Leslie M. Zatz

Energy dependent reconstruction in X-ray computerized tomography

Abstract Polychromatic X-ray sources are universally used in computerized tomography to obtain adequate intensity. These sources, however, can produce significant artifacts in the reconstructed image due to non-linearities. Methods are shown for minimizing these artifacts by using compensating non-linearities. In addition systems are described which utilize spectral analysis in the detection system. The detected spectrum is divided into a low and high energy region. The resultant signals are processed to obtain a photoelectric component, which is atomic-number dependent and a Compton scattering component which is density dependent. This information removes the distortion and provides delineation of specific materials.

Computer-interactive Method for Quantifying Cerebrospinal Fluid and Tissue in Brain Ct Scans: Effects of Aging

Presented here is a modification of a previously developed, computed, semiautomated system for quantifying the amount of CSF and tissue on brain CT scans. The technique automatically strips skull from brain and applies a two-dimensional high-pass filter to reduce spectral-shift artifact. The resultant images are presented along with the raw images, section by section, on a screen for fluid-tissue differentiation by a human scorer. This is accomplished by adjusting a one-bit display of the filtered image until a satisfactory separation threshold is found. Data can be summed within or across sections to provide measures of CSF volume in specific regions of interest such as the ventricles and sulci. A major advantage is the improved accuracy of sulcal measurement. This method has been applied to scans of 57 community volunteers, 20–84 years old. High correlations have been established between rankings performed by an experienced clinician and automated rankings (r = 0.88 with rankings based on ventricular size, and r= 0.83 with rankings based on sulcal size). Furthermore, significant correlations were found between computed measures of ventricular size and age and between sulcal widening and age.

White matter changes in cerebral computed tomography related to aging.

Changes on computed cranial tomography related to aging were studied in 123 normal subjects aged 23 to 88 years. The attenuation value of the white matter in the centrum semiovale decreased with age. When the effect of age was excluded, ventricular and sulcal size did not have an independent effect on the attenuation value. This finding suggests that there may be gradual changes in the chemical composition of white matter with aging.

An inaccuracy in computed tomography: the energy dependence of CT values.

The CT values of a variety of materials were studied in an EMI and a Syntex head scanner. The presence of bone-simulating rings changed the CT values despite the use of constant length water paths and software corrections. Errors due to beam hardening in CT scanning are discussed. These errors could be of significance, particularly in quantitative studies. The changes in CT values with KV setting of the scanner are used to illustrate their energy dependence and the peculiarities of the scaling system introduced by EMI. The difficulty in specifying a standard scale or unit for CT scanners is discussed.

Cranial computed tomography in aphasia. Correlation of anatomical lesions with functional deficits.

A variety of aphasic patients were studied to determine the relationship betweeen lesion size, as demonstrated by cranial computed tomography (CCT), and the type of aphasia, as classified by the Boston Diagnostic Aphasia Examination (BDAE). CCT demonstrated a variety of lesions. Those in nonfluent Brocas aphasics and fluent Wernickes aphasics were separable into pre-Rolandic and post-Rolandic areas, respectively. Conduction, global, and anomic aphasics had different lesion sites. Correlation of lesion location by CCT with aphasia type supports Geschwinds concepts of aphasia.

Clinical application of Compton and photo-electric reconstruction in computed tomography: preliminary results.

Although computed tomography has demonstrated some promise in the direction of quantative radiology, valuable information related to the varying response of tissues to x-rays of different energy is still not utilized on a routine basis. Advancements in a method proposed by Alvarez and Macovski for decomposing dual-spectra CT projection data into its material-dependent Compton and photo-electric components are described. Results are presented to demonstrate that such a separation can be performed. Reconstructed images of separated Compton and photo-electric data obtained from clinical scans are shown. With the improvements described, the Compton images begin to approach the quality of conventional reconstructions with evidence of improved polychromatic correction. The photo-electric data, while separable, suffers from unacceptable noise level. Analysis of this difficulty is presented, with recommendations for future improvement by careful selection of the effective energy of the low energy spectrum. The encouraging results suggest that this technique warrants continued development and evaluation.

Semiautomated Methods for Quantitating CSF Volume on Cranial Computed Tomography

Two methods for quantitating cerebrospinal fluid (CSF) volume in each hemicranium and on the total section on cranial computed tomography are described and compared. Both analyses utilize information input by the user, but differ in their treatment of volume averaging. The second analysis (Automated Section Information-I) measured partially volumed CSF more sensitively. Potential inaccuracies due to technical artifacts are summarized.

Neurologic dysfunction in patients treated for small cell carcinoma of the lung: A clinical and radiological study

The neurologic dysfunction in 7 patients treated for small cell carcinoma (SCC) of the lung by combination chemotherapy and prophylactic brain irradiation was evaluated. The disease appeared to be a diffuse encephalopathy frequently affecting the higher cortical functions. Five out of seven patients had progressive dysfunction leading to death in 1 to 26 months; one patient had stabilization of symptoms followed by death in 21 months, probably from the neurologic disease as well as SCC; one patients symptoms improved. The clinical course of the neurologic disorder seemed different from the known reactions to brain irradiation and from the other neurologic syndromes associated with lung cancer. The relative contributions of cranial irradiation and treatment with chemotherapeutic agents in producing the neurotoxicity are not known. Computed tomographic (CT) brain scans done after the onset of symptoms did not show any focal signs or necrosis. However, there was a suggestion of progressive increase in intracranial fluid volume on the scans. The incidence of the disorder, 10.2% among a group of 49 patients, suggests the need for prospective studies to evaluate the problem.

Quantitative CT scan studies in aphasia ☆: I. Infarct size and CT numbers

Abstract Infarct siźe (number of 1-mm 2 pixels in the lesion) on CT scans of 30 aphasia patients was obtained with a semiautomated computer program. The mean number of lesion pixels present per slice containing lesion was approximately 500 for mild aphasias (transcortical motor and conduction), 700 for Wernickes, 1000 for Brocas, 1500 for mixed, and 2000 for globals. These differences were significant for 11 15 of the group pairwise comparisons. When lesion locus was controlled for in the anterior/posterior plane, 73–100% of the aphasia patients were correctly classified as to type of aphasia by a discriminant analysis utilizing only the number of lesion pixels present on two CT slices. Different slice combinations were used for different aphasia group comparisons. There was a significant correlation between severity of aphasia and lesion size. There was a significant correlation between lesion size and the CT numbers in the lesion. This type of analysis may be useful to predict the prognosis for recovery potential in aphasics who have CT scans performed at 2 months poststroke.

The effect of the kVp level on EMI values. Selective imaging of various materials with different kVp settings.

A variety of materials and tissues as well as 3 patients were studied with the EMI scanner using the 100-, 120-, and 140-kVp settings. There was little shift in the EMI value for most tissues over this range, but significant shifts occurred with materials whose effective atomic number was moderately different from that of water. Use of the highest kVp setting may improve visualization of low-contrast images by decreasing the noise caused by statistical fluctuations. This shift in EMI values can be used to determine the approximate amount of material of high atomic number present, such as calcium or iodine.