Biomedical subjects

Alto Stemmer

Publications and source records attributed to Alto Stemmer.

5 recordsLinked to original sources

PubMed2006

Respiratory-triggered MRCP applying parallel acquisition techniques.

PURPOSE: To evaluate the influence of parallel imaging on the image quality of respiratory triggered magnetic resonance cholangiopancreatography (MRCP). MATERIALS AND METHODS: A total of 30 consecutive patients underwent MRCP applying a respiratory triggered T2-weighted (T2w) turbo spin-echo (TSE) sequence without and with parallel imaging (acceleration factor of 2). Acquisition times of both sequences were recorded. Quantitative evaluation included measurement of a contour sharpness index of two segments of the pancreaticobiliary tree as well as calculation of the relative contrast between ductal structures and organ parenchyma at four different segments. The qualitative evaluation was performed by two independent radiologists who graded overall image quality, depiction of eight segments of the pancreaticobiliary tree, and the frequency of artifacts. RESULTS: The application of parallel imaging significantly (P<0.05) reduced the acquisition time of the respiratory triggered MRCP sequence by 37.7% (six minutes and two seconds+/-one minute and 26 seconds vs. three minutes and 46 seconds+/-58 seconds). The quantitative and qualitative evaluation revealed no statistically significant differences between the two sequences (P>0.05). The frequency of artifacts was at the same level for both sequences as well. CONCLUSION: The application of parallel imaging for respiratory triggered MRCP significantly reduces the acquisition time without relevant influence on image quality.

Adult↗

PubMed2006

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 Cohen's kappa statistics. RESULTS: PROPELLER T2-weighted axial data acquisition showed significantly less pulsation and Gibb's 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 (kappa = 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 (kappa = 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.

Adult↗

PubMed2005

Magnetic resonance cholangiopancreatography using a free-breathing T2-weighted turbo spin-echo sequence with navigator-triggered prospective acquisition correction.

PURPOSE: The objective of this study was to evaluate the image quality of a respiratory-triggered T2-weighted (T2w) turbo spin-echo (TSE) sequence for magnetic resonance cholangiopancreatography (MRCP) using a new method for respiratory triggering by tracking the motion of the right diaphragm [prospective acquisition correction (PACE) technique]. MATERIALS AND METHODS: Fifty consecutive patients underwent MRCP imaging applying breath-hold half-Fourier single-shot TSE sequences and the respiratory-triggered T2w TSE sequence. Qualitative evaluation grading the depiction of eight segments of the pancreaticobiliary tree and the frequency of artifacts was performed. Quantitative evaluation included calculation of the relative contrast (RC) between fluid-filled ductal structures and organ parenchyma at four segments. RESULTS: A significantly higher (P<.01) RC was measured for the respiratory-triggered T2w TSE sequence [maximum intensity projection (MIP)] for all of the four investigated segments (one of four segments for the MIP) of the pancreaticobiliary tree, as well as a significant (P<.01) improvement of visualization of all ductal segments compared with the breath-hold sequences. The frequency of artifacts was significantly lower (P<.01) compared with the breath-hold sequences. CONCLUSION: Respiratory-triggered MRCP using a T2w TSE sequence with PACE significantly improves image quality and may be included into the routine MRCP sequence protocol.

Adult↗

PubMed2005

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

PURPOSE: 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). MATERIALS AND METHODS: A total of 40 consecutive patients were examined at 1.5 T using free-breathing T2w-PACE-TSE, free-breathing T2w-CTSE, and breath-hold T2w-HASTE and T1w-FLASH acquisition. Images were evaluated qualitatively by three radiologists regarding motion artifacts, liver-spleen contrast, depiction of intrahepatic vessels, the pancreas and the adrenal glands, and overall image quality on a four-point scale. Quantitative analysis of the liver-spleen contrast was performed. RESULTS: Depiction and sharpness of intrahepatic vessels were rated significantly better (P < 0.01) using T2w-PACE-TSE compared to T2w-CTSE and T2w-HASTE sequences. Significantly higher contrast values were measured for T2w-PACE-TSE images compared to T2w-CTSE, T2w-HASTE, and T1w-FLASH images (P < 0.01). Mean examination time of the T2w-PACE-TSE was 7.91 minutes, acquisition time of the T2w-CTSE sequence was 4.52 minutes. CONCLUSION: Prospective acquisition correction is an efficient method for reducing respiratory movement artifacts in T2w-TSE imaging of the upper abdomen. Compared to T2w-CTSE and T2w-HASTE sequences recognition of anatomical details and contrast can be significantly improved.

Abdomen↗

PubMed2004

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

PURPOSE: To compare high-resolution T2-weighted 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. MATERIALS AND METHODS: Ten volunteers and 10 patients underwent each four different high-resolution fast spin echo (FSE) T2-weighted sequences with 5 mm slice thickness and a full 320 matrix: a multi-breath-hold FSE sequence with and without iPAT and PACE and a respiratory-triggered FSE sequence with and without iPAT. Image quality was rated with a five-point scale by two independent readers. Signal intensity measurements were performed on a water phantom. RESULTS: The sequences with iPAT required a substantially shorter acquisition time without loss of image quality. Overall image quality was rated equal for all sequences by both readers. Image time for nine slices with iPAT was 13 seconds (19 seconds without iPAT) with multi-breath-hold and on average 4:00 minutes (7:02 minutes without iPAT) with respiratory triggering. Imaging with the PACE technique resulted in more correct positioning of the image stacks. CONCLUSION: T2-weighted fast imaging with iPAT is feasible and results in high-quality images within a short acquisition time. Overall image quality is not negatively affected by iPAT.

Adult↗