Hiram Baddeley

Is ultrasonography useful in the assessment of diffuse parenchymal liver disease

One hundred twenty-five patients investigated at the Royal Brisbane Hospital, who underwent both hepatic ultrasonography and liver biopsy between 1980 and 1983, were scored quantitatively for ultrasound features of loss of detail, echogenicity, and attenuation, as well as for histologic features of fat, fibrosis, and inflammation. Strong correlations were found between the score for fat content and each of the three ultrasound features, and between the score for hepatic fibrosis and loss of detail and echogenicity, but there was no strong correlation with attenuation. Hepatic inflammation did not correlate with any of the ultrasound features. The correlations for fat were strongest when the interval between ultrasonography and liver biopsy was less than or equal to 7 days. Although ultrasonography had a positive predictive value of 98% in the diagnosis of diffuse parenchymal abnormality, it did not distinguish fat from fibrosis nor reliably diagnose cirrhosis. Ultrasonography gave false-positive results in only 2 patients, but in 17 patients, false-negative ultrasound examinations were encountered. These findings indicate that ultrasound is not a useful screening investigation for parenchymal liver disease, nor is it useful in gauging hepatic pathology. However, abnormal hepatic ultrasonography in patients with suspected liver disease strongly suggests the presence of diffuse liver disease.

Water signal elimination in vivo, using suppression by mistimed echo and repetitive gradient episodes

A number of techniques (I) are available for the elimination of an unwanted signal (usually the ‘H signal from water) from a spectrum. Unless the unwanted signal is removed before the preamplifier and ADC are encountered in the signal detection pathway, difficulties are experienced in the observation of very weak signals because of dynamic range problems. O f the available techniques the most efficient appears to be the 1331 method developed by Hore (I, 2); however, as Hore points out, this technique is only of limited value if the water resonance is broad. This is the situation often encountered in vivo where very broad water signals are observed, the broadness usually being the result of magnetic field inhomogeneity. In general, for signal elimination the most successful methods have in the past relied on overall nonexcitation of the unwanted resonance, the aim being to leave the unwanted spin coherence along the z axis and away from the detection plane. The alternative procedure would be to destroy selectively the unwanted spin coherence and it is this strategy which has led to the application of reverse polarization transfer methods (3) as probably the most efficient water signal elimination method yet devised. In this paper we develop a method for selectively destroying the water signal, applicable to in vivo NMR studies where broad water signals are often encountered. We call the technique SUBMERGE. The method eliminates transverse water spin coherence over a wide but controllable frequency band. The significant point is that the water spin coherence is destroyed, thus eliminating the signal from the preamplifier and ADC, allowing the efficient detection of weak signals. As a test, we attempt to observe the methyl signal from lactic acid at a concentration of 10 mM in neat HzO. The water signal is thus about 3700 times more intense than the signal of interest. A 250 ml round-bottom flask was used as the sample container. A water signal having a half-height width of 10 Hz was typically detected in a single pulse experiment. In Fig. 1 is shown the experimentally determined excitation profile from a 10 ms 7r/2 sine pulse. The excitation profile from a 10 ms 7r/2 gaussian pulse is also shown for comparison. At a ‘H resonance frequency of 100 MHz (field strength 2.4 T) the chemical-shift separation between the two resonances of interest is about 345 Hz. Thus, by use of such shaped pulses, it is possible to excite the water signal but not the

Magnetic resonance imaging in gastroenterology and hepatology

Magnetic resonance (MR) properties of materials were first discovered 40 years ago’-3 and have been used for MR spectroscopy, particularly in chemical research, since that time. In 1973 Lauterbur4 suggested that these properties might be used for clinical imaging and the first MR images of living human anatomy were produced 4 years later.5’6 In the years since 1977 there has been a progressive improvement in radiofrequency (rf) pulsing techniques, computer hardware, software and magnet design which has made MR imaging (MRI) a potentially powerful diagnostic tool in clinical medicine.