ISSN:0094-2405    

DOI:10.1002/j.2473-4209.1979.tb36126.x

出版商:Wiley    

年代:1998

数据来源: WILEY

摘要:

This paper describes a method for imaging biosystems using radiation in the microwave frequency range (3.9 GHz). The advantages of interrogation with microwave radiation are discussed in terms of its physiological significance. An electromechanical scanning system for imaging isolated organs and the subsequent image processing techniques are described. Imagery is presented for a phantom target and an isolated canine kidney. The kidney images are interpreted in terms of the known anatomical and functional organization of the organ. It does appear to be possible to distinguish cortex corticis corresponding to a high proportion of proximal and distal convoluted tubules, deeper cortical layers corresponding to a high population density of glomeri, a medullary outer zone corresponding to the loops of Henle as well as the collecting system, and the region of calyces/renal pelvis.

ISSN:0094-2405    

DOI:10.1118/1.594595

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Total transmitted power and intensity distributions from diagnostic ultrasound systems have been measured with a radiation force balance and with a miniature hydrophone and instrumentation available in many medical centers. In assessing the accuracy of absolute intensity and power determinations from measurements of acoustic pressure with a hydrophone, ultrasonic power was computed from hydrophone measurements. This power value was compared with the power determined by a radiation force technique. On five pulse echo ultrasound systems, the ratio of the power measured with a radiation force balance to the power determined with the hydrophone varied from 0.25 to 5.5. These differences are attributed mainly to the known large variations in hydrophone response as a function of frequency, and possibly time, since several other possible sources of error were evaluated and estimated to have a reasonably small net effect of 25%. The errors evaluated were those dealing primarily with measurement procedures.

ISSN:0094-2405    

DOI:10.1118/1.594596

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Conventional approaches to computed tomography involve scanning the entire cross section and producing an image whose spatial and density resolution is uniform over its entire area. If the extent of each scan is restricted to the width of the lesion being investigated, then the x‐ray dose is reduced, but a set of incomplete “truncated” projections is measured. Conversely, projections are “hollow” when their inner parts cannot be measured, e.g., when there is a metallic object within the body cross section. We present procedures for preprocessing incomplete projections so that images can be reconstructed from them using the convolution/back projection method.

ISSN:0094-2405    

DOI:10.1118/1.594519

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Dual energy CT scanning (tomochemistry) has been proposed as a method for determining various parameters relating to the elemental composition of the tissues. In this paper, our aim is to study the relative noise inherent in two proposed techniques for dual energy scanning: a “two crystal” technique and a “two kV” technique. In the two crystal technique, a split crystal detector is used to simultaneously obtain the high and low energy data during one scan at high kV. The two kV technique requires two scans taken with widely different kV settings. We first review three commonly used approaches for utilizing the scan data to compute the relevant parameters. A theoretical formalism is constructed which aids in understanding these methods. Then this formalism is used to study the influence of CT image noise on measurement precision in the case where the unknown parameters are densities. It is shown that, (1) the unavoidable overlap in the spectral data obtained by the two crystal technique results in a much lower signal‐to‐noise ratio than can be obtained by using the two kV technique, (2) the necessity for hard filtration of the high energy beam in the two kV technique has not heretofore been appreciated, and (3) the dose for a given x‐ray tube heat load is also lower with the two kV technique.

ISSN:0094-2405    

DOI:10.1118/1.594520

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A method of experimentally obtaining both neutron and gamma‐ray spectra in a scattering medium is described. The method utilizes a liquid‐organic scintillator (NE‐213) coupled with a pulse‐shape discrimination circuit. This allows the separation of the neutron‐induced pulse‐height data from the gamma‐ray pulse‐height data. Using mathematical unfolding techniques, the two sets of pulse‐height data were transformed to obtain the neutron and gamma‐ray energy spectra. A small spherical detector was designed and constructed to reduce the errors incurred by attempting spectral measurements in a scattering medium. Demonstration of the utility of the system to obtain the neutron and gamma‐ray spectra in a scattering medium was performed by characterizing the neutron and gamma‐ray spectra at various sites about a 3.7‐μg (1.5 cm active length) californium‐252 source in a tissue‐equivalent medium.

ISSN:0094-2405    

DOI:10.1118/1.594521

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The energy spectra of neutrons produced by 35 and 46 MeV protons, 16 and 28 MeV deuterons, and 44 MeV3He ions on thick beryllium were measured at angles of 0°, 15°, and 45° with respect to the incident beams. The spectra were measured by the time‐of‐flight method for neutrons from the maximum energy down to 1 MeV. Neutron dose rates obtained from the zero‐degree spectra by use of available tissue kerma factors agree with TE–TE ionization chamber measurements.

ISSN:0094-2405    

DOI:10.1118/1.594532

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A calibration monitor has been designed for measuring the constancy of linear accelerator or cobalt unit output between full calibrations. This monitor is battery‐operated, light‐weight, and slides into the shadow tray attachment on a linear accelerator or cobalt unit for easy setup. It provides a digital readout of the dose delivered, and a consistency check can be made in less than two minutes. The precision of the monitor, determined by cobalt‐60 irradiations over a 2 1/2 month period, is±0.6% (standard deviation). The monitor also retains the dose reading in a CMOS digital counter indefinitely, hence it can be used in the same fashion as mailed thermoluminescent dosimeters (TLD) for calibration checks at remote facilities without the complicated readout procedures associated with TLD. The monitor can be mailed to a remote facility, positioned without ambiguity, and irradiated; and the reading can be verified on return to the originating center simply by pressing a switch. The monitor can easily be set up to carry out a ’'blind” check in which the reading obtained is not known to the remote facility.

ISSN:0094-2405    

DOI:10.1118/1.594533

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The detection limitations inherent in statistically limited computed tomographic (CT) images are described through the application of signal detection theory. The detectability of large‐area, low‐contrast objects is shown to be chiefly dependent upon the low‐frequency content of the noise power spectral density. For projection data containing uncorrelated noise, the resulting ramplike, low‐frequency behavior of the noise power spectrum of CT reconstructions may be conveniently characterized by the number of noise‐equivalent x‐ray quanta (NEQ) detected in the projection measurements. The NEQ for a given image may be determined either from a measurement of the noise power spectrum or from the noise granularity computed with an appropriate weighting function. A measure of the efficiency of scanner dose utilization is proposed which compares the average dose to that required by an ideal scanner to obtain the same NEQ.

ISSN:0094-2405    

DOI:10.1118/1.594534

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

ISSN:0094-2405    

DOI:10.1118/1.594535

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY