection FLASH technique in MR imaging of the liver are the high T1 contrast, the prevention of motion artifacts, and a dramatic reduction in imaging time.

Adult↗

PubMed1991

[More rapid MRT with T2-weighted spin-echo sequences through variation of the flip angle].

In the present study the influence of the flip angle on image contrast in spin echo imaging was investigated. It was evaluated, whether variation of the flip angle allows for shorter repetition and imaging times in T2-weighted spin echo sequences. 10 patients with cerebral white matter lesions were investigated with an 1.5 Tesla whole body tomograph using a conventional double-spin echo sequence (TR = 2500 ms, TE = 15 and 70 ms) and time-optimized double-spin echo sequences (TR = 1900 ms, TE 15 and 70 ms) at flip angles of 90, 80, 70, 60 and 50 degrees. A reduction of the flip angles resulted in a decrease of T1-weighting and a relative increase of T2-weighting of the images. Despite the reduced repetition time at a flip angle of 70 degrees visually and quantitatively assessed contrast between lesions and brain as well as image artifacts of the time-optimized sequence were comparable to the conventional spin echo sequence; however, imaging time was shortened about 25%.

Adult↗

PubMed1991

T1-weighted sequences for MR imaging of the liver: comparison of three techniques for single-breath, whole-volume acquisition at 1.0 and 1.5 T.

The authors compared three T1-weighted magnetic resonance imaging techniques that acquire images encompassing the entire liver in one breath hold. Twenty healthy volunteers were imaged--10 at 1.0 T and 10 at 1.5 T--and the results compared with those of regular short repetition time/echo time spin-echo imaging. Rapid acquisition spin echo was resistant to artifacts and had good image quality but had the lowest liver signal-to-noise (S/N) and spleen-liver signal-difference-to-noise (SD/N) values. Fast low-angle shot (FLASH) had the highest S/N and SD/N, very good image quality, and only mild artifacts. TurboFLASH had good S/N and SD/N, but reduced matrix size decreased image quality. All three sequences had better SD/N than regular spin echo, and FLASH and TurboFLASH had higher S/N. On the basis of this study, the FLASH sequence appears the most attractive for T1-weighted breath-hold imaging.

Adult↗

PubMed1990

Fast and precise T1 imaging using a TOMROP sequence.

Proton spin-lattice (T1) relaxation time images were computed from a data set of 32 gradient-echo images acquired with a fast TOMROP (T One by Multiple Read Out Pulses) sequence using a standard whole-body MR imager operating at 64 MHz. The data acquisition and analysis method which permits accurate pixel-by-pixel estimation of T1 relaxation times is described. As an example, the T1 parameter image of a human brain is shown demonstrating an excellent image quality. For white and gray brain matter, the measured longitudinal relaxation processes are adequately described by a single-component least-squares fit, while more than one proton component has to be considered for fatty tissue. A quantitative analysis yielded T1 values of 547 +/- 36 msec and 944 +/- 73 msec for white and gray matter, respectively.

Brain↗

PubMed1990

[A new multislice measurement sequence for the complete dynamic MR examination of the larger organs: application to the breast].

Our experience indicates that the most accurate information concerning abnormalities in the breast is obtained by a dynamic technique, in which the signal intensity before and after contrast medium injection is compared. Up to the present, only a small number of sections (1 to 5) could be obtained by dynamic MR, so that only 30-50% of the breast, depending on its size, could be examined. The availability of gradient systems, with rapid switching and high gradient amplitude and duty cycle, makes it possible to obtain a larger number of sections. A new multi-section gradient echo sequence is described, which enables one to examine the entire breast using a dynamic technique (136 images of both breasts in 14.4 minutes). Subsequent automatic post-processing, using a graphic programme, results in quantitative evaluation of the contrast images. This new sequence can be applied to dynamic MR investigations of all large organs.

Breast↗

PubMed1989

MRI of "diffusion" in the human brain: new results using a modified CE-FAST sequence.

"Diffusion-weighted"MRI in the normal human brain and in a patient with a cerebral metastasis is demonstrated. The method employed was a modified CE-FAST sequence with imaging times of only 6-10 s using a conventional 1.5-T whole-body MRI system (Siemens Magnetom). As with previous phantom and animal studies, the use of strong gradients together with macroscopic motions in vivo causes unavoidable artifacts in diffusion-weighted images of the human brain. While these artifacts are shown to be considerably reduced by averaging of 8-16 images, the resulting diffusion contrast is compromised by unknown signal losses due to motion.

Aged↗