摘要:

Camera‐based single photon emission computed tomography (SPECT) provides increased information about the organ scanned by eliminating superpositioned radionuclidic activity in the reconstructed images. Current literature contains little detail regarding the potential of and the technical aspects involved in using this emerging imaging modality. A description of the instrumentation supplements a general, but practical, background for nuclear medicine personnel. Some of the considerations for successfully utilizing a SPECT system are described, along with a discussion of the basis for these procedures. Pitfalls are mentioned and clinical images from our SPECT imaging system are included.

ISSN:0094-2405    

DOI:10.1118/1.595110

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The effects of detection of scattered radiation in x‐ray transmission CT are studied both theoretically and experimentally. It is shown that scatter induces nonlinear errors in the measurement of attenuation values which can lead to cupping, streaks, and CT number inaccuracies. It is shown that scatter effects predominate over beam spectrum hardening effects for large body parts, and that the artifact propensity is a direct function of the scatter‐to‐primary ratio. The presence of scatter induced streaks were demonstrated experimentally on both a third‐ and a fourth‐generation CT scanner using an appropriate water‐equivalent phantom. A simple model with constant scatter background leads to a correction algorithm which was tested on several phantoms and one human pelvis. The algorithm worked well on the smaller phantoms but was less successful for the larger objects. Nevertheless, it still gave substantial improvement in the pelvic scan. We demonstrated that, at least in the pelvis, scatter is a more significant source of error than beam hardening and that improved scatter correction algorithms are needed. The consequences for the quantitative interpretation of CT numbers for clinical diagnoses are discussed.

ISSN:0094-2405    

DOI:10.1118/1.595111

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A three‐source, three‐detector system for the Compton scattering measurement of lung density is described. The average density is measured in a volume of tissue which is similar in shape to a sphere of diameter 4.0 cm. While scattering measurements of lung density are precise, results in phantoms showed that density in normal man is only about 70% of the gravimetric density. This error is considered to be due predominantly to the influence of multiple photon scattering.

ISSN:0094-2405    

DOI:10.1118/1.595112

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The effects of multiple photon scattering and the assumption of infinitesimal beam geometry on the results obtained with a clinical lung densitometer were investigated. In phantom materials, it was possible to account almost completely for the multiple scatter contribution by measurement of transmission for the170Tm source. A theoretical analysis based on a simplified model showed that the influence of finite geometry was small. Measurements in six normal volunteers showed that lung density is a function of the fractional air content of the lung. To relate density to fractional water content of the lung, measurements must be made at a fixed lung volume. The height in the lung at which measurements are made appears to be unimportant. The results of these experiments enable predictions to be made concerning the clinical usefulness of lung density measurements.

ISSN:0094-2405    

DOI:10.1118/1.595113

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The voltage response of ceramic and polyvinylidene fluoride (PVDF) hydrophones was measured in the receive mode for angles of incidence ranging from 0°–90°. The measurements were performed at 2.5, 3.5, 5.0, and 8.0 MHz; these frequencies are typical of those used in medical diagnosis. The results are compared to three theoretical models based on diffraction theory; correlation between the measured response and theoretical models is evident for some PVDF hydrophones but not for others, and not for any ceramic hydrophone. The effective radius, as defined in the AIUM–NEMA standard for diagnostic ultrasound, is calculated and compared to the test criteria established in that standard. All of the ceramic hydrophones and two of the five PVDF hydrophones failed to meet the criteria.

ISSN:0094-2405    

DOI:10.1118/1.595114

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The photon energies which maximize the signal to noise ratio per unit absorbed dose (optimal photon energies) have been calculated for detection of soft tissue masses within adipose tissue 3–15 cm thick. The detection task simulates mammography in women with fatty breasts. Ideal, plain film and calcium tungstate screen–film systems were considered in the analysis. Net photographic density is not incorporated into this model; therefore, the optimal photon energy with respect to the signal to noise ratio per unit absorbed dose may not be the same as the photon energy which results in maximum film density per unit absorbed dose. Therefore, the model has limited applicability to film or screen–film systems. However, it is directly applicable to digital systems where brightness and contrast can be adjusted.

ISSN:0094-2405    

DOI:10.1118/1.595094

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A new technique is described for the determination of the dose in rad to metastatic lesions in the neck following administration of131I for the treatment of thyroid carcinoma. The technique utilizes a high‐energy pinhole collimator mounted on an Anger camera which can be rotated to record lateral and anterior views from known positions relative to the patient. A new algorithm is derived for the determination of lesion location in three dimensions, utilizing the distance of closest approach between back‐projected rays from the two views. In addition, a new derivation is presented for the estimation of ellipsoid volume from two pinhole projections. The method makes use of a computer edge detection program to delineate the projected lesion boundaries. The output is either a mean estimate from one view or a more definitive upper bound derived from both views. The uptake in counts is determined from daily anterior images which are corrected for pinhole efficiency falloff with distance. This uptake is converted into microcuries by use of an in‐air calibration curve. An attenuation correction is applied using the calculated lesion depth and an assumed attenuation coefficient. The dose rate is calculated using standard assumptions and is integrated graphically over the first few days when the rate peaks and by utilizing a single‐decaying‐exponential fit to the data over the remaining days. Illustrative patient data are presented in which doses are calculated for three neck lesions after an administration of 175 mCi of131I. These doses include a lower bound of 2400 rad and estimates of 5300 and 9500 rad.

ISSN:0094-2405    

DOI:10.1118/1.595096

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The necessity for a mathematical model of human heat transfer as an aid in determining the clinical effectiveness of whole‐body hyperthermia technique is brought out. A 45‐compartment lumped parameter model of the human thermal system is developed. The model accounts for changes in metabolism, blood flow, and other physiological mechanisms during hyperthermia. Simulations of the model's projected temperature distributions and responses to six clinical whole‐body techniques are investigated.

ISSN:0094-2405    

DOI:10.1118/1.595115

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The nuclear medicine uses of short‐lived positron emitters, such as15O and11C, rely primarily on the cyclotron production of these radionuclides. This paper presents an alternate approach to production of15O by the use of photonuclear reactions on16O, using bremsstrahlung radiation produced by an electron linear accelerator. Methods are described which produce useable quantities of relatively high specific activity15O (25.1 mCi/4 min at 27.9 Ci/g), using a reboiling H2O target, with an electron linear accelerator having an electron beam energy of 26 MeV and a beam current of 100 μA. Results of this target system are compared to those of a target system developed recently by other investigators.

ISSN:0094-2405    

DOI:10.1118/1.595104

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The power‐law (Batho) equation for inhomogeneity corrections to the dose calculated in a layered medium has been examined to elucidate the implicit approximations made in its derivation and hence to discover its limitations. Relationships based on primary and first scatter dose calculations are established between the Batho correction and the true correction from which several conclusions can be drawn. For dose corrections within water in a two‐layer medium, the Batho method underestimates the correction when the electron density (ρ) of the overlaying inhomogeneity relative to water is less than 1, and overestimates it when this density is greater than 1. The Batho method is excellent for small fields and ρ1. When the power‐law equation is extended to multilayer media, by assuming that the correction factor for each layer multiplies independently, the method gives less accurate results. The largest errors occur inside an inhomogeneity directly underneath a top layer of unit density, since the contribution from such a layer is inherently ignored. All of these conclusions are demonstrated in the paper by experimental measurements. Finally, relationships are shown between the Batho correction and both the correction factor proposed by MacDonaldet al. and the differential scatter air ratio correction.

ISSN:0094-2405    

DOI:10.1118/1.595098

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY