The purpose of this study was to assess the degree of conspicuity and amount of field distortion caused by a biopsy needle designed specifically for use in MRI studies. Toward this, a number of pulse sequences including spin and field echo were used. Parameters such as field of view, strength of read gradient, direction of read gradient, echo time and slice thickness were varied. The effect of these manipulations on needle visualization was studied. Partial voluming errors with thicker slices decreased needle conspicuity. Smaller field of view improved needle visualization as a result of magnification effect. Shallow read gradient strengths also increased needle conspicuity. Increased image artifacts were noted on field-echo sequences compared to spin echo. This effect increased with longer echo times. This reflects T2* effects on field-echo images.

Biopsy, Needle↗

PubMedDate not supplied

Automated MR imaging protocols for improved patient throughput.

The total time spent on each patient during an MR study determines patient throughput and ultimately influences MR scan charges. Actual data acquisition often represents only a small portion of this examination time. Other functions such as patient loading and unloading, positioning, coil placement, scan setup, and image reconstruction time also contribute to the total examination time. We describe a technique for creating automated imaging protocols for standard MR examinations which optimize these functions, thereby decreasing operator interventions and shortening the overall examination time. A prototype sequence for examining the larynx and neck was developed which allowed three sequential multiple slice acquisitions to be obtained in three orthogonal planes with a single operator setup step. All tuning and scan placement after this first step was done under computer control. The new sequence allowed larynx and neck studies to be performed in less than 30 min for spin echo and under 16 min for field echo instead of the 50-60 min required by previous methods. The new technique should be useful for improving patient throughput for a cariety of standardized examinations including the temporal bone, head and neck, joints, and other regions.

Computers↗

PubMedDate not supplied

Magnetic field strength dependence of chemical shift artifacts.

The dependence of proton MRI chemical shift artifacts on main magnetic field strength was investigated using three MR whole body systems from 0.3 to 1.5 T with both permanent and superconducting magnet designs. The magnetic field gradients varied from 0.09 to 1.0 gauss/cm. The image bandwidth varied from 8.54 to 32 kHz. Both phantoms and normal volunteers were studied. The chemical shift misregistration error in hertz was determined by the main magnetic field strength of the system which was proportional to the Larmor frequency. The actual image error in millimeters was determined by a combination of the shift in hertz as well as by the amplitude of the magnetic field gradients applied to form the image. Steeper gradients mapped a given shift in hertz onto a smaller millimeter displacement. The higher field strength systems tended to use steeper magnetic field gradients, but this increase was not enough to offset the higher absolute shift in hertz due to the higher Larmor frequencies. In general, the chemical shift in millimeters tended to increase with the increasing field strength despite the steeper imaging gradients. Based on these findings, strategies for minimizing the chemical shift artifact may be developed.

Adipose Tissue↗