William H. Perman

Quality assurance methods and phantoms for magnetic resonance imaging: report of AAPM nuclear magnetic resonance Task Group No. 1.

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Improved detectability in low signal-to-noise ratio magnetic resonance images by means of a phase-corrected real reconstruction.

We show that for magnetic resonance (MR) images with signal-to-noise ratio (SNR) less than 2 it is advantageous to use a phase-corrected real reconstruction, rather than the more usual magnitude reconstruction. We discuss the results of the phase correction algorithm used to experimentally verify the result. We supplement the existing literature by presenting closed form expressions (in an MR context) for the probability distribution and first moments of the signal resulting from a magnitude reconstruction.

Evaluation of a prototype dual‐energy computed tomographic apparatus. II. Determination of vertebral bone mineral content

A prototype dual-energy computed tomographic (CT) scanner (Siemens Somatom DR3) with rapid kVp switching and prereconstruction processing has been used to measure vertebral bone mineral density. With this approach misregistration and beam hardening inaccuracies can be reduced considerably. Basis material images of aluminum- and Lucite-equivalent density enable measurements of bone mineral density that are nearly independent of the amount of marrow fat. To simulate variable marrow fat, alcohol-water mixtures were used as media in calibration standards. A section of dried trabecular bone was also scanned immersed in varying alcohol-water mixtures. In both simulations it was shown that the dual-energy measurement is nearly independent of marrow composition whereas the single-energy measurement would be strongly influenced by marrow fat. Dual-energy CT was compared to dual-photon absorptiometry (153Gd) for the measurement of bone mineral mass of ten excised human vertebrae. There was a high degree of correlation between the two measurements (r = 0.97). Dual-energy and single-energy CT measurements on 17 patients with suspected metabolic bone disease strongly support the conclusion that the influence of fat can lead to significant errors in single-energy determinations of the mineral density of trabecular bone.

Regional T2 and Sodium Concentration Estimates in the Normal Human Brain by Sodium-23 Mr Imaging at 1.5 T

We have analyzed multiple spin echo Na magnetic resonance (MR) images of the normal human brain in four volunteer subjects. Utilizing the much slower T2 decay of the CSF, we obtained images that separate cortex from the surrounding CSF and measured regional T2 of cortex, white matter, CSF, vitreous humor, and superior sagittal sinus. Assuming a sodium concentration of 145 mM in the vitreous humor, we normalized the extrapolated equilibrium magnetization (M0) for each region to the M0 of the vitreous humor to estimate regional sodium concentration. We found that regional T2 measurements more consistently distinguish the high signal regions of cortex, CSF, and blood than do our regional sodium estimates, whereas regional sodium estimates adequately distinguish white matter from cortex. The T2 values of white matter and cortex, on the other hand, are nearly identical. Our work addresses the problems encountered in establishing norms for clinical application of Na MR and represents a step toward establishing those norms.

Pulse sequence generated oblique magnetic resonance imaging: Applications to cardiac imaging

A pulse sequence procedure for producing oblique magnetic resonance images is described. Using this procedure we present a new, accurate method to obtain true short-axis views and true long-axis views (both parallel and perpendicular to the septal plane) of the heart. The method is accurate regardless of the orientation of patients heart. The method does not require the patient to be rotated, nor otherwise moved, and does not require any additional hardware. The method is experimentally verified with both human and phantom studies. The phantom study indicates accuracy of approximately 1 degree with a commercial scanner that reports angular measurements to a precision of 1 degree. Application of the short-axis views to measurement of left ventricular volume, and possible advantages of Gauss-Legendre integration for this measurement are discussed. Finally, multiphase oblique cardiac images are presented.

Oblique magnetic resonance imaging of the bronchi

The trachea and main bronchi of a supine patient in a magnetic resonance (MR) scanner are not contained in a single standard coronal plane, but instead intersect this coronal plane at some angle, usually 20 degrees - 35 degrees. We have developed a new MR imaging protocol to determine the oblique imaging plane which best contains the trachea and main bronchi. The resulting oblique images simplify anatomical identification, and allow the user to select additional oblique planes which cut any desired portion of main bronchus in true cross section. Accurate lumen shapes and areas may then be extracted from these cross-sectional images. The method does not require the patient to be moved or rotated, and does not require hardware modification. We demonstrate the clinical application of the protocol with both a normal volunteer and a patient with an endobronchial tumor. The use of gradient echo pulse sequences together with this protocol to distinguish between vessels and bronchi is presented. We provide phantom verification to demonstrate the quantitative accuracy of the method to provide lumen areas.