Alto Stemmer

Diffusion-weighted imaging of the liver: comparison of navigator triggered and breathhold acquisitions.

To compare a free breathing navigator triggered single shot echoplanar imaging (SS EPI) diffusion‐weighted imaging (DWI) sequence with prospective acquisition correction (PACE) with a breathhold (BH) DWI sequence for liver imaging.

Magnetic resonance imaging of the upper abdomen using a free-breathing T2-weighted turbo spin echo sequence with navigator triggered prospective acquisition correction.

To evaluate a free‐breathing navigator triggered T2‐weighted turbo spin‐echo sequence with prospective acquisition correction (T2w‐PACE‐TSE) for MRI of the upper abdomen in comparison to a conventional T2‐weighted TSE (T2w‐CTSE), a single‐shot TSE (T2w‐HASTE), and a T1‐weighted gradient‐echo sequence (T1w‐FLASH).

Tumor detection by Diffusion Weighted MRI and ADC-Mapping - Initial Clinical Experiences in Comparison to PET-CT

Objective:To evaluate the clinical potential of diffusion-weighted-imaging (DWI) with apparent diffusion coefficient (ADC)-mapping for tumor detection. Materials and Methods:A single-shot echo-planar-imaging DWI sequence with fat suppression and ability for navigator-based respiratory triggering was implemented. Nineteen patients (11 melanoma, 4 prostate cancer, 1 non-Hodgkin lymphoma, and 3 lung cancer) were examined by positron emission tomography (PET) with an integrated computed tomography scanner (PET-CT) and DWI. Images at b = 0, 400, and 1000 s/mm2 were acquired and ADC maps were generated. PET examinations were used as a reference for tumor detection. Four hundred twenty-four regions of interest were used for DWI and 73 for PET data evaluation. Results:DWI and ADC maps were of diagnostic quality. Metastases with increased tracer uptake were clearly visualized at b = 1000 s/mm2 with the exception of mediastinal lymph node metastases in cases of lung cancer. ADC mapping did not improve detection rates. Conclusions:DWI is a feasible clinical technique, improving the assessment of metastatic spread in routine magnetic resonance imaging examinations.

High-resolution MR-imaging of the liver with T2-weighted sequences using integrated parallel imaging: comparison of prospective motion correction and respiratory triggering.

To compare high‐resolution T2‐weigthed images of the liver with and without integrated parallel acquisition techniques (iPAT) using either breath‐hold sequences in combination with prospective acquisition motion correction (PACE) or respiratory triggering.

T2 measurement of the human myocardium using a T2-prepared transient-state TrueFISP sequence.

A fast and motion‐insensitive technique suitable for myocardial BOLD contrast imaging is presented. The method, termed T2‐TrueFISP, combines T2 magnetization preparation with steady‐state free precession (SSFP) imaging for T2 relaxation mapping of the myocardium in healthy volunteers. The T2 contrast‐to‐noise ratio (CNR) was optimized with the use of transient‐state TrueFISP readout and half‐Fourier readout with linear phase encoding. Single‐slice myocardial T2‐weighted image was obtained within one heartbeat, and a single slice T2 map of the myocardium was obtained in under 5–7 s. A respiratory navigator‐gating method was incorporated for serial measurements and signal averaging, with the subjects breathing freely. The mean myocardial T2 relaxation time measured in 12 healthy volunteers was 54 ± 5.7 ms. Regional variations of T2 values across the myocardium were 7%. Temporal variations across serial T2 measurements in a transmural region covering ∼0.5 cc of the left ventricular (LV) wall were 3.6% without signal averaging (number of excitations (NEX) = 1) and 1.7% with signal averaging (NEX = 10). According to our preliminary results, the T2‐TrueFISP method is expected to provide a robust and sensitive tool for clinical application of myocardial BOLD contrast imaging. Magn Reson Med 57:960–966, 2007.

Brain magnetic resonance imaging at 3 tesla using BLADE compared with standard rectilinear data sampling

Objectives:We sought to evaluate Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction (PROPELLER; BLADE) data acquisition in comparison with standard k-space sampling techniques for axial and sagittal brain imaging at 3 T regarding imaging artifacts. Material and Methods:Forty patients who gave consent were included in a prospective comparison of standard and PROPELLER (BLADE) k-space sampling techniques. All examinations were performed at 3 T with comparison of standard T2-weighted fluid-attenuated inversion recovery (FLAIR) to PROPELLER T2-weighted FLAIR in the axial image orientation and standard T1-weighted gradient echo to PROPELLER T1-weighted FLAIR in the sagittal image orientation. Imaging protocols were matched for spatial resolution, with data evaluation performed by 2 experienced neuroradiologists. Image data were compared regarding various image artifacts and overall image quality. Reader agreement was assessed by Cohens kappa statistics. Results:PROPELLER T2-weighted axial data acquisition showed significantly less pulsation and Gibbs artifacts than the standard T2-weighted scan. Even without motion correction, the frequency of ghosting (motion) artifacts was substantially lower in the PROPELLER T2-weighted data and readers concordantly (κ = 1) rated PROPELLER as better than or equal to the standard T2-weighted scan in the majority of cases (95%; P < 0.0001). In the comparison of sagittal T1-weighted data sets, readers showed only fair agreement (κ = 0.24) and noted consistent wrap artifacts in PROPELLER T1-weighted FLAIR. Conclusion:PROPELLER (BLADE) brain magnetic resonance imaging is also applicable at 3 T. In addition to minimizing motion artifacts, the PROPELLER acquisition scheme reduces other magnetic resonance artifacts that would otherwise degrade scan quality.

High Spatial Resolution T1-weighted Mr Imaging of Liver and Biliary Tract During Uptake Phase of a Hepatocyte-specific Contrast Medium

Objectives:The hypothesis for this prospective study was that T1-weighted respiratory triggered high spatial resolution images of the liver acquired during the uptake phase of a hepatobiliary contrast medium are technically feasible and provide significantly improved image quality compared with breath-hold images. Materials and Methods:An inversion recovery-prepared spoiled gradient echo sequence was developed that can be obtained with respiratory triggering. This sequence was acquired in 20 patients with a total of 41 focal liver lesions and compared with axial and coronal breath-hold spoiled gradient echo sequences. All 3 sequences were obtained in the hepatobiliary phase after intravenous injection of Gd-EOB-DTPA at a dosage of 0.025 mmol/kg of body weight. Quantitative evaluation measured the contour sharpness index of the common bile duct and calculated the relative contrast between liver lesions (common bile duct, respectively) and liver parenchyma. In the qualitative assessment, 2 readers independently scored the depiction of focal liver lesions and 3 segments of the biliary tract, the sharpness of hepatic vessels, and the level of artifacts. Statistical significance was assumed at P < 0.05. Results:The respiratory-triggered sequence was technically successful in all 20 patients, revealed significantly higher liver-lesion contrast, contour-sharpness index and scores for depiction of focal liver lesions, biliary tree, and sharpness of hepatic vessels compared with the respective breath-hold sequence. The relative contrast between the common bile duct and the liver parenchyma was significantly higher for the coronal breath-hold sequence compared with the respiratory-triggered sequence. No significant difference was found with respect to the level of artifacts. The 2 readers agreed in 77.9% of the qualitative assessments. Conclusions:T1-weighted respiratory triggered high spatial resolution images obtained in the hepatobiliary phase are technically feasible and significantly improve the image quality compared with breath-hold images.

Contrast-enhanced T1-weighted fluid-attenuated inversion-recovery BLADE magnetic resonance imaging of the brain: an alternative to spin-echo technique for detection of brain lesions in the unsedated pediatric patient?

RATIONALE AND OBJECTIVES We compared contrast-enhanced T1-weighted magnetic resonance (MR) imaging of the brain using different types of data acquisition techniques: periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER, BLADE) imaging versus standard k-space sampling (conventional spin-echo pulse sequence) in the unsedated pediatric patient with focus on artifact reduction, overall image quality, and lesion detectability. MATERIALS AND METHODS Forty-eight pediatric patients (aged 3 months to 18 years) were scanned with a clinical 1.5-T whole body MR scanner. Cross-sectional contrast-enhanced T1-weighted spin-echo sequence was compared to a T1-weighted dark-fluid fluid-attenuated inversion-recovery (FLAIR) BLADE sequence for qualitative and quantitative criteria (image artifacts, image quality, lesion detectability) by two experienced radiologists. Imaging protocols were matched for imaging parameters. Reader agreement was assessed using the exact Bowker test. RESULTS BLADE images showed significantly less pulsation and motion artifacts than the standard T1-weighted spin-echo sequence scan. BLADE images showed statistically significant lower signal-to-noise ratio but higher contrast-to-noise ratios with superior gray-white matter contrast. All lesions were demonstrated on FLAIR BLADE imaging, and one false-positive lesion was visible in spin-echo sequence images. CONCLUSION BLADE MR imaging at 1.5 T is applicable for central nervous system imaging of the unsedated pediatric patient, reduces motion and pulsation artifacts, and minimizes the need for sedation or general anesthesia without loss of relevant diagnostic information.

Comparison of physiological triggering schemes for diffusion‐weighted magnetic resonance imaging in kidneys

To determine the potential benefit of combined respiratory‐cardiac triggering for diffusion‐weighted imaging (DWI) of kidneys compared to respiratory triggering alone (RT).

Diffusion-weighted imaging in patients with acute brain ischemia at 3 T: current possibilities and future perspectives comparing conventional echoplanar diffusion-weighted imaging and fast spin echo diffusion-weighted imaging sequences using BLADE (PROPELLER).

Objectives:To compare diffusion-weighted imaging (DWI) based on a fast spin echo (FSE) sequence using BLADE (PROPELLER) with conventional DWI-echoplanar imaging (EPI) techniques at 3 T and to demonstrate the influence of hardware developments on signal-to-noise ratio (SNR) with these techniques using 12- and 32-channel head coils. Materials and Methods:Fourteen patients with brain ischemia were evaluated with DWI using EPI and FSE BLADE sequences, with a 12-channel head coil, in the axial plane and 1 additional plane (either sagittal or coronal). SNR and CNR were calculated from region-of-interest measurements. Scans were evaluated in a blinded fashion by 2 experienced neuroradiologists. SNR of both DWI techniques was evaluated in 12 healthy volunteers using different parallel imaging (PI) factors (for the EPI sequence) and both the 12- and 32-channel coils. Results:DWI-BLADE sequences acquired with the 12-channel coil revealed a significant reduction in SNR (mean ± SD) of ischemic lesions (SNRlesion [5.0 ± 2.5]), normal brain (SNRbrain [3.0 ± 1.9]), and subsequently in CNR (3.0 ± 1.8) as compared with the DWI-EPI sequence (SNRlesion [9.3 ± 5.2], SNRbrain [7.7 ± 3.5], CNR [6.1 ± 2.8], P < 0.001). Despite this reduction in SNR and CNR, the blinded read revealed a marked preference for the DWI-BLADE sequence, or equality between the sequences, in the majority of patients because lesion detection was degraded by susceptibility artifacts on axial DWI-EPI scans in 14% to 43% of cases (but in no instance with the DWI-BLADE sequence). In particular, preference for the DWI-BLADE sequence or equality between the 2 techniques for lesion detection in the brainstem and cerebellum was observed. On some DWI-BLADE scans, in the additional plane, radial-like artifacts degraded lesion detection.In volunteers, SNR was significantly improved using the 32-channel coil, irrespective of scan technique. Comparing DWI-EPI acquired with the 12-channel coil (iPAT = 2) to DWI-BLADE acquired with the 32-channel coil, comparable SNR values were obtained. The 32-channel coil also makes feasible, with DWI-EPI, an increase in the PI factor to 4, which allows for a further reduction of bulk susceptibility artifacts. However, still DWI-BLADE sequences performed better because of absence of bulk susceptibility artifacts at comparable SNR values. Conclusion:Despite lower SNR at comparable PI factors, DWI-BLADE sequences acquired using the 12-channel coil are preferable in most instances, as compared with DWI-EPI sequences, because of the absence of susceptibility artifacts and subsequently improved depiction of ischemic lesions in the brainstem and cerebellum. With the 32-channel coil, recently FDA approved, DWI-BLADE acquired with an iPAT = 2 provides comparable SNR without bulk susceptibility artifacts as compared with the DWI-EPI sequences acquired for clinical routine to date and has the potential to replace the standard DWI technique for special indications like DWI of the cerebellum and the brainstem or in presence of metallic implants or hemorrhage.