摘要:

A simple two‐dimensional analytic model is evaluated for transmitted cardiac motion in fetal lung. The model treats the latter as being an incompressible viscoelastic medium. The mean radial deformation in an elastic medium is demonstrated to depend on a length parameterl~μ/ρω2, whereμ, ρ, and ωcorespond to elastic shear modulus, mass density, and frequency of cardiac motion, respectively. Digitized M‐mode images are demonstrated as a feasible method to measure such deformationsin vivo. Data for two patients are presented to illustrate the technique.

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1989.tb36306.x

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

An autoradiographic technique incorporating a new imaging system was used to detect pioninduced radioactivity in Plexiglass and the results were compared with aluminium activation and PET imaging. The activity distribution in the region of the pion‐stopping peak was similar in all three cases. Another large signal in the entrance region due to in‐flight interactions [12C(π −, π − π)11C] was detected by autoradiography and by PET but was not reflected in the aluminium activation measurements. This new technique is capable of defining the stopping region in phantoms with a better resolution than PET scanning and is useful as a complementary technique to other methods of pion dosimetry.

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1989.tb36307.x

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

We perform gamma camera imaging to generate data for estimation of internal radiation dose in our radioimmunotherapy candidates. Because of the inability of single photon emission computed tomography (SPECT) to account for patient attenuation variability without serious error, quantitative planar imaging was performed to estimate the radioactive content of normal organs. We undertook the following studies to further validate this method. A realistic fillable human phantom was used to determine the accuracy of I‐131 filled organ estimation. A transmission scan of the unfilled phantom was produced with an I‐131 filled flat flood source. Anterior and posterior planar images of the filled organs were acquired with region of interest determination of the activity in the organ. Correction by the attenuation factor and a camera calibration factor yielded the MBq in the organ. The procedure was also performed in a simple phantom. Three dogs were imaged and sacrificed to validate the techniquein vivo. A high degree of accuracy in estimation of organ radioactive content was found to be present using the phantom and dog models. Use of this method requires further validation but provides a solid basis for estimation of internal radiation dosimetry in radioimmunotherapy planning.

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1989.tb36308.x

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Many problems in physics involve imaging objects with high spatial frequency content in a limited amount of time. The limitation of available experimental data leads to the infamous problem of diffraction limited data which manifests itself by causing ringing in the image. This ringing is due to the interference phenomena in optics and is known as the Gibbs phenomenon in engineering. Present tehniques to cope with this problem include filtering and regularization schemes based on minimum norm or maximum entropy constraints. In this paper, a new technique based on object modeling and estimation is developed to achieve superresolution reconstruction from partial Fourier transform data. The nonlinear parameters of the object model are obtained using the singular value decomposition (SVD)‐based all‐pole model framework, and the linear parameters are determined using a standard least squares estimation method. This technique is capable, in principle, of unlimited resolution and is robust with respect to Gaussian white noise perturbation to the measured data and with respect to systematic modeling errors. Reconstruction results from simulated data and real magnetic resonance data are presented to illustrate the performance of the proposed method.

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1989.tb36309.x

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In circular tomosyntesis obtained from a sufficient number of radiographs with projection directions forming a single cone, object detail at a distance from the plane of interest is blurred according to the zero order Bessel function. The main lobe of this window function defines slice thickness, while its ringing side lobes are undesirable because they permit further outlying structures to “leak” through. Using the orthogonality of Bessel functions, a sampling scheme consistmg of multiple, concentric projection cones was designed to synthesize by a finite FourierBessel series a slice window with superior side lobe suppression. The window that concentrates the most “energy” within a finite slice, and can be realized by a limited number of sampling cones, is the zero order circular prolate spheroidal function. Its application to tomosynthesis of 3 mm thick slices with a characteristic detail size of 0.5 mm, concentrated 95% of the total series expansion to only 3 concentric circular scans, yielding a theoretical suppression of the first side lobe of − 38 dB, to be compared to − 8 dB achieved with the Bessel function. Experimental implementation of this optimal sampling scheme using 3, 8, and 14 projection views, distributed over cones with opening half‐anges of 1.92, 4.39, and 6.88°, respectively, resulted in a side‐lobe attenuation of at least − 20 dB. This attenuation reduced significantly artifacts arising from out‐of‐plane detail of high spatial frequency (e.g., edges) in tomosynthetic images of clinical interest in dentistry.

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1989.tb36310.x

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

An x‐ray fluorescence system which utilizes polarized radiation to measure lead in vivo in human subjects is described. The minimum detection limit is approximately 6.4 ppm wet weight lead in the cortex of the tibia with 4 mm of overlying soft tissue. This appears to be adequate for assessing lead stores in lead‐toxic preschool children. The measurement requires 16.5 min and is associated with an effective equivalent whole body dose to the subject of 2.5 μSv. The system, its calibration and its validation are described herein.

ISSN:0269-3127    

DOI:10.1118/1.596353

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Diagnostic x‐ray spectra (66–103 kV, 1–2 mA) were measured without pinhole collimator or liquid nitrogen cooling by using a siliconp–i–nphotodiode. An x‐ray count rate was low (≊400 photons/s) at distances of 2–3 m away from an x‐ray target, because theilayer of the photodiode was very small (1.5 mm2in area and 75 μm in thickness). The junction reverse current of the photodiode was 50–70 pA at room temperature and energy resolution for 59.5‐keV γ rays was 2.0 keV (full width at half‐maximum), which was limited by the electric noise of a preamplifier. Measured spectra were corrected for detector distortion. The corrected spectra were similar to those determined with a Ge detector. Thei‐layer thickness of the photodiode was an important parameter for the correction. In particular, when the thickness was thin, the fraction of photoelectron escape became large; this fraction was estimated analytically for variousi‐layer thicknesses. The angular dependence of the full‐energy peak efficiency was measured; for the photons whose energies were above 17.8 keV the angular dependence was isotropic except for angles greater than 60° off the photodiode axis. This method is therefore applicable to the measurement of scattered x rays.

ISSN:0269-3127    

DOI:10.1118/1.596354

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

At present, the phase images together with amplitude images are used in nuclear medicine to aid the diagnosis of cardiac regional wall motion abnormalities (RWMA). The phase images represent the spatial distribution of the relative phase of the first harmonic fit of pixel time activity curves, and the amplitude images represent the distribution of the amplitude of the fit. These images contain only part of the information present in the original radionuclide images, and have to be mentally integrated with other known information to obtain a diagnosis. The proposed synthetic Fourier images overcome these deficiencies as their pixel intensity is a function of additional Fourier parameters of pixel time activity curves and of pixel location and are not limited to the first harmonic. But most importantly, their computation is based on “teaching” the computer by examples of previously diagnosed cases. The images offer direct and robust diagnosis which is superior to that derived from separate phase and amplitude images, especially for the detection of mild RWMA.

ISSN:0269-3127    

DOI:10.1118/1.596355

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

We have studied the effect of breast composition on the average whole breast dose, average glandular dose, and image contrast in mammography, using both computational and experimental methods. Three glandular/adipose compositions were considered: 30/70, 50/50, and 70/30 by weight, for both 3‐ and 5‐cm breast thickness. Absorbed dose was found to increase with greater glandular content and this increase is more pronounced for thick breasts and softer beams. For typical screen–film x‐ray beams, the average dose to a highly glandular breast is nearly twice the dose to a highly adipose breast and the average glandular dose about 40% higher. Dose was reduced when higher energy beams were employed. The use of a grid increased the dose by a factor of 2.0 to 2.6. Finally, the measured image contrast decreases with increasing breast glandularity, to a greater extent in small breasts and when low energy beams were employed.

ISSN:0269-3127    

DOI:10.1118/1.596356

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Previous theoretical work and clinical experience with digital acquisition of fluoroscopic images have identified several problems which needed to be solved. These are: image resolution; blurring due to patient motion, combined with long exposure times; and excessive x‐ray quantum mottle levels. We will show that application of pulsed progressive readout (PPR) methods to the TV camera solves these problems. By permitting a high‐intensity x‐ray pulse to be delivered, all motion is stopped and quantum mottle is reduced to acceptable levels. It will be shown that 1024×1024 digital matrices provide adequate resolution and 8‐bit digitization is sufficient to permit the same quality as is used in conventional 100‐mm photofluorography. User acceptance can be made easier by incorporation of existing photofluorographic controls (with which the radiologist is already familiar) to acquire the digital images. It is possible to interface PPR video systems using existing 100‐mm exposure circuits without much modification and the resulting system can be regarded as a digital 100‐mm camera.

ISSN:0269-3127    

DOI:10.1118/1.596357

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY