Acoustic radiation contrast in MR images for breast cancer diagnostics--initial phantom study

Acoustic radiation contrast in magnetic resonance images is an approach to visualize the changes in ultrasonic loss and viscoelastic changes of the sample with the resolution of a magnetic resonance imaging (MRI) system. By irradiating ultrasound (US) into a tissue-mimicking sample, a displacement along the US beam path caused by the acoustic radiation force is obtained. This displacement varies with the US intensity, the duration of irradiation, the US attenuation and the viscoelastic properties of the sample. US pulses of 2.5 MHz with a duration of 20 ms and an intensity of <17 W/cm(2) are used. An MRI sequence was programmed to produce images in which the magnitude of the displacement is visualized by gray value changes. In addition, a finite element simulation of the measurements was performed to demonstrate the feasibility of the method. Through examination of the measurements and the simulations, information about viscoelastic changes was achieved. In this work, measurements on different breast phantoms are presented.

[Prospective feasibility study of chest X-ray vs. thoracic MRI in breath-hold technique at an open low-field scanner]

PURPOSE

MR investigations using a breath-hold sequence at an open low-field MR had to be compared to chest X-rays in patients with a wide spectrum of cardio-thoracic pathologies.

MATERIAL AND METHODS

114 patients and three volunteers who actually received a chest X-ray due to different indications underwent triplanar breath-hold (17 - 20 s) True-FISP sequence using a 0.2 T low-field MR (Siemens Magnetom Open, TR/TE/alpha: 7.3/3.5/80 degrees, SD: 10 mm, Pixel: 2.81 x 1.41 mm) a mean of 5.1 (+/- 8.2) days later.

RESULTS

Signal-to-noise ratio as basics for pattern recognition was 3.2 in nodule, 5.0 in infiltration, and 12.0 in effusion, and therefore True-FISP is usable for the detection of these findings. MRI demonstrated nodules (89 % vs. 57 %), infiltration (81 % vs. 71 %), pleural effusions (86 % vs. 75 %), pericardial effusions (100 % vs. 21 %) and pulmonary congestion (90 % vs. 80 %) clearly more frequently compared to chest X-ray.

DISCUSSION

MRI of the lung has been implemented successfully at an open low-field MR system. Diagnostic safety and accuracy are at least comparable to those of chest X-ray. The lack of superimposition led to a major improvement in the detection of pericardial effusions and nodules, and an increase in identification of infiltration, pleural effusion, and pulmonary congestion.

[Differentiation of benign osteoporotic and neoplastic vertebral compression fractures with a diffusion-weighted, steady-state free precession sequence]

PURPOSE

To evaluate the diagnostic accuracy of a diffusion-weighted, steady-state free precession (SSFP) sequence for the differentiation of acute benign osteoporotic and neoplastic vertebral compression fractures.

METHODS

85 patients with 102 vertebral compression fractures were examined with MR imaging using a spine array surface coil (Siemens, Vision, 1.5 Tesla). The following sequences were performed in sagittal orientation: T1-weighted spin echo (SE), short-tau inversion recovery (STIR) and a diffusion-weighted SSFP sequence (TR = 25 msec, diffusion pulse length delta = 3 msec). The SSFP images were evaluated qualitatively on a 5-grade scale from strongly hypointense to strongly hyperintense. Quantitative analysis was performed with region of interest measurements (ROI) and calculation of a bone marrow ratio.

RESULTS

60 fractures were due to osteoporosis and 42 fractures were caused by malignancy. "Hyperintensity" in a vertebral fracture on a SSFP sequence provided a sensitivity of 100 % and a specificity of 93 %. The positive predictive value was 91 %, the negative predictive value was 100 %. Quantitative analysis of the bone marrow ratio showed a statistically significant difference between the osteoporosis and the tumor group (p < 0.001). The mean value for the osteoporotic fractures was - 0.32 (SD 0.33) and + 2.07 (SD 1.37) for the tumor group.

CONCLUSION

The SSFP sequence provides a high accuracy in the differentiation of benign osteoporotic and neoplastic vertebral compression fractures.

A fast magnetic resonance imaging technique for children with mediastinal lymphoma: work in progress

BACKGROUND

Mediastinal lymphoma often presents as a large tumor at the time of diagnosis. Usually chest X-ray filming is the first imaging modality and it is used for routine follow-up during the course of the disease. A new and very fast MRI technique has been developed at our center as an alternative. Results in three patients with mediastinal lymphoma during a pilot study are promising.

PROCEDURE

After diagnosis the above patients were additionally investigated in a 0.2 T low-field MR-scanner by a modified true FISP sequence (see text) with an acquisition time of 3.6-4.6 sec. Follow-up was performed by both, X-ray filming and MRI. After diagnosis the patients, again, had both X-ray filming and MRI investigation for follow-up: one patient 2, one patient 3, and one patient 5 times. Images were evaluated and compared by two pediatric radiologists.

RESULTS

Total investigation times for radiography and MRI were comparable. The tumor was better visualized by MRI on seven of nine images and gave additional information about the structure and the localization of the tumor as well as concomitant problems such as pericardial effusion.

CONCLUSIONS

True FISP MRI may prove to be a good alternative to X-ray filming in the diagnosis and follow-up of mediastinal lymphoma.

Detection of BOLD changes by means of a frequency-sensitive trueFISP technique: preliminary results

A new method is introduced to detect magnetic field modulation arising from brain activation-induced BOLD effects. This approach uses a two-dimensional high-bandwidth, high-resolution conventional gradient-echo steady-state imaging sequence known as TrueFISP. The ability to visualize changes in oxygen saturation comes from the fact that the method is sensitive to the local field. As is well known, as the oxygen saturation changes so does the local field associated with the venous blood. We demonstrate that it is possible to visualize not only venous blood with this approach on a macroscopic level for major veins, but also to measure conventional oscillatory like signal changes during activated and resting states. Unfortunately, the method has two major drawbacks. First, a long TR is needed to maximize signal changes and, second, the field must be very well shimmed or numerous experiments need to be run to find the activation, as the signal response is sensitive to the starting frequency in the resting state. Nevertheless, these images can be compared directly with anatomical images collected with the same method without the need for distortion correction.

Combination of signal intensity measurements of lesions in the peripheral zone of prostate with MRI and serum PSA level for differentiating benign disease from prostate cancer

The aim of this study was to predict the benign or malignant nature of a prostatic lesion by defining a threshold value of signal intensity ratio and a limiting value of serum prostate-specific antigen (PSA) in patients with elevated PSA level. Twenty-six patients with elevated PSA level and no hypoechogenic lesions at endosonography underwent MR imaging using an endorectal body phased-array coil at 1.5 T (Siemens Magnetom Symphony). A T2-weighted turbo-spin-echo (TSE) pulse sequence was applied in a transverse orientation. Two radiologists evaluated the images. In the presence of a pathological finding they defined regions of interest (ROI) in the suspicious pathological area of the peripheral zone and in muscle for reference. The quotient of the two ROIs was calculated and then correlated with the actual PSA level. Diagnosis was confirmed by prostate biopsy. Ten of 12 patients with quotients smaller than 4 showed cancer at histology. Nine of 12 men with cancer proven by biopsy had PSA levels higher than 10 ng/ml. A significant difference (p < 0.001) was found between the quotients of cancer and quotients of chronic prostatitis, fibrosis, or glandular atrophy. The accuracy of tumor differentiation of the method was 77%. Measurement of signal intensity quotients in the peripheral zone of the prostate in combination with knowledge of defined limits of PSA levels the technique could be helpful in detecting additional cancer areas for prostate biopsy. False-negative tumor results of standard sextant biopsy can be reduced. In men with high PSA values the method has a role in differentiating between patients who require prostate biopsy and those of clinical observation.

Low field thoracic MRI--a fast and radiation free routine imaging modality in children

Radiography of the chest is the most frequently performed radiological examination in pediatric imaging. However, it is associated with the application of ionizing radiation. In order to avoid ionizing radiation in children a new and very fast MRI technique has been developed at our center as an alternative to the pediatric chest X-ray. 100 patients who had received a chest X-ray were additionally investigated in a 0.2 T low-field MR-scanner by a modified true FISP sequence with an acquisition time of 3.6-4.6 s for a coronal triple-slice scan. X-ray and MR images were independently evaluated and later compared by two pediatric radiologists. Total investigation times (door-to-door time) for X-ray and MRI were comparable. The signal-to-noise ratio for lung parenchyma was 4.6-7.3. Of 189 pathologic findings 165 were depicted on MR images as well as radiographs, 18 were noted on MRIs only, 6 on X-rays only. Overall kappa was 0.87. True FISP MRI may be a good alternative to conventional chest X-ray. The main advantages are: fast imaging free of ionizing radiation, easy performance, no need for special equipment, optional imaging in all 3 planes, good image quality, and a high diagnostic value.

MR lung imaging at 0.2 T with T1-weighted true FISP: native and oxygen-enhanced

An inversion recovery true fast imaging with steady precession (FISP) pulse sequence was developed to carry out fast imaging of the lungs at 0.2 T. Using this sequence, oxygen-enhanced magnetic resonance (MR) lung imaging was performed on healthy volunteers. The lungs showed signal enhancement (11.7% +/- 3.8%) when breathing 100% oxygen. Using inversion recovery, true FISP at low field may prove promising for MR lung imaging.

Diffusion-weighted imaging of tumor recurrencies and posttherapeutical soft-tissue changes in humans

The aim of this study was to examine soft tissue tumor recurrences and posttherapeutic soft tissue changes in humans with a diffusion-weighted steady-state free precession (SSFP) sequence. Twenty-four patients with 29 pathologies of the pelvis or the extremities were examined. The lesions were classified as follows: group 1, recurrent viable tumors (n = 10); group 2, postoperative hygromas (n = 7); and group 3, posttherapeutic reactive inflammatory muscle changes (n = 12). The sequence protocol in these patients consisted of short tau inversion recovery images, T2-weighted spin-echo (SE), pre- and postcontrast T1-weighted SE images and the diffusion-weighted SSFP sequence. The signal loss on diffusion-weighting was evaluated visually on a four-grade scale and quantitatively. The signal intensities were measured in regions of interest and a regression analysis was performed. Statistical analyses was performed utilizing the Student's t-test. The signal loss was significantly higher for hygromas and edematous muscle changes than for recurrent tumors (p < 0.001) indicating higher diffusion of water protons. The regression coefficient was -0.11 (mean) for tumors. Hygromas had a significantly higher signal loss than inflammatory edematous muscle changes (p < 0.01). The regression coefficients were -0.29 (mean) for hygromas and -0.22 (mean) for edematous muscle changes. The SSFP sequence seems to be a suitable method for diffusion-weighted imaging of the musculoskeletal system in humans. These preliminary results suggest that the signal loss and the regression coefficients can be used to characterize different types of tissue.

Diagnostic value of increased diffusion weighting of a steady-state free precession sequence for differentiating acute benign osteoporotic fractures from pathologic vertebral compression fractures

BACKGROUND AND PURPOSE

Differentiating acute benign from neoplastic vertebral compression fractures can pose a problem in differential diagnosis on routine MR sequences, as signal changes can be quite similar. Our purpose was to assess the value of increasing the diffusion weighting of a diffusion-weighted steady-state free precession (SSFP) sequence for differentiating these two types of vertebral compression fractures.

METHODS

Twenty-nine patients with 32 acute vertebral compression fractures caused by osteoporosis (n = 15) or malignancy (n = 17) were examined with a diffusion-weighted SSFP sequence, a T1-weighted spin-echo sequence, and a short-inversion-time inversion recovery sequence. The SSFP sequence was performed with increased diffusion weighting (delta = 0.6, 3.0, 6.0, and 9.0 ms). The signal intensities of the fractured vertebral bodies were rated on a five-point scale from markedly hypointense to markedly hyperintense relative to normal adjacent vertebral bodies. Quantitative analysis was performed by region-of-interest measurements and by calculating the bone marrow contrast ratio. Statistical analysis was performed with the Mann Whitney U test and Student's t test.

RESULTS

At delta = 3 ms, the osteoporotic fractures yielded hypointense signal in seven cases, isointense signal in six, and hyperintense signal in two. The fractures showed a progressive signal loss with increased diffusion weighting, so that hypointensity was reached in all but one case. All metastatic fractures had hyperintense signal with delta = 3 and 6.0 ms. With delta = 9.0 ms, four fractures became isointense.

CONCLUSION

Increasing diffusion weighting can reduce false-positive hyperintense osteoporotic fractures or make hypointensity more obvious in cases of osteoporotic fractures.

[HIRE (high intensity reduction). New cerebrospinal fluid suppressed T2-weighted imaging sequence]

PURPOSE

The HIRE sequence utilizes the very long T2 value of CSF to suppress its high signal contribution in T2-weighted imaging by an image subtraction technique.

METHODS

To assess the diagnostic potential of a new dark fluid sequence HIRE (High Intensity REduction) in the diagnostic work-up, 20 patients with histologically confirmed cerebral gliomas were examined with T2-weighted FSE, T1-weighted SE, fast FLAIR and HIRE using identical scan parameters. In patients with enhancing lesions fast FLAIR and HIRE were added to the contrast-enhanced T1-weighted SE images. Images were analyzed in a qualitative and quantitative evaluation. In the qualitative lesion analysis, lesion delineation and differentiation between enhancing and non enhancing tumor tissue were by two readers. For the quantitative analysis lesion-to-background and lesion-to-CSF contrast and contrast to noise ratios were determined in an region of interest analysis.

RESULTS

HIRE achieved a significant reduction of the CSF signal without loosing the high gray-to-white matter contrast of T2 weighted sequences. In the quantitative analysis, the contrast ratios of the HIRE were lower compared to the FLAIR images due to a relative high background and CSF signal. After the application of contrast media HIRE images revealed a significant signal increase in enhancing lesions, which subsequently increased the contrast and contrast-to-noise ratios. In the qualitative analysis, both readers found all tumors clearly delineated on HIRE imaging. Compared to T2-weighted FSE the tumor delineation with HIRE was better in nine patients, equal in four patients and less in one patient. Compared to the FLAIR images HIRE was rated superior in three patients, equal in nine patients and inferior in another three patients. Delineation of the enhancing tumor parts was possible with HIRE in all patients. HIRE images present significant less image artifacts than FLAIR images due to reduced inflow effects.

CONCLUSIONS

The presented T2 based HIRE sequence is an alternative to the T1 based FLAIR sequence with the advantage of a better gray to white matter contrast and shorter measurement time. Due to the subtraction technique signal intensities from tissues with T2 relaxation times in the range between white matter and CSF are also partially affected depending on their T2 values. With respect to this undesired effect, an improvement in HIRE imaging will be expected by a self-weighted subtraction algorithm.

Optimization and evaluation of the signal intensity change in multisection oxygen-enhanced MR lung imaging

The behavior of the signal intensity in MRI of human lungs was investigated during inhalation of pure oxygen. Nine volunteers were examined, five using a breath-hold and four using a non-breath-hold technique. Four coronal slices were acquired in each volunteer using an inversion recovery turbo spin-echo sequence. The inversion time of the sequence was optimized for maximum contrast. Breathing of pure oxygen and room air was alternated in the volunteers. Breath-hold and non-breath-hold cases were compared. Breathing pure oxygen lead to a statistically significant signal intensity increase (up to 18%) compared to breathing room air. In addition, T(1) maps were acquired during breathing 100% oxygen and room air. Inhalation of pure oxygen reduced the mean T(1) time of the lungs from 1280 (+/-85) msec to 1224 (+/-139) msec without breath-hold and from 1219 (+/-176) to 1074 (+/-92) msec with breath-hold. Therefore, an optimized sequence and measurement protocol provided significant signal intensity changes utilizing 100% oxygen. Magn Reson Med 43:860-866, 2000.

Assessment of cerebral gliomas by a new dark fluid sequence, high intensity REduction (HIRE): a preliminary study

The purpose of this study was to assess the diagnostic potential of a new dark fluid sequence, high intensity reduction (HIRE) in the diagnostic workup of patients with cerebral gliomas. The HIRE sequence utilizes a very long T(2) value of the cerebrospinal fluid (CSF) to suppress its high signal contribution in T(2)-weighted imaging by a image subtraction technique. Fifteen patients with histologically confirmed cerebral gliomas were examined with T(2)-weighted fast spin-echo (FSE), T(1)-weighted SE, fast fluid-attenuated inversion recovery (FLAIR), and HIRE imaging using identical scan parameters. In patients with enhancing lesions, fast FLAIR and HIRE were added to the contrast-enhanced T(1)-weighted SE images. Images were analyzed in a qualitative and quantitative evaluation. In the qualitative analysis, lesion detection, lesion delineation, and differentiation between enhancing and non-enhancing tumor tissue were assessed in a two-reader study. For the quantitative analysis, lesion-to-background and lesion-to-CSF contrast and contrast-to-noise ratios were determined in a region of interest analysis. HIRE achieved a significant reduction of the CSF signal without losing the high gray-to-white matter contrast of T(2)-weighted sequences. In the quantitative analysis, the contrast ratios of the HIRE images were lower compared with the FLAIR images due to a relatively high background and CSF signal. After administration of contrast media, HIRE images presented a significant signal increase in enhancing lesions, which subsequently increased the contrast and contrast-to-noise ratios. In the qualitative analysis, both readers found all tumors clearly delineated on HIRE imaging. Compared with T(2)-weighted FSE, the tumor delineation with HIRE was better in nine patients, equal in four patients, and less in one patient. Compared with the FLAIR images, HIRE was rated superior in three patients, equal in nine patients, and inferior in another three patients. Delineation of the enhancing tumor parts was possible with HIRE in all patients. HIRE images had significantly fewer image artifacts than FLAIR images due to reduced inflow effects. The T(2)-based HIRE sequence presented is an alternative to the T(1)-based FLAIR sequence, with the advantage of better gray-to-white matter contrast and shorter measurement time. Due to the subtraction technique, signal intensities from tissues with relaxation times in the range T(2 WM) < < T(2) < T(2 CSF) are also gradually affected, corresponding to their T(2) values. With respect to this unwanted effect, an improvement in HIRE imaging will be possible by using a self-weighted subtraction algorithm. In a forthcoming study this concept will first be tested on appropriate phantom fluids.

Diffusion-weighted MR imaging of bone marrow: differentiation of benign versus pathologic compression fractures

PURPOSE

To evaluate the usefulness of diffusion-weighted magnetic resonance (MR) imaging of bone marrow for differentiating between benign and pathologic vertebral compression fractures.

MATERIALS AND METHODS

Thirty patients with 39 vertebral compression fractures were examined with MR imaging. Diffusion-weighted MR imaging was performed with a steady-state free precession sequence in 22 acute benign osteoporotic and/or traumatic fractures and 17 pathologic compression fractures. Biplanar radiographs, T1-weighted spin-echo (SE) MR images, and short inversion time inversion-recovery (STIR) MR images were available for all patients. The signal intensity characteristics were analyzed qualitatively and quantitatively (bone marrow contrast ratios and signal-to-noise ratios) for all sequences.

RESULTS

At diffusion-weighted MR imaging, all benign vertebral compression fractures were hypo- to isointense to adjacent normal vertebral bodies. Pathologic compression fractures were hyperintense to normal vertebral bodies. Benign vertebral fractures had negative bone marrow contrast ratios at diffusion-weighted imaging, whereas pathologic vertebral fractures had positive values (P < .001). The difference in bone marrow contrast ratios for benign and pathologic compression fractures at T1-weighted SE and STIR imaging was not significant (P > .01).

CONCLUSION

Diffusion-weighted MR imaging provided excellent distinction between pathologic and benign vertebral compression fractures.

Diffusion-weighted MRI in transient global amnesia: elevated signal intensity in the left mesial temporal lobe in 7 of 10 patients

Prompted by the findings of previous studies with positron emission tomography and single photon emission computed tomography, which demonstrated hypoperfusion or hyperperfusion in the left temporal lobe in isolated patients with transient global amnesia (TGA), we compared the sensitivity of diffusion-weighted (DW) magnetic resonance imaging (MRI) with that of conventional T1- and T2-weighted MRI in patients with TGA. Ten patients with the typical syndrome of a pure TGA were included in the study. For all patients, a coronal DW sequence, a steady-state free precession (SSFP) sequence, and conventional T1- and T2-weighted turbo spin-echo sequences were obtained. Seven of the 10 patients had elevated signal intensity in the left hippocampal region on DW MRI; moreover, 3 of these 7 patients exhibited bilateral signal abnormality in this sequence. All conventional T1- and T2-weighted images as well as all follow-up studies were normal. The signal elevation in DW MRI correlates with a decrease in the interstitial space and with cellular edema in the temporal lobe during TGA. The underlying pathomechanism causing this cellular edema cannot be clearly outlined using DW MRI. Our data are, however, compatible with spreading depression. This is the first study to show that DW MRI is a sensitive MRI method for evaluating TGA, especially in the early stage of the disease.

MR cisternography: a new method for the diagnosis of CSF fistulae

The aim of this study was to compare a new MRI method for detecting the existence of cerebrospinal fluid (CSF) fistulae, i. e. MR cisternography, with CT cisternography. In a prospective study, 30 patients with post-traumatic CSF fistulae were examined. The MR examinations were performed with a 1.0-T whole-body MR system, using two T2(*)-weighted sequences, a 3D PSIF (time-inversed fast imaging with steady-state precession, FISP) and a 3D constructive interference steady-state (CISS) sequence. The results of MRI and CT cisternography were compared with the surgical findings. The sensitivity in detecting CSF fistulae with MR cisternography (PSIF: 89.9 %; CISS: 93.6 %) was higher than with CT cisternography (72.3 %). The sensitivity of CT cisternography at detecting CSF fistulae in patients with a size of dural lesion less than 2 mm or in patients with multiple dural lesions is significantly lower compared with the MR method. Although the localization of CSF fistulae always proved possible with MR cisternography, this could only be accomplished wih CT in 70 % of cases. The MR cisternography technique is a new examination method with a higher sensitivity for the detection of CSF fistulae than CT cisternography. The CISS technique is superior compared with PSIF and should be used in patients with high-flow CSF fistulas.

[MR diagnosis of cerebrospinal fluid fistulas using a 3D-CISS sequence]

PURPOSE

We compared a new MR method for diagnosis of CSF fistulas with CT cisternography.

MATERIAL AND METHODS

In a prospective case study we examined 35 patients with posttraumatic CSF fistulas and compared the results with the intraoperative findings. The MR investigation was performed using a 1.0T whole body MR-system. We used a strongly T2*-weighted 3D-CISS sequence. The examinations were performed in prone position, in patients with severe CSF rhinorrhoea additionally in supine position.

RESULTS

The sensitivity and specificity of the MR method (88.9% and 95.1%) is higher compared with CT cisternography (77.8% and 87.8%). The reason for the lower sensitivity of CT compared with MRI are complex fracture systems, involving several paranasal cavities in patients with false positive results in CT cisternography. Reasons for the lower specificity of CT cisternography are false negative results in patients with small dural lesions below 2 mm2.

CONCLUSION

Using a new method MRI can detect CSF-fistulas. The MR method is superior to CT cisternography, is noninvasive, the administration of contrast and agent is no longer necessary.

Comparison of transcranial sonography, magnetic resonance imaging, and single photon emission computed tomography findings in idiopathic spasmodic torticollis

Various lines of evidence suggest that the basal ganglia and thalamus are involved in the pathogenesis of idiopathic dystonia, but unfortunately neuroradiological and pathological data are sparse and controversial. In this study, we have examined 10 patients with spasmodic torticollis by neuroimaging techniques, including transcranial sonography (TS; n = 10), conventional (n = 10) and diffusion-weighted (n = 5) magnetic resonance imaging (MRI), and single photon emission computed tomography (SPECT; n = 10), employing [123I]iodobenzamide (IBZM) as a ligand with a high affinity to the D2 receptor. In seven patients, TS showed small hyperechogenic lesions in the medial segments of the lentiform nucleus contralateral to the side of head deviation. In accordance with the site of TS abnormalities, diffusion-weighted MRI displayed a hyperintense lesion in only one patient, while standard MRI of this area was normal in all patients. SPECT revealed a slight but statistically nonsignificant reduction of IBZM tracer uptake in an area corresponding to the dorsal portions of the striatum in 9 of the 10 patients. TS findings support the hypothesis that structural alternations of the pallidothalamic circuit contralateral to the side of head deviation are involved in the pathogenesis of idiopathic spasmodic torticollis. TS may be more sensitive in detecting basal ganglia alterations than MRI.

Diffusion measurements in the ischemic human brain with a steady-state sequence

RATIONALE AND OBJECTIVES

The authors evaluate the clinical usefulness of a diffusion-weighted steady-state free-precession (SSFP) sequence to detect acute and subacute ischemic changes.

METHODS

Twenty-four patients were examined on a 1.5-tesla scanner, using a SSFP-sequence (repetition time [TR]/ echo time [TE] = 22/3-8 mseconds). The slice thickness was 5 mm, 10 averages, 57 seconds per slice. The diffusion gradient strength was 23 millitesla/m, with b-values from 165 to 598 seconds/mm2. Diffusion-weighted images (DWI) were compared with T2-weighted images.

RESULTS

The diffusion-weighted SSFP sequence produced diagnostic quality images in 23 of 24 patients. Diffusion depicted (group 1: 0-12 hours) more acute lesions (3 of 6) than T2-weighted images (2 of 6); the mean lesion diameter depicted by diffusion was 10.9 mm (standard deviation [SD], 12.3) and in T2-weighted images was 4.7 mm (SD 6.8). A significant correlation (P < 0.017) in subacute lesions was found when diffusion was compared with turbo spin echo (mean size difference/T2 = 18.5/17.5 mm, SD 13.2/12.2).

CONCLUSIONS

The diffusion-weighted SSFP-sequence is more sensitive in acute ischemia and delineates likewise in subacute ischemia, when compared with T2-weighted imaging.

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.

Misleading changes of the signal intensity on opposed-phase MRI after injection of contrast medium

OBJECTIVE

The effect of opposed-phase imaging on the interpretation of MR contrast studies is highlighted.

MATERIALS AND METHODS

A model calculation is performed. It demonstrates the change of signal intensity of an average tumor before and after application of Gd-DTPA on an in-phase and an opposed-phase image, depending on the percentage of fat within the voxels. The effect is then demonstrated, using a small cotton stick soaked with water or a solution of contrast agent representing a tumor before and after i.v. application of Gd-DTPA.

RESULTS

If an average enhancing tumor, which is surrounded by fat, occupies less than 50-60% of the slice thickness, it becomes undetectable on opposed-phase images. The reason is that due to signal cancellation on the opposed image, no signal change or even signal decrease results, while signal increase is visible on the in-phase image.

CONCLUSION

In those areas of the body where significant partial volume of a tumor with fat may occur (such as for breast tumors growing along ducts, which are surrounded by fat), severe errors can result. Therefore we explicitly warn from using opposed-image sequences for MR contrast studies.

Dynamic snapshot gradient-echo imaging of head and neck malignancies: time dependency and quality of contrast-to-noise ratio

The purpose of this study was to evaluate the time dependency of the contrast-to-noise ratio (CNR) of head and neck malignancies during contrast-enhanced MR imaging. Then we would compare the CNR of dynamic snapshot gradient-echo (SGE) images with conventional spin-echo (SE) and fast spin-echo (FSE) sequences. Fifteen patients with squamous cell carcinomas were examined with T1W-SE, T2W-FSE, contrast-enhanced Gd-T1W-SE, and T1W-SGE sequences, the latter statically and contrast-enhanced dynamically. The CNR for all sequences and adjacent tissues was computed and the time to reach maximal CNR (Tmax) was determined for dynamic studies. The CNR was time dependent with two distinct Tmax at 6-18 and 60-160 s which corresponded to two different tumor enhancement patterns. Neither enhancement pattern correlated with distinct histologic findings or tumor grading. The CNR improved for the Gd-T1W-SE images. The improvement was statistically significant in relation to T1W-SE and Gd-T1W-SE images at the floor of the mouth and at the tongue base. The good CNR of the dynamic Gd-T1W-SGE measurements justifies further investigations of this method in order to improve tumor delineation.

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.

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.

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.

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.

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.

Assessment of cerebral blood volume with dynamic susceptibility contrast enhanced gradient-echo imaging

OBJECTIVE

Dynamic susceptibility contrast (DSC) enhanced MRI was used to study relative cerebral blood volume (rCBV).

MATERIALS AND METHODS

We examined 15 healthy subjects and 47 patients with vascular stenosis or occlusion, with brain infarctions, and with cerebral neoplasms. During bolus injection of Gd-diethylenetriamine pentaacetic acid, a series of rapid T2*-weighted fast low angle shot two-dimensional images were recorded from the same slice. From these images, changes in signal intensity during bolus passage were computed pixel-by-pixel and converted into contrast agent concentration curves. Applying the principles of indicator dilution theory, images of rCBV were calculated.

RESULTS AND CONCLUSION

Regions of infarctions show almost zero rCBV. In patients with high-grade vascular stenosis or occlusion a bolus delay in comparison to the unaffected side and an increased mean transit time can be observed. Some of the affected areas show an increased rCBV, which is a well-known physiological mechanism that takes place to compensate for the reduced cerebral blood pressure. In brain tumors, rCBV imaging reveals focal or homogeneous areas of increased blood volume. This can even be observed in low-grade astrocytomas with unaffected blood-brain barrier. In CBV imaging, the effects of radiotherapy on tumor tissue can be monitored as a significant decrease of rCBV in tumor tissue after therapy.

[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.

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.

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.

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.

Constructive interference in steady state-3DFT MR imaging of the inner ear and cerebellopontine angle

PURPOSE

To assess the value of a three-dimensional Fourier transformation MR technique "CISS" (constructive interference in steady state) in imaging the inner ear.

SUBJECTS

We studied 50 normal inner ears (40 axial, 10 coronal) and 10 pathologic inner ears in 60 patients.

RESULTS

The cochlea, semicircular canals, and vestibulum were visualized in detail. Cranial nerve VII and the cochlear, superior vestibular, and inferior vestibular branch of cranial nerve VIII were identified in 90%, 94%, 80%, and 88% of the cases, respectively. A vascular loop was recognized inside the internal auditory canal in 6%, and in the porus in 30%, of the cases. The high signal of the cerebrospinal fluid and labyrinthine fluids (perilymph and endolymph) on the CISS images made excellent delineation of tumors in the cerebellopontine angle and internal canal possible and allowed detection of tumoral labyrinth involvement. The thin sections, high resolution of the images, and capability of producing multiplanar and three-dimensional reconstructions often offered additional information.

CONCLUSIONS

The CISS sequence allows detailed study of the normal and pathologic inner ear and promises to be highly valuable in the demonstration of the vascular loop.

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.

[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.

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.

MR imaging of the pancreas at high field strength: comparison of six sequences

The authors compared six MR sequences comprising conventional breath-hold [rapid spin echo (RASE) repetition time (TR) 240 ms/echo time (TE) 8 ms/90 degrees, fast low angle shot (FLASH) 130/4.5/80 degrees, TurboFLASH 6.5/3.5/8 degrees], fat suppressed regular spin echo (FS SE 330/15/90 degrees), and two combined fat suppressed breath-hold sequences (FS FLASH 130/8/80 degrees, FS RASE 240/10/90 degrees) for studying the normal pancreas. Sequences were selected on the basis of features desirable for demonstrating the pancreas, particularly absence or decrease in artifacts and improved dynamic range of intraabdominal tissue signal intensities. Ten normal volunteers were studied, six at 1.5 T and four at 1.0 T, and comparison was made to regular short TR/TE SE. Quantitative pancreas signal-to-noise (S/N) and pancreas fat-to-noise (SD/N) measurements and qualitative evaluation of overall resolution and artifacts were determined. Fat suppressed FLASH had the highest S/N (44.1 +/- 10.8, p less than 0.0001) and SD/N (35.0 +/- 11.9, p less than 0.0001), and seven studies were considered good or very good. Fat suppressed SE had good S/N (32.6 +/- 7.7) and SD/N (19.0 +/- 3.6), and eight FS SE studies were considered good or very good. Among the nonsuppressed sequences, FLASH had the best combination of quantitative and qualitative measurements. Our results suggest that fat suppression may be important for studying the pancreas and that nonsuppressed FLASH may be a reasonable alternative.

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.

[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%.

[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.

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.

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.

[Clinical use of gradient echo sequences of longer repetition times]

Studies designed to optimise image contrasts of gradient echo sequences showed, that especially repetition times between 250 and 500 ms in combination with adequate echo times and flip angles provide new image contrasts. The clinical purpose of gradient echo sequences with longer TR was systematically evaluated in 450 patients. A major advantage of GE sequences was the low signal intensity of fat and bone tissue. On the other hand different pathologic changes showed a high signal intensity in comparison to T2 weighted spin echo sequences as well. With the possibility of multiple slices GE sequences were of outstanding diagnostic value especially in MR of soft tissue and of the musculoskeletal system. T2 weighted SE sequences provided no additional informations and could therefore be omitted in a great number of examinations.

A new steady-state imaging sequence for simultaneous acquisition of two MR images with clearly different contrasts

We present a new steady-state imaging sequence, which simultaneously allows in a single acquisition the formation of two MR images with clearly different contrasts. The contrast of the first image is FISP-like, whereas the second image is strongly T2-weighted. In principle the T2 values in the image can be calculated from the combination of the first and second images. We also show calculated T2 images.