Historical note on computed tomography.
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History, 20th Century↗
Biomedical subjects
W G Hawkins
Publications and source records attributed to W G Hawkins.
CT volumetrics of primary liver cancers.
A new computer algorithm is described for liver and tumor volume determinations for patients with hepatoma and primary hepatic cholangiocarcinoma. The algorithm is based on global histograms of CT numbers of the liver and primary liver cancers. The algorithm includes computer-assisted definition of the liver boundary in each CT slice. Liver and tumor volumes of 10 patients calculated by the histogram method were compared with volumes obtained from CT slices that were manually contoured by experienced observers. A correlation coefficient of 0.995 was determined for these two methods of volume computations. Mean values of the differences in volumes obtained by the two methods were 6.7 and 8.0% for the liver and tumor, respectively. The computer algorithm was tested on CT scans for an additional 46 patients by highlighting regions corresponding to normal liver and tumor tissues in each CT slice and determined to be accurate by experienced observers. The computer software is being used clinically to assess tumor response in a new treatment program for primary liver cancers that includes radiolabeled antibodies.
Adenoma, Bile Duct↗
Effective atomic numbers for low-energy total photon interactions in human tissues.
A new method is introduced in which the total photon interaction cross sections per electron of human tissues are used to define effective atomic numbers for blood, bone, brain, fat, heart, kidney, liver, lung, muscle, ovary, pancreas, spleen, and water. These effective atomic numbers are equal within 4% from 10 to 200 keV in each soft tissue, whereas for bones of different chemical compositions the variation ranges from 2.86% to 5.03%. This effective atomic number definition is less energy dependent than a previous definition based on the total photon interaction cross section per atom averaged over all elements in the tissue, from which the computed effective atomic numbers varied by as much as 50% (in bone) as a function of photon energy over the energy range from 10 to 200 keV.
Adipose Tissue↗
The effect of intrinsic attenuation correction methods on the stationarity of the 3-D modulation transfer function of SPECT.
The application of stationary restoration techniques to SPECT images assumes that the modulation transfer function (MTF) of the imaging system is shift invariant. It was hypothesized that using intrinsic attenuation correction (i.e., methods which explicitly invert the exponential radon transform) would yield a three-dimensional (3-D) MTF which varies less with position within the transverse slices than the combined conjugate view two-dimensional (2-D) MTF varies with depth. Thus the assumption of shift invariance would become less of an approximation for 3-D post- than for 2-D pre-reconstruction restoration filtering. SPECT acquisitions were obtained from point sources located at various positions in three differently shaped, water-filled phantoms. The data were reconstructed with intrinsic attenuation correction, and 3-D MTFs were calculated. Four different intrinsic attenuation correction methods were compared: (1) exponentially weighted backprojection, (2) a modified exponentially weighted backprojection as described by Tanaka et al. [Phys. Med. Biol. 29, 1489-1500 (1984)], (3) a Fourier domain technique as described by Bellini et al. [IEEE Trans. ASSP 27, 213-218 (1979)], and (4) the circular harmonic transform (CHT) method as described by Hawkins et al. [IEEE Trans. Med. Imag. 7, 135-148 (1988)]. The dependence of the 3-D MTF obtained with these methods, on point source location within an attenuator, and on shape of the attenuator, was studied. These 3-D MTFs were compared to: (1) those MTFs obtained with no attenuation correction, and (2) the depth dependence of the arithmetic mean combined conjugate view 2-D MTFs.(ABSTRACT TRUNCATED AT 250 WORDS)
Humans↗