ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1984.tb36211.x

出版商:Wiley    

年代:1998

数据来源: WILEY

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1984.tb36212.x

出版商:Wiley    

年代:1998

数据来源: WILEY

摘要:

An x‐ray videoabsorptiometric technique was developed for measurement of bone mineral content (BMC)in vivo. The principle utility of this technique is the precise measurement of commonly fractured bones, such as the femoral neck, that are difficult to measure by other techniques because of repositioning problems. Scanning slits reduce scattered radiation and improve linearity of measurements. Heavily filtered, high‐kVp beams are used to minimize errors from beam hardening, and data renormalization is employed to compensate for spatial nonuniformities of the beam and detector. Linearity of measured BMC over the range 0.8 to 5 g/cm2is very good (r=0.998) and compares well to single‐ and dual‐photon absorptiometry. A 1.6% change in measured BMC is observed for a 10% change (∼2 cm) in tissue thickness while a 10% change in marrow type causes a 0.6%–0.8% change in BMC. Manual repositioning of a femur phantom revealed a variation of 0.84% over ten measurements when femur values were referenced to standards. A computer repositioning algorithm provides much easier identification of the region for analysis and yields comparable variation (0.9%).

ISSN:0269-3127    

DOI:10.1118/1.595554

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In this paper, a pseudonoise (PN) coded ultrasonic holographic imaging system design is studied with computer simulation. A system utilizing PN coded phase‐modulated ultrasonic signals is capable of yielding both high lateral and high range resolution. It is found that the time for data acquisition and image reconstruction is much less than that required for some comparable methods. The PN coded imaging system also has excellent noise immunity, and this is of great practical importance. Some results for a simulated three‐dimensional imaging geometry are shown to demonstrate the characteristics of PN coded ultrasound systems.

ISSN:0269-3127    

DOI:10.1118/1.595555

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

For monoenergetic x rays, the detective quantum efficiency (DQE) of an x‐ray image intensifier (XRII) obtained by measuring the ratio of signal to root‐mean‐square (rms) noise is compared with the DQE obtained by the scintillation spectrum method. To obtain agreement between the two methods, the rms noise must be measured at a very low frequency because of the temporal responseRXRII(f) of the XRII. This takes a long time and the measurement of the DQE from the scintillation spectrum is much quicker. Measurement ofRXRII(f) shows that it is dependent on x‐ray flux rate.RXRII(f) measured at the same flux rate as DQE permits correction of DQE measurements to zero frequency. In order to estimate DQE for polyenergetic beams, we need to know as a function of energy not only the DQE but the amount of energy deposited per absorbed x ray. The latter is also obtained from the rms measurement.

ISSN:0269-3127    

DOI:10.1118/1.595556

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

We have designed, constructed, and tested a 95‐channel prototype xenon ionization detector for use in scanned projection radiography (SPR). This detector has higher spatial resolution, is more dose efficient, and is easier to construct than computed tomography (CT) xenon ionization detectors. It consists of two parallel plates separated by a 2‐mm gap filled with xenon gas at 2 MPa (20 atm). One plate is a high‐voltage electrode while the other is a circuit board etched to form an array of metal collector strips focused on the x‐ray source. The resulting detector channels are 0.5 mm wide and 6 cm long. In this paper we present results from measurements of system noise and detector channel calibration. We compared the detector system to a screen/film system and found that it allows the detection of structures with 0.17% radiographic contrast compared to 2% contrast required for detection with screen/film when tested by imaging a 10‐cm‐thick Lucite phantom with a 10×10−6C/kg exposure. From images of resolution test patterns, the limiting resolution of the detector is 2.0 1p/mm at 1.6 magnification. Images of reduction mammoplasty tissue samples, obtained with 1/17 the exposure of screen/film images, had the same low‐contrast sensitivity but contained less high‐contrast detail than the film images.

ISSN:0269-3127    

DOI:10.1118/1.595621

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

In a companion paper, we reported on the construction and testing of a xenon gas ionization detector for use in line scanned projection radiography. Experimental results indicate that the detector has sufficient resolution for chest radiography, but higher resolution is required for mammography. Theoretical analysis suggested that a detector pressurized with Freon 13B1 would have better resolution and higher x‐ray energy efficiency than a xenon‐filled detector for energies below 60 keV. In this paper we compared, theoretically and experimentally, Freon 13B1 to xenon as the detector gas. For a 120‐kVp x‐ray spectrum, the detector filled with 2.0 MPa of xenon had less channel‐to‐channel crosstalk, a higher quantum efficiency (QE), and twice the output signal than the detector filled with 1.4 MPa of Freon (highest possible pressure at room temperature), while for a 60‐kVp spectrum, crosstalk is the same, but the detector has slightly higher QE and 1.4 times the energy efficiency when filled with Freon instead of xenon. We conclude that xenon is better for high‐kVp imaging, while Freon at a lower pressure is slightly better for low‐kVp imaging.

ISSN:0269-3127    

DOI:10.1118/1.595622

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A method for the selection of average stopping‐power(L̄/ρ)airmedand energy‐ absorption coefficient(μ̄en/ρ)airmedratios has been developed. The quality of the x‐ray beam is characterized by the ratio of ionization chamber readings at depths of 20 and 10 cm in water(TMR)1020. For convenience, a relationship is established between experimental(TMR)1020and the nominal accelerating potential (MV) of the accelerator. Experimental(TMR)1020are related to(L̄/ρ)airmedand(μ̄en/ρ)airmedin a three‐step process. First, using experimental and theoretical spectra in the range60Co to 45 MV,(TMR)1020were calculated for primary and first‐scatter photons, and a graph of experimental versus calculated(TMR)1020for these same spectra was constructed. Second,(L̄/ρ)airmedand(μ̄en/ρ)airmedwere calculated for a large number of primary spectra [for most of which experimental(TMR)1020were not available] and a graph constructed that related these quantities and(TMR)1020calculated as above for this group of spectra. Third, using the graphs from the preceding steps, graphs relating the calculated(L̄/ρ)airmedand(μ̄en/ρ)airmedwith experimental(TMR)1020were constructed. Data are presented for water, polystyrene, acrylic, graphite, A‐150, C‐552, Bakelite, and nylon for beams with nominal accelerating potentials in the range 2–45 MV.

ISSN:0269-3127    

DOI:10.1118/1.595643

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The use of x‐ray tubes as radiation sources for Compton scatter densitometry (CSD) is evaluated theoretically. Bias correction factors (bcf's) which correct for differential attenuation due to Compton shift and polychromaticity, and differential scattering cross section due to polychromaticity, are defined to facilitate comparison of monochromatic and x‐ray tube CSD devices. Computer modeling indicates that a 100‐kVp x‐ray tube spectrum hardened with 0.64 mm of Pb filtration yields bcf's 0.008 to 0.34% higher than a 70‐keV monochromatic source for various samples of nylon, and human muscle and bone. This difference is insignificant because multiple scatter errors are typically 1000% higher than errors corrected by bcf's. The high equivalent activities of x‐ray tubes (10 to 80 TBq) and their small focal spots (1.0 to 2.0 mm) allow the long‐standing CSD problems of marginal statistical precision, long counting times, and low spatial resolution to be overcome.

ISSN:0269-3127    

DOI:10.1118/1.595557

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A mobile lung densitometer using conventional x‐ray tubes, NaI detectors, and principles of two‐source, two‐detector Compton scattered densitometry, is described. The device is capable of one to two per second density measurements from a 45‐cm3volume with a precision of 5%. The expectedin vivoaccuracy (2%–3%) is determined by using an anthropomorphic phantom with replaceable lung inserts. The unintentional detection of multiple‐scattered x rays results in a small density‐dependent error. This error is predictable and relatively insensitive to differences in surrounding absorbers such as the chest wall. With this device, dynamicin vivodensitometry of the lung in the clinical laboratory and intensive care unit will be possible.

ISSN:0269-3127    

DOI:10.1118/1.595558

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY