The aim of this study was This approach, based on the time domain analysis of the radiofrequency signals, appears promising as a means to establish certain aspects of ultrasonic diagnosis on a more quantitative basis.3,4 The assessment of regional myocardial fibrosis would be of particular interest since excessive myocardial fibrosis is both an important sign and is associated with a variety of myocardial diseases.Even though there were substantial problems in comparing exactly the anatomic region interrogated by the ultrasound technique versus the same area sampled by the endomyocardial biopsy, the aim of this study was to assess in vivo whether the regional ultrasonic reflectivity, evaluated by a real-time integrated backscatter

ABSTRACT:Birdcage coils are used widely in nuclear magnetic resonance (NMR) applications for their ability to operate in transmit/receive mode with high signal-to-noise ratio (SNR) and wide field homogeneity. When used at low frequencies, a number of drawbacks arise that drastically reduce their overall performances. In this article we show how the choice of the conductors cross-geometry and capacitor quality affects the coil overall performance. Several birdcage coils, tuned at 7.66 MHz, were designed and built, using conductors with different shapes and capacitors with different quality factors. Realized coils were tested and characterized by laboratory workbench in order to extract several quality indices. In addition, experiments were done in a real magnetic resonance (MR) scanner to evaluate the field homogeneity. We show that an optimized choice of conductor shape and capacitors allows us to obtain high-quality birdcage coils tuned at frequencies in the megahertz range. Our results are applicable in several situations as MR imaging (MRI) in low-field scanners, imaging of nuclear species at intermediate fields, Overhauser systems, and prepolarized NMR.

The aim of this study in vitro of human fresh specimens was to quantitatively evaluate the contribution of the aqueous phase-intima interface (the first 400 msec of the reflected signal) in normal and atherosclerotic arterial walls. Seventy-five samples were studied, 15 normal, 15 fatty, 15 fibrofatty, 15 fibrous, and 15 calcific. A broadband transducer (4 to 14 MHz) was used. The aqueous phase-intima reflection (expressed in dB, mean + SD) was lowest in the fatty plaques (-35.3 + 2.5), differing in a highly significant way from that in all other groups: normal (-13.2 ± 8.8), fibrofatty ( -20.4 8.3), fibrous ( -13.0 ± 9.7), calcific ( -5.9 -+ 3.4). The echo coming from the intimamedia transition was of relatively low amplitude in normal and in fatty samples; typically, strong reflections from the intima-media transitions were present in the other pathologic subsets. In conclusion, the time domain echo pattern of the arterial wall may provide a useful clue to the structure of the plaque. Circulation 77, No. 3, 654-659, 1988. ULTRASONIC tissue characterization of atherosclerosis has been attempted in several studies in vitro. [1][2][3][4][5][6][7][8][9][10][11][12] The purpose of these studies has been twofold: (1) to test new variables of potential diagnostic use, and (2) to provide basic information for a better definition of limits and applicability of clinical echocardiography.Findings in vitro show that, in predominantly fatty samples of aortic wall, the values of the internal backscatter tend to overlap with those found in normal walls.9 In this previous study, the value of the specular echoes of aqueous phase-tissue interface -which is supposed to be strongly angle dependent -was purportedly "gated out." However, the detection of specular reflections is fundamental for the border identification with conventional echocardiographic instruments. 13 The aim of this study was to quantitatively evaluate the contribution of the "first interface" intimal echo in various normal and pathologic subsets of arterial wall. Materials and methodsExperimental procedure. Fresh specimens of arterial wall were taken from human aortas at autopsy and those with one of four distinct kinds of lesions (fatty, fibrofatty, fibrotic, and