Biomedical subjects

Stefan Maderwald

Publications and source records attributed to Stefan Maderwald.

11 recordsLinked to original sources

PubMed2006

Time-resolved contrast-enhanced magnetic resonance angiography of the hand with parallel imaging and view sharing: initial experience.

We sought to compare a three-dimensional, contrast-enhanced, magnetic resonance angiogram (3D CE MRA) sequence combining parallel-imaging (generalised autocalibrating partially parallel acquisitions (GRAPPA)) with a time-resolved echo-shared angiographic technique (TREAT) in an intraindividual comparison to a standard 3D MRA sequence. Four healthy volunteers (27-32 years), and 11 patients (11-82 years) with vascular pathologies of the hand were examined on a 1.5-Tesla (T) MR system (Magnetom Avanto, Siemens, Erlangen, Germany) using two multichannel receiver coils. Following automatic injection (flow rate 2.5 cc/s) of 0.1 mmol/kg gadoterate (Dotarem, Guerbet, Roissy, France), 32 consecutive 3D data sets were collected with the TREAT sequence (TR/TE: 4.02/1.31 ms, FA: 10 degrees, GRAPPA acceleration factor: R=2, TREAT factor: 5, voxel size: 1.0 x 0.7 x 1.3 mm(3)) and a T1-wwighted 3D gradient-echo sequence (TR/TE: 5.3/1.57 ms, FA: 30 degrees, GRAPPA acceleration factor: 2, voxel size: 0.71 x 0.71 x 0.71 mm(3,)). MR data sets were evaluated and compared for image quality and visualisation of vascular details. In the volunteer group, all MR imaging was successful while technical problems prevented acquisition of the standard protocol in two patients. For the corresponding segments, the number of visible segments was equal on both sequences. Overall image quality was significantly better on the standard protocol than on the TREAT protocol. TREAT MRA provided functional information in lesions with rapid blood flow, e.g. detection of feeding and draining vessels in an haemangioma. TREAT-MRA is a robust technique that combines morphological and functional information of the hand vasculature and deals with the very special physiological demands of vascular lesions, such as quick arteriovenous transit time.

Adolescent↗

PubMed2006

Accelerating MR elastography: a multiecho phase-contrast gradient-echo sequence.

PURPOSE: To demonstrate the feasibility of using a multiecho phase-contrast (PC) gradient-echo sequence with motion-sensitizing gradient (MSG) to accelerate MR elastography (MRE) acquisitions in comparison to single-echo PC sequences. MATERIALS AND METHODS: The sequence was implemented and compared with a conventional single-echo sequence as the standard of reference in both agarose phantoms and in vivo in the biceps of three healthy volunteers. For reconstruction of the elasticity modulus, a local frequency estimation (LFE) algorithm was used. ETL factors of 1-16 were evaluated. RESULTS: Phantom experiments demonstrated excellent consistency between single-echo and multiecho measurements in terms of wave equivalency, SNR, and reconstructed shear modulus. Additionally, the in vivo MRE examinations showed an excellent correspondence to the single-echo results. Minor loss of wave amplitude was observed at higher ETL factors. CONCLUSION: The results demonstrate that a multiecho sequence is suitable for accelerating MRE in nearly homogeneous tissue, such as muscle. It provides equivalent elasticity values in a significantly reduced scan time compared to a single-echo sequence. The maximum achievable ETL factor must be individually determined for the target tissue.

Acceleration↗

PubMed2006

Oscillating steady states.

The signal formation and properties of steady-state free precession (SSFP) in combination with alternating RF pulse phases or alternating spin precession is analyzed. Simulations and experiments demonstrate that the amplitudes of SSFP echo paths are significantly influenced by application of alternating phases either via the exciting RF pulse or via some external mechanism producing alternating spin precession. The influence of alternating phases on echo amplitudes is different for different echo paths. The primary SSFP echo paths F(0) (-) and F(0) (+) exhibit a signal reduction whereas higher-order echoes F(-1) (-) and F(1) (+) show a signal increase upon application of oscillating phases. This behavior can be described using a simple perturbation theory applied to the frequency response profile of balanced SSFP combined with a final signal integration over one balanced SSFP band. The high sensitivity of SSFP echo amplitudes to alternating RF pulse phases or precession is exemplarily used to detect and visualize propagating transverse acoustic shear waves. Detection of flow or alternating currents are further possibilities to apply this unique feature of SSFP.

Magnetic Resonance Imaging↗

PubMed2005

Comparison of volume, four- and eight-channel head coils using standard and parallel imaging.

Array coils can potentially offer increased signal-to-noise ratio (SNR) over standard coils adjacent to the array elements, while preserving the SNR at the center of the volume. The SNR advantage should theoretically increase with the number of array elements. Parallel acquisition techniques (PAT), on the other hand, can benefit acquisition times or spatial resolution at a cost to SNR as well as image quality. This study examines the question of whether SNR and image quality are still acceptable with two different array coils (four and eight channels) in conjunction with PAT when compared to standard imaging with a volume coil. All imaging was on a 1.5 T MR scanner. T2-weighted, FLAIR, diffusion-weighted, and time of flight (TOF) angiography images were performed with and without PAT in a phantom and in ten healthy volunteers. The phantom measurements demonstrated superior SNR for the eight-channel coil versus the four-channel and standard head coils. Using the eight-channel head coil for in vivo imaging, image quality with PAT (acceleration factor=2) was scored similar to images without PAT using the volume coil. The four-channel head coil suffered from inhomogeneity, lower SNR and poorer image quality when using PAT compared to standard imaging with the volume head coil. Both the in vivo and the phantom results indicate that the eight-channel head coil should be used for the highest quality brain images; this coil can be combined with PAT sequences for shorter acquisition time without a significant decrease in image quality relative to a volume coil without PAT.

Adult↗

PubMed2005

Parallel acquisition techniques for accelerated volumetric interpolated breath-hold examination magnetic resonance imaging of the upper abdomen: assessment of image quality and lesion conspicuity.

PURPOSE: To evaluate the impact of parallel acquisition techniques (PATs) on image quality and detection of liver metastases using three-dimensional volumetric interpolated breath-hold examination (VIBE) for clinical liver imaging. MATERIALS AND METHODS: Forty-nine patients with various primary malignancies underwent abdominal dynamic contrast-enhanced three-dimensional VIBE magnetic resonance imaging (MRI) (1.5 T) using a standard phased array coil. Recently introduced Generalized Autocalibrating Partially Parallel Acquisition (GRAPPA) and SENSitivity Encoding (mSENSE) PAT reconstruction algorithms were added to reduce scan time twofold. Overall image quality, motion, and aliasing artifacts were classified on a 5-point scale. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements were performed for quantitative comparison. All sequences were evaluated concerning the number of detected lesions. RESULTS: PAT resulted in a reduction of data acquisition time from 23 to 13 seconds. Both GRAPPA and mSENSE data sets yielded 30% less SNR (34.8 +/- 14.1 and 33.1 +/- 13.3, P < 0.001) and 35% less CNR (21.2 +/- 15.0 and 20.9 +/- 12.7, P < 0.05) in comparison to unaccelerated VIBE (SNR = 50.8 +/- 20.3/CNR = 32.5 +/- 19.1). Similarly, PAT revealed lower-image-quality scores than unaccelerated VIBE. GRAPPA resulted in more fold-over artifacts than mSENSE. mSENSE revealed slightly fewer motion artifacts than no PAT. The unaccelerated late-venous-phase VIBE sequence revealed 146 lesions in the same patients. Accelerated images with mSENSE reconstruction detected 138 lesions. GRAPPA revealed 127 lesions, and thus performed inferior to mSENSE. CONCLUSION: At least for arrays with small numbers of elements, such as arrays used in this study, the PAT-induced reduction in scanning times must be weighed against compromises in image quality, which translate into poorer diagnostic performance regarding detection of small hepatic lesions. Thus, the PAT implementations tested in this study should probably be reserved for patients unable to hold their breaths for regular three-dimensional VIBE data sets.

Abdomen↗

PubMed2005

A diffusion tensor imaging analysis of gender differences in water diffusivity within human skeletal muscle.

The diffusive properties of adjacent muscles at rest were evaluated in male (n = 12) and female (n = 12) subjects using diffusion tensor imaging (DTI). The principle, second and third eigenvalues, trace of the diffusion tensor [Tr(D)], and two anisotropic parameters, ellipsoid eccentricity (e) and fractional anisotropy (FA), of various muscles in the human calf were calculated from the diffusion tensor. Seven muscles were investigated in this study from images acquired of the left calf: the soleus, lateral gastrocnemius, medial gastrocnemius, posterior tibialis, anterior tibialis, extensor digitorum longus and peroneus longus. A mathematical model was also derived that relates the eigenvalues of the diffusion tensor to the muscle fiber volume fraction, which is defined as the volume of muscle fibers within a well-defined arbitrary muscle volume. Females on average had higher eigenvalues and Tr(D) compared with males, with the majority of muscles being statistically different between the sexes. In contrast, males on average had higher e and FA than females, with the large plantar flexors--soleus, lateral gastrocnemius, and medial gastrocnemius--producing statistically different results. The behavior of the mathematical model for variations in fiber volume fraction produced similar trends to those seen when the experimental data were fit to the model. The model predicts that a larger volume fraction of skeletal muscle in males is devoted to fibers than in females, but the true underlying source of the gender discrepancy remains unclear. Although the model does not fully account for other transport processes, it does provide some insight into the limiting factors that affect the diffusion of water in skeletal muscle measured by DTI.

Adult↗

PubMed2004

Parallel acquisition techniques in cardiac cine magnetic resonance imaging using TrueFISP sequences: comparison of image quality and artifacts.

PURPOSE: To compare image quality, artifacts, and signal-to-noise ratio (SNR) in cardiac cine TrueFISP magnetic resonance imaging (MRI) with and without parallel acquisition techniques (PAT). MATERIALS AND METHODS: MRI was performed in 16 subjects with a TrueFISP sequence (1.5 T; Magnetom Sonata, Siemens): TR, 3.0 msec; TE, 1.5 msec; flip angle (FA), 60 degrees. Three axes were scanned without PAT (no PAT) and using the generalized autocalibrating partially parallel acquisition (GRAPPA) and modified sensitivity encoding (mSENSE) reconstruction algorithms with an autocalibration mode to reduce scan time. A conventional spine array and a body flex array were used. Artifacts, image noise, and overall image quality were classified on a 4-point scale by an observer blinded to the implemented technique; for quantitative comparison, SNR was measured. RESULTS: With a PAT factor of two, acquisition time could be reduced by 39%. No PAT did not show artifacts, and GRAPPA revealed fewer artifacts than mSENSE. PAT provided inferior-quality scores concerning image noise and overall image quality. In quantitative measurements, GRAPPA and mSENSE (20.1 +/- 6.2 and 15.6 +/- 6.2, respectively) yielded lower SNR than no PAT (30.6 +/- 20.1; P < 0.05) and P < 0.001). CONCLUSION: Time savings in PAT are accompanied by artifacts and an increase in image noise. The GRAPPA algorithm was superior to mSENSE concerning image quality, noise, and SNR.

Adult↗

PubMed2004

In vivo elasticity measurements of extremity skeletal muscle with MR elastography.

MR elastography (MRE) has been shown to be capable of non-invasively measuring tissue elasticity even in deep-lying regions. Although limited studies have already been published examining in vivo muscle elasticity, it is still not clear over what range the in vivo elasticity values vary. The present study intends to produce further information by examining four different skeletal muscles in a group of 12 healthy volunteers in the age range of 27-38 years. The examinations were performed in the biceps brachii, the flexor digitorum profundus, the soleus and the gastrocnemius. The average shear modulus was determined to be 17.9 (+/- 5.5), 8.7 (+/- 2.8), 12.5 (+/- 7.3) and 9.9 (+/- 6.8) kPa for each muscle, respectively. To ascertain the reproducibility of the examination, the stiffness measurements in two volunteers were repeated seven times for the biceps brachii. These examinations yielded a mean shear modulus of 11.3 +/-.7 and 13.3 +/- 4.7 kPa for the two subjects. For elasticity reconstruction, an automated reconstruction algorithm is introduced which eliminates variation due to subjective manual image analysis. This study yields new information regarding the expected variation in muscle elasticity in a healthy population, and also reveals the expected variability of the MRE technique in skeletal muscle.

Adult↗

PubMed2004

Diffusive sensitivity to muscle architecture: a magnetic resonance diffusion tensor imaging study of the human calf.

The aim of this study was to examine the diffusive properties of adjacent muscles at rest, and to determine the relationship between diffusive and architectural properties, which are task-specific to muscles. The principle, second, and third eigenvalues, trace of the diffusion tensor, and two anisotropic parameters, ellipsoid eccentricity (e) and fractional anisotropy (FA), of various muscles in the human calf were calculated by diffusion tensor imaging (DTI). Linear correlations of the calculated parameters to the muscle physiological cross-sectional area (PCSA), which is proportional to maximum muscle force, were performed to ascertain any linear relation between muscle architecture and diffusivity. Images of the left calf were acquired from six healthy male volunteers. Seven muscles were investigated in this study. These comprised the soleus, lateral gastrocnemius, medial gastrocnemius, posterior tibialis, anterior tibialis, extensor digitorum longus, and peroneus longus. All data were presented as the mean and standard error of the mean (SEM). In general, differences in diffusive parameter values occurred primarily between functionally different muscles. A strong correlation was also found between PCSA and the third eigenvalue, e, and FA. A mathematical derivation revealed a linear relationship between PCSA and the third eigenvalue as a result of their dependence on the average radius of all fibers within a single muscle. These findings demonstrated the ability of DTI to differentiate between functionally different muscles in the same region of the body on the basis of their diffusive properties.

Diffusion Magnetic Resonance Imaging↗

PubMed2003

Steady-state free precession sequences in myocardial first-pass perfusion MR imaging: comparison with TurboFLASH imaging.

The aim of this study was to compare the image quality of a saturation-recovery gradient-recalled echo (GRE; TurboFLASH) and a saturation-recovery SSFP (SR-TrueFISP) sequence for myocardial first-pass perfusion MRI. Eight patients with chronic myocardial infarction and 8 volunteers were examined with a TurboFLASH (TR 2.1 ms, TE 1 ms, FA 8 degrees ) and a SR-TrueFISP sequence (TR 2.1 ms, TE 0.9 ms, FA, 50 degrees ) on a 1.5 T scanner. During injection of 0.05 mmol/kg BW Gd-DTPA at 4 ml/s, three short axis slices (8 mm) of the left ventricle (LV) were simultaneously scanned during breath-hold. Maximum signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) between infarcted and normal myocardium, and percentage signal intensity change (PSIC) were measured within the LV lumen and in four regions of the LV myocardium for the three slices separately. For the LV lumen, SR-TrueFISP was superior in SNR and PSIC (factor 3.2 and 1.6, respectively). Mean maximum SNR, PSIC, and CNR during peak enhancement in the LV myocardium were higher for SR-TrueFISP compared with TurboFLASH (factor 2.4, 1.25, and 1.24, respectively). The SNR was higher in the septal portion of the ventricle than in anterior/posterior and lateral regions. The SR-TrueFISP provides higher SNR and improves image quality compared with TurboFLASH in first-pass myocardial perfusion MRI.

Adult↗

PubMedDate not supplied

Evaluation of the three-time-point method for diagnosis of breast lesions in contrast-enhanced MR mammography.

PURPOSE: To evaluate the three-time-point (3TP) method for diagnosis of breast lesions detected on contrast-enhanced MR mammography. MATERIALS AND METHODS: MR imaging was performed in 40 women with 120 suspected breast lesions in mammography and/or sonography. The contrast kinetics was converted by 3TP software on a pixel-by-pixel basis into color-coded images. Lesion diagnosis was made by analysis of color intensity and color hue. The 3TP results were compared with the results of the region-of-interest (ROI) method. In 16 patients, we were able to correlate the results with histopathological findings. RESULTS: The 3TP method could successfully be performed in all MR mammographies. Forty (33%) lesions had a diameter of less than 5 mm, 56 (47%) lesions between 5 and 10 mm, and 24 (20%) lesions were greater than 1 cm. Of all 120 lesions, 65 (54%) showed heterogeneous contrast enhancement. In 117 (97%) of all 120 lesions the results of ROI and the automated 3TP method were considered equivalent. However, in three lesions the manual ROI differed from the 3TP method. After a second, repeated manual ROI placement, we were able to confirm equivalent results with the 3TP images as well. CONCLUSIONS: The 3TP method automatically and reliably converts contrast kinetic information of the entire breast into a color-coded image. The 3TP method presents kinetic information of the entire dynamic series in an easy-to-interpret format and this automated method may allow to forego time-consuming and sometimes subjective manual ROI placements. This method displays the heterogeneity of the contrast enhancement pattern often observed in malignant lesions and makes it usable as diagnostic criterion.

Adult↗