B. Chapman

Improvements in snap-shot nuclear magnetic resonance imaging

New variants of the ultra-high-speed echo-planar imaging technique have been used to obtain snap-shot images of adult patients and volunteers at 0.1 T. Modified pulsed-gradient sequences together with non-linear signal sampling and activity screened gradients have greatly improved the image quality obtainable by single-shot methods. A particular variant, modulus blipped echo-planar single-pulse technique (MBEST), although slightly slower than the blipped echo-planar single-pulse technique (BEST), is experimentally more robust and incorporates intrinsic T2 weighting. An account of these improvements together with some experimental results is presented.

ECHO PLANAR IMAGING OF THE HUMAN FETUS IN UTERO AT 0.5 T

The snap-shot capability of the echo-planar imaging technique is used to freeze motion effectively in human fetal studies in utero. These first results obtained at 0.5 T demonstrate diagnostic quality images without the need for averaging. Although averaging improves the image signal to noise ratio, it is shown that significant image blurring is produced even when only eight separate images are averaged over a period of a few seconds. Results are presented showing anatomical detail of the internal organs of the fetus. Some pathology is also demonstrated. These results were obtained using the modulus blipped echo-planar single-pulse technique (MBEST). Running at 10 frames/second, the modulus version of the fast low-angle excitation echo-planar technique (FLEET) is used to produce ungated fetal cardiac movies.

Multishield active magnetic screening of coil structures in NMR

Abstract The principles of active screening of time-dependent magnetic fields introduced by Mansfield and Chapman are especially useful for screening rapidly switched gradients within the close confines of a superconductive magnet. These ideas have been extended to multiscreen structures. For two active screens it is shown that the primary field can equal its unshielded value within the inner screen, and still be fully screened outside the outer shield. It is further shown that full screening benefits obtain, even when the primary coil and first screen are coincident. This leads naturally to an integrated coil design approach which may be further generalized to incorporate the target field method of Turner.

Study of internal structure of the human fetus in utero by echo-planar magnetic resonance imaging

The ultrafast echo-planar magnetic resonance imaging technology, developed and built in Nottingham, has been used to produce the first snapshot images of the human fetus in utero. The imager, operating at a proton resonance frequency of 22 MHz, produces transaxial views in 64 or 128 milliseconds. These images comprise either 64 x 128 or 128 x 128 pixels with an in-plane resolution of 3 x 3 mm2. The slice thickness is 10 mm. Fetal scans of up to 32 contiguous slices are produced in a few minutes. These have been used to study the internal structure of the uterus and the fetus in a range of cases with gestations ranging from 26 weeks to term. Echo-planar imaging seems particularly suitable as an imaging modality since its high speed obviates image blurring arising from fetal motion.

REAL-TIME NUCLEAR MAGNETIC RESONANCE CLINICAL IMAGING IN PAEDIATRICS

Echo-planar imaging (EPI), a distinctive variant of nuclear magnetic resonance, needs only a fraction of a second for an image to be acquired and so is free from movement artifacts caused by respiration or heart beat. Clinical findings in the lungs, heart, and mediastinum of three children with high respiratory and heart rates who were examined by EPI are described.

Double active magnetic screening of coils in NMR

The principles of active screening of time dependent magnetic fields, introduced by Mansfield and Chapman (1986), have been extended to include two screens. Magnetic screening is especially useful in NMR when rapidly switched gradients are required within the close confines of a superconductive magnet. However, single screens reduce and spatially distort the field from the primary coil. With two active screens it is possible to fully screen the primary coil far field without impairing its near field spatial characteristics.

Optimized gradient pulse for use with EPI employing active acoustic control

The concept of active acoustic control was recently introduced by Mansfield and Haywood (MAGMA 2000:10:147–151) to ameliorate the problem of acoustic noise from MRI, particularly that from high‐speed EPI. A 30 dB reduction in noise was previously achieved with the use of acoustic control operating at spot frequencies within a narrow band. In this work, a new acoustic gradient pulse is introduced that comprises an oscillating gradient of finite duration, incorporating a combination of frequencies within this band designed for use as the switched read gradient in echo‐planar imaging (EPI). Employing this pulse with active acoustic control results in a reduction of acoustic noise by 50 dB. Magn Reson Med 50:931–935, 2003.

Snap-shot magnetic resonance imaging at 0.1 T using double-screened gradients

Abstract Recent advances in coil design have permitted single-shot acquisition of 128 × 128 pixel adult body images in 65 ms using echo-planar MRI. These developments are described, including double screening of the gradient coils to eliminate induced eddy currents, while maintaining high coil efficiency. Modulus images with excellent T 2 contrast obtained by a modified echo-planar imaging sequence, MBEST, are also presented.

Echo planar imaging of an infant with pectus excavatum.

Echo planar imaging has enabled us to image safely and without sedation the thorax of an infant with pectus excavatum deformity. The heart was displaced into the left side of the thorax, and the right lung was calculated to be 1.6 times larger than the left lung.

Induced fluid movement within a giant ovarian cyst demonstrated by echo- planar imaging

Over 50% of ovarian tumours are of epithelial origin occurring as solid carcinomas and mucinous or serous cysts, the majority of which can be readily categorized as benign or malignant. However, approximately onefifth of the cysts, whilst showing some histological feature of malignancy, lack evidence of stromal invasion and are therefore reported as borderline malignancy. Serous cystadenomas may be unilocular or multilocular and vary in size from a few centimetres to enormous dimensions where they come to occupy most of the pelvis and abdominal cavity. In approximately 50% of cases the tumours are bilateral. Some have intracystic papillary ingrowths or solid areas in one or more loculi, and invasion of the cyst wall with tumour extension onto the serosal surface indicates the transition from a cystadenoma to a cystadenocarcinoma. A giant serous cyst of the ovary has been imaged by echo-planar imaging (EPI) (Mansfield, 1977) and the features observed compared with the operative and pathological findings. T...