David Grodzki

Ultrashort echo time imaging using pointwise encoding time reduction with radial acquisition (PETRA).

Sequences with ultrashort echo times enable new applications of MRI, including bone, tendon, ligament, and dental imaging. In this article, a sequence is presented that achieves the shortest possible encoding time for each k‐space point, limited by pulse length, hardware switching times, and gradient performance of the scanner. In pointwise encoding time reduction with radial acquisition (PETRA), outer k‐space is filled with radial half‐projections, whereas the centre is measured single pointwise on a Cartesian trajectory. This hybrid sequence combines the features of single point imaging with radial projection imaging. No hardware changes are required. Using this method, 3D images with an isotropic resolution of 1 mm can be obtained in less than 3 minutes. The differences between PETRA and the ultrashort echo time (UTE) sequence are evaluated by simulation and phantom measurements. Advantages of pointwise encoding time reduction with radial acquisition are shown for tissue with a T2 below 1 ms. The signal to noise ratio and Contrast‐to‐noise ratio (CNR) performance, as well as possible limitations of the approach, are investigated. In‐vivo head, knee, ankle, and wrist examples are presented to prove the feasibility of the sequence. In summary, fast imaging with ultrashort echo time is enabled by PETRA and may help to establish new routine clinical applications of ultrashort echo time sequences. Magn Reson Med, 2012.

Correcting slice selectivity in hard pulse sequences.

Many MRI sequences use non-selective hard pulse excitation in the presence of imaging gradients. In this work, we investigate to which extent the sinc-shaped frequency excitation profiles of the pulse can be used for imaging without the generation of artefacts. A correction algorithm is proposed that eliminates the influence of the excitation profile. Phantom as well as in vivo measurements prove that enhanced image quality can be obtained as long as the first minimum of the excitation profile lies outside the imaged object.

Quiet T1-weighted imaging using PETRA: Initial clinical evaluation in intracranial tumor patients

To compare the lesion contrast and signal to noise ratio (SNR) obtained with T1‐weighted pointwise encoding time reduction with radial acquisition (PETRA) to those of Magnetization‐Prepared RApid Gradient‐Echo (MPRAGE) for contrast‐enhanced imaging of primary and metastatic intracranial tumors, and to investigate whether PETRA is able to reduce acoustic noise for improved patient comfort.

Sequence-based acoustic noise reduction of clinical MRI scans.

Clinical MRI patients typically experience elevated acoustic noise levels of 80–110 dB(A). In this study, standard clinical turbo spin echo (TSE) and gradient echo (GRE) sequences were optimized for reduced acoustic noise at preserved diagnostic image quality.

MR neurographic orthopantomogram: Ultrashort echo-time imaging of mandibular bone and teeth complemented with high-resolution morphological and functional MR neurography

Panoramical radiographs or cone‐beam computed tomography (CT) are the standard‐of‐care in dental imaging to assess teeth, mandible, and mandibular canal pathologies, but do not allow assessment of the inferior alveolar nerve itself nor of its branches. We propose a new technique for “MR neurographic orthopantomograms” exploiting ultrashort echo‐time (UTE) imaging of bone and teeth complemented with high‐resolution morphological and functional MR neurography.

Arterial spin labeled carotid MR angiography: A phantom study examining the impact of technical and hemodynamic factors

To quantify the accuracy of three‐dimensional (3D) radial arterial spin labeled (ASL) magnetic resonance angiography (MRA) using vascular models of carotid stenosis.

Projection MR imaging of peripheral arterial calcifications

Both CT and MR angiography are accurate for the evaluation of luminal abnormalities in peripheral arterial disease (PAD). However, only CT (requiring exposure to potentially hazardous ionizing radiation) provides a reliable means to detect vascular calcifications. In this study, we demonstrate the feasibility of detecting peripheral arterial calcifications with MRI.

Parallel imaging-based reduction of acoustic noise for clinical magnetic resonance imaging.

ObjectivesThe objective of this study was to demonstrate the feasibility of improving perceived acoustic comfort for a standard clinical magnetic resonance imaging protocol via gradient wave form optimization and validate parallel imaging as a means to achieve a further reduction of acoustic noise. Materials and MethodsThe gradient wave forms of a standard T2 axial turbo spin-echo (TSE) sequence in head examinations were modified for acoustic performance while attempting to keep the total acquisition and inter-echo spacing the same. Parallel imaging was then used to double the inter-echo spacing and allow further wave form optimization. Along with comparative acoustic noise measurements, a statistical analysis of radiologist scoring was conducted on volumes from standard and modified sequences acquired from 10 patients after informed consent was obtained. ResultsCompared with TSE, significant improvement of acoustic comfort was measured for modified-sequences quiet TSE and quiet TSE with generalized autocalibrating partially parallel acquisitions (P = 0.0034 and P = 0.0003, respectively), and no statistically significant difference in diagnostic quality was observed without the use of parallel imaging. ConclusionsStandard clinical magnetic resonance imaging protocols can be made quieter through adequate gradient wave form optimization. In scans with high signal-to-noise ratio, parallel imaging can be used to further reduce acoustic noise.

PETRA, MSVAT-SPACE and SEMAC sequences for metal artefact reduction in dental MR imaging

ObjectivesDental MRI is often impaired by artefacts due to metallic dental materials. Several sequences were developed to reduce susceptibility artefacts. Here, we evaluated a set of sequences for artefact reduction for dental MRI for the first time.MethodsArtefact volume, signal-to-noise ratio (SNR) and image quality were assessed on a 3-T MRI for pointwise encoding time reduction with radial acquisition (PETRA), multiple-slab acquisition with view angle tilting gradient, based on a sampling perfection with application-optimised contrasts using different flip angle evolution (SPACE) sequence (MSVAT-SPACE), slice-encoding for metal-artefact correction (SEMAC) and compared to a standard SPACE and a standard turbo-spin-echo (TSE) sequence. Field-of-view and acquisition times were chosen to enable in vivo application. Two implant-supported prostheses were tested (porcelain fused to metal non-precious alloy and monolithic zirconia).ResultsSmallest artefact was measured for TSE sequences with no difference between the standard TSE and the SEMAC. MSVAT-SPACE reduced artefacts about 56% compared to the standard SPACE. Effect of the PETRA was dependent on sample used. Image quality and SNR were comparable for all sequences except PETRA, which yielded poor results.ConclusionThere is no benefit in terms of artefact reduction for SEMAC compared to standard TSE. Usage of MSVAT-SPACE is advantageous since artefacts are reduced and higher resolution is achieved.Key Points• SEMAC is not superior to TSE in terms of artefact reduction.• MSVAT-SPACE reduces susceptibility artefacts while maintaining comparable image quality.• PETRA reduces susceptibility artefacts depending on material but offers poor image quality

Quiet diffusion-weighted head scanning: Initial clinical evaluation in ischemic stroke patients at 1.5T.

To compare the quality and diagnostic value of routine single‐shot, echo‐planar imaging, diffusion‐weighted imaging (ss‐EPI‐DWI) to those of quiet readout segmented EPI‐DWI (q‐DWI) in magnetic resonance imaging (MRI) of acute stroke.