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At least 19 recordsLinked to original sources
PubMed1978

Polychromatic streak artifacts in computed tomography images.

A series of artifacts in computed tomography (CT) images, consisting of streaks coming off edges and flares surrounding the object being scanned, is shown to be due to polychromaticity of the X-ray beam. These artifacts are seldom seen on conventional CT brain scans. They are helpful in understanding artifacts such as those seen around the petrous bone of the skull. Following this, a comparison is made between "single energy" and "dual energy" correction schemes for poly-artifacts. The theoretical assumptions underlying either method are analyzed, and the importance of these concepts in dual energy reconstructions is stressed. A new test phantom is suggested to evaluate different poly-correction schemes. All the simulated projection data in this study are noise free and are reconstructed using an industrial convolution-back projection technique. In addition, reconstructions are shown of the phantom using real data taken with and without a water bag path length compensator.

Mathematics↗
PubMed1979

Nonlinear polychromatic and noise artifacts in x-ray computed tomography images.

The variance of the image noise in computed X-ray transmission tomography (CT) due to quantum noise is in a first approximation a nonlinear function of X-ray attenuation. Beam hardening in CT is also a nonlinear function of attenuation. We present a theoretical study of both phenomena. Computer simulations and numerical results show that both nonlinear dependencies have quite similar effects on image quality. We also show how the two-dimensional distribution of the noise variance in a CT image is a weighted superposition of images obtained by backprojecting integer powers of the noiseless projection data corresponding to the scanned object. The streak-like pattern in the image noise due to the anisotropic nature of the noise cross-correlation function is discussed. We also discuss how these nonlinear phenomena affect noise filtering and tissue characterization using statistical parameters.

Electronics, Medical↗
PubMed1979

[Single photon radioisotope emission computed tomography image using gamma camera (author's transl)].

Single photon radioisotope computed tomography (RCT) images were obtained using the following devices such as conventional gamma camera, data processer for exclusive use of nuclear medicine (C.D.S.-4096), magnetic tape and medium size electronic computer FACOM 230-28S (48K) for multipurposes, which are routinely used for clinical purpose. To reconstruct the RCT image we made absorption correction by geometric mean of opposing counts considering the thickness of source and used the convolution integral method. The reconstructed images of phantom study resolved one centimeter clearly and were very similar to original. The RCT image of patient was acquired by the rotation of patients using the revolving chair and the handmade implement which settles the center of patient's head. Three dimensional informations were obtained by one examination with a gamma camera which collects two dimensional images. When using a gamma camera, therefore, not only a transaxial but an arbitraly RCT image will be important to contribute for diagnosis.

Brain Neoplasms↗
PubMed1978

General purpose digital display system for computed tomography images.

The authors describe a microprocessor-based digital image display system utilizing a solid-state image memory with a high quality television-type monitor for display of computed tomography images. It is an alternative to a commercially available display system, and offers the potential for research in digital image display. It is now under clinical evaluation. Image input to the stand-alone display system is via 9-track magnetic tape common to almost all CT machines, and it may be programmed to accept digital tapes from any type of CT machine and display them in a common format.

Data Display↗
PubMed1979

Optimal processing of computed tomography images using experimentally measured noise properties.

The spatial resolution and noise properties of a computed tomography (CT) image may be altered by two-dimensional linear filtering of the initial image. In this paper, we derive filters that minimize the noise variance subject to a constraint on the spatial resolution. The resulting filter functions can reduce the noise variance by 17% in comparison with conventional filters. The method for obtaining these filters requires knowledge of the noise and imaging properties of the system. We derive theoretical expressions for these properties and introduce experimental techniques for their measurement. The statistical characteristics are shown to be anisotropic, spatially variant, and object dependent. We discuss the implications of this result both for optimal filtering and for the general problem of CT image noise property measurement.

Humans↗
PubMed1977

Radionuclide imaging, computed tomography, and gray-scale ultrasonography of the liver: a comparative study.

Transmission computed tomography (CT), gray-scale ultrasonography, and scinitillation-camera imaging were compared for detection of intrahepatic space-occupying processes. Fifty patients with suspected liver disease were studied by the three modalities. In the 35 cases with confirmed abnormalities, the madalities were rated on a scale of 0 to 5 in terms of their detection value; Each modality was found to have definite advantages and disadvantages. The mean score of ultrasound was highest (3.61), followed by nuclear medicine (3.11) and then CT (2.77). The combination of ultrasound and nuclear medicine identified all lesions, whereas CT alone or in combination with another technique occasionally failed to detect abnormal foci. In the future, the relative efficacy of these procedures may change with improved imaging technology and increased interpreter experience.

Carcinoma, Hepatocellular↗
PubMed1978

Image quality in cranial computed tomography.

Image quality in cranial computed tomography (CT) was evaluated with phantom and patient studies on both a first (single beam) and a second (multiple beam) generation scanner. When comparable radiation doses were used, there were only minor differences in resolution, low contrast detectability, and noise level. The pattern of noise relative to the size of the area in which it was measured was somewhat different. On patient studies, no differences were found when contrast-material-filled vessel visibility and gray--white matter distinction were analyzed. A lesion was obscured by streak artifacts in one scanner in one of 22 patients scanned on both machines. The major factor in image quality as seen in the two scanners seemed to be in the production of artifacts. This was apparent in artifacts from motion, high contrast discontinuities, beam hardening, and edge enhancement. Multiple factors must be considered in assessing CT image quality. In particular, further studies to quantitatively evaluate noise quality and artifact production are needed.

Brain↗
PubMed1978

Standardization of computed tomography images by means of a material-selective beam hardening correction.

Polychromaticity of the X-rays used in computed tomography (CT) has made it difficult to establish an absolute scale for CT values and has made quantitative comparisons between patients unreliable. The spectral shift of the X-rays depends on the material distribution within the structure measured and is significant if substantial amounts of bone, fat, or injected contrast material are present. A material-selective beam hardening correction procedure has been developed that allows the reconstruction of good approximations of linear attenuation coefficients with respect to a reference energy. With the aid of mathematical simulations and measurements on a physical phantom, the feasibility of the procedure and its insensitivity with regard to energy settings and other machine parameters are documented.

Humans↗
PubMed1977

Nuclide imaging and computed tomography in cerebral vascular disease.

This report presents our experience with computed tomographic and radionuclide scans in 224 patients with ischemic or hemorrhagic infarcts or intracerebral hematomas secondary to cerebral occlusive vascular diseases. The results vary according to the site of vascular occlusion. The radionuclide angiograms and static scintigrams show four distinct patterns in cases of occlusion of the middle cerebral artery. Computed tomographic scans exhibit less variation in appearance and have a higher sensitivity in cases of recent ischemic infarction. The "tentorial confluence sign" is an important finding on static scintigrams in patients with occipital infarction; if this sign is not present, this diagnosis should be suspect. Earlier reports have established the value of computed tomography and radionuclide scans in the evaluation of cerebral infarction. In individual cases, however, each of these modalities may render nondiagnostic or false negative findings; combining both both types of examinations and comparing results yield a greater likelihood of an accurate diagnosis of cerebrovascular disease. Computed tomography is clearly more valuable than radionuclide scans in the diagnosis and follow-up of hemorrhagic infarcts or parenchymal hematomas.

Aged↗
PubMed1979

Computer tomography, radionuclide imaging and ultrasonography in hepatic mass lesions.

The livers of 86 patients comprising this report were examined by both transmission computerized tomography (CT) and radionuclide scans (LS). Fifty-nine of them were also examined by gray-scale ultrasound (US). In a comparative study, the strengths and weaknesses of each modality were evaluated. CT demonstrated 85%. US 82%, and LS 73% of masses involving the liver. Because of better resolution and sectioning capabilities, together with stop-motion imaging, CT and US detected smaller and deeper mass lesions than did LS. However, LS was more informative in hepatocellular disorders than was US or CT. Our experience indicated that information obtained on the liver and surrounding structures by each imaging modality used here tends to be somewhat unique, and thus these procedures complement one another rather than being competitive.

Humans↗
PubMed1978

The complementary role of gallium citrate imaging and computed tomography in the evaluation of suspected abdominal infection.

Fifteen patients with a suspected abdominal abscess were examined by both gallium-67 and computed tomographic scanning. The Ga-67 scan was a useful screening examination, correctly identifying all eight cases of infection, whereas the CT scan missed one case of a pericecal phlegmon. Misdiagnosis of infection by Ga-67 scan occurred in 2/8 cases without infection but the CT scan correctly identified all noninfected patients. While this series is too small to decide whether there is significant difference in the ability of the two procedures to suggest the correct diagnosis, it is felt that Ga-67 and subsequent CT scans may be complementary in that a Ga-67 scan can initially locate the abnormality and thus direct the CT scan, which can confirm the diagnosis or avoid a misinterpretation of the Ga-67 scan. Computed tomography also provides more anatomical detail, better location of the lesion, and demonsrates lesions noninfectious in nature.

Abdomen↗
PubMed1978

Computed tomography and radionuclide imaging of the liver: a comparative evaluation.

The authors retrospectively analyzed the results of radionuclide imaging (RI) and computed tomography (CT) of the liver in 174 patients. RI correctly identified 90% of patients with focal hepatic lesions while CT identified 85%. CT was capable of differentiating tumor, abscess/hematoma, and cyst while RI was more sensitive in the detection of hepatocellular disease. CT distinguished regenerating nodules from other focal lesions. Radionuclide imaging remains the preferred initial screening examination in patients with suspected focal liver disease, while CT is the examination of choice to distinguish obstructive from nonobstructive jaundice.

Diagnostic Errors↗
PubMed1979

Computed tomography: a three-dimensional study of the nasal airway.

1. Accurate volume measurement of the nasal airway based upon computed tomography images sequentially generated along the length of the airway is possible. 2. The cross-sectional area of the airway at any position along its length can be determined. 3. The most constricted part of the airway is not necessarily at the location of the turbinates. 4. Details of hard- and soft-tissue anatomy not otherwise discernible can be detected with computed tomography imaging.

Cephalometry↗
PubMed1975

Relative efficacy of radionuclide imaging and computed tomography of the brain.

Computed tomography (CT) with the EMI scanner has been demonstrated to possess a wide spectrum of capabilities in the diagnosis of suspected intracranial disease. This review of 418 dual CT and radionuclide (RN) brain images indicates that RN and CT are complementary in the diagnosis of cerebral infarction, but that CT has a greater capability in brain tumor detection. The classical RN static brain image does not detect cerebral atrophy, hydrocephalus or intraventricular hemorrhage; these conditions are clearly defined by CT.

Acute Disease↗