Showing papers in "Journal of Computer Assisted Tomography in 1981"
TL;DR: The effect of neuroanatomical structure size, shape, and position versus spatial tomographic resolution on quantitation in positron computed tomography was investigated and recommendations for error reduction and possible correction factors are provided.
Abstract: :The effect of neuroanatomical structure size, shape, and position versus spatial tomographic resolution on quantitation in positron computed tomography was investigated. For neuroanatomical structures, voxel sizes in excess of 3 ml exceeded the volume of most structures examined. When the v
340 citations
TL;DR: A head-positioning device allowing accurate position transference between computed tomography and positron emission tomography is described, and the coordinates of an anatomic structure may be determined and transferred between the two images.
Abstract: A head-positioning device allowing accurate position transference between computed tomography and positron emission tomography is described. A base plate is fixed to the patient's head through either an individual mold or screws into the calvarium. This base plate fits onto the headholders of the two devices, thus ensuring that scans are taken at the same level. Using the regular software, the coordinates of an anatomic structure may be determined and transferred between the two images.
318 citations
TL;DR: The quantitative initial single-pass clearance of the agent in the brain suggests its use in evaluation of regional brain perfusion and its interaction with brain amine-binding sites suggests its possible application in studies of cerebral amine metabolism.
250 citations
TL;DR: The additional statistical noise produced in images by subtraction of ACs from total coincidence data demonstrates the advisability of minimizing AC rates in spite of an ability to adequately measure and compensate for their presence in the data.
Abstract: Accidental coincidences (ACs) and methods of compensation for ACs were investigated in terms of their effect on quantitation in positron emission computed tomography (ECT). Formulations of basic expressions describing the physical factors, which cause true coincidences or ACs, are presented to provide a framework of contrasting the two phenomena. Correction of image data for attenuation of the annihilation radiation or nonuniformities in detector efficiency is shown to amplify errors caused by the presence of ACs in the data. It was shown that failure to compensate for ACs caused overestimates in measurements of isotope concentrations from image data and that in many cases the overestimate was significant for relatively modest percentages of ACs in the data. Three methods of compensation for ACs were evaluated as to their accuracy and effect on statistical noise in images. It was found that nonuniform detector efficiencies could cause prominent image artifacts if an inadequate method was employed in the determination and subtraction of ACs from image data. The additional statistical noise produced in images by subtraction of ACs from total coincidence data demonstrates the advisability of minimizing AC rates in spite of an ability to adequately measure and compensate for their presence in the data.
228 citations
TL;DR: Three sources of harmful health effects from nuclear magnetic resonance (NMR) in vivo techniques have been examined and a practical upper level for absorbed power is 4 W/kg in medically important studies of short duration (less than 10 min).
Abstract: Three sources of harmful health effects from nuclear magnetic resonance (NMR) in vivo techniques have been examined with the following conclusions: (a) Static magnetic fields. Harmful effects on humans and reproducible cellular, biochemical, or genetic effects have not yet been observed at fields less than 2 Tesla (20,000 gauss). (b) Changing magnetic fields. The threshold for effects of induced currents is above that produced from less than 1 to 100 Hz sinusoidal field changes with a maximum field of 5 mT (50 gauss). Waveform, repetition rate maximum B field, and duration of exposure are parameter requiring further study. (c) Radiofrequency (RF) heating. A practical upper level for absorbed power is 4 W/kg in medically important studies of short duration (less than 10 min). For long-term studies, 1.5 W/kg is a reasonable level in low humidity environments. The power absorbed by the subject can be estimated by measuring the RF coil Q before and after the subject is placed in the NMR instrument. Large metal objects will absorb power in proportion to the conductivity of the device or prosthesis.
209 citations
TL;DR: This method for estimating the average dose from a CT procedure has been evaluated as a function of the number of scans in the multiple scan procedure and location in the dosimetry phantom using single scan dose profiles obtained from five different types of CT systems.
Abstract: A method for describing the absorbed dose delivered by x-ray transmission computed tomography (CT) is proposed which provides a means to characterize the doses resulting from CT procedures consisting of a series of adjacent scans. The dose descriptor chosen is the average dose at several locations in the imaged volume of the central scan of the series. It is shown that this average dose, as defined, for locations in the central scan of the series can be obtained from the integral of the dose profile perpendicular to the scan plane at these same locations for a single scan. This method for estimating the average dose from a CT procedure has been evaluated as a function of the number of scans in the multiple scan procedure and location in the dosimetry phantom using single scan dose profiles obtained from five different types of CT systems. For the higher dose regions in the phantoms, the multiple scan dose descriptor derived from the single scan dose profiles overestimates the multiple scan average dose by no more than 10%, provided the procedure consists of at least eight scans.
192 citations
Journal Article•
TL;DR: In this article, a nuclear magnetic resonance (NMR) machine capable of producing tomographic sections of the whole human body in vivo has been constructed based on a four coil, air-core electromagnet producing a field of 0.04 T which corresponds to a proton NMR frequency of 1.7 MHz.
Abstract: A nuclear magnetic resonance (NMR) machine capable of producing tomographic sections of the whole human body in vivo has been constructed. This system is based on a four coil, air-core electromagnet producing a field of 0.04 T which corresponds to a proton NMR frequency of 1.7 MHz. The images are produced line by line using a selective excitation technique. Magnetic field gradients up to about 5 mT/m are employed. Electronic subsystems are described here including a radiofrequency (RF) amplitude feedback circuit, an RF power amplifier, a transmit/receive switch, a receiver pre-amplifier and gradient coil drivers. For a single scan through a 103 mm3 sample of human muscle tissue in vivo, the measured proton density uncertainty is 24% and the spin-lattice relaxation time (T1) uncertainty is 74%. Phantom images using CuSO4 solution and in vivo sections through human chest, thighs and head are presented. T1 measurements of human muscle, liver and brain tissue in vivo give results which agree well with T1 values for corresponding rabbit tissues measured in vitro.
153 citations
TL;DR: This paper examines the influence of certain assumptions in the underlying steady-state model of cerebral blood flow and oxygen utilisation using continuous inhalation of C15O2 and 15O2 to estimate the quantities in grey and white matter.
Abstract: There is a growing interest in the tomographic measurement of regional cerebral blood flow and oxygen utilisation using continuous inhalation of C15O2 and 15O2 This paper examines the influence of certain assumptions in the underlying steady-state model Estimations are made for possible errors in the actual measurement of these quantities in grey and white matter
149 citations
TL;DR: A technique has been developed to measure regional values of vascular and extravascular lung density using positron emission and transmission tomography and a pronounced anteroposterior gradient of both lung density and blood density was observed, while the gradient of extrav vascular lung density was quite small.
Abstract: A technique has been developed to measure regional values of vascular and extravascular lung density using positron emission and transmission tomography. Quantitative values of lung density in a transaxial plane are obtained by recording transmission scans during the exposure of a ring source of positron emitting germanium/gallium-68, which encircles the subject in the plane of the scan. Values of blood density are obtained by scanning in the emission mode following the labeling of the subject's red blood cells with a quantity of C-carbon monoxide inhaled as a bolus. Subtraction of the normalised blood volume scan from the normalised lung density (transmission) scan provides regional values of extravascular lung density. The response of the transmission scan to changes in density was obtained by scanning different tissue equivalent materials in the density range 0.02 to 1.0 g cm-3. This resulted in a linear relationship between pixel counts and density. Density measurements made in vitro on simulated chest phantoms suggest that, at worst, random errors of 3.5% and systematic errors (due to the influence of the chest wall) of between 10 and 15% will be incurred when measurements are made in vivo on lungs of average normal density (0.3 g cm-3). The random error associated with the emission scan (arising from counting statistics alone) was found to be 1.2%. Measurements of lung density made on five normal subjects (supine) resulted in a mean density of 0.29 g cm-3 for a region in the lower (caudal) part of the lung, with a range of values between 0.26 and 0.32 g cm-3 from subject to subject. A pronounced anteroposterior gradient of both lung density and blood density was observed, while the gradient of extravascular lung density was quite small. The mean value of the ratio extravascular: vascular lung density for both caudal and cranial lung regions was 0.92 +/- 0.25.
126 citations
TL;DR: In this article, a TOF-assisted PET device is proposed to estimate the difference between the time of flight (TOF) of the annihilation photons between their inception and their detection.
Abstract: In positron emission tomography (PET), the annihilation radiation is usually detected as a coincidence occurrence that localizes the position of the annihilation event to a straight line joining the detectors. The measure of the difference between the time of flight (TOF) of the annihilation photons between their inception and their detection permits the localization of the position of the annihilation event along the coincidence line. The incorporation of TOF information into the PET reconstruction process improves the signal-to-noise ratio in the image obtained. The utilization of scintillation detectors utilizing cesium fluoride scintillators, fast photomultiplier tubes, and fast timing circuits allows sub-nanosecond coincidence timing resolution needed for the effective use of TOF in PET. Mathematical considerations and pilot experiments show that with state-of-the-art electronic components and through the application of proper reconstruction algorithms, the combination of TOF and PET positional data improves severalfold the signal-to-noise ratio with respect to conventional PET image reconstruction at the cost of increasing the amount of data to be processed. The construction of a TOF-assisted PET device is within the capability of state-of-the-art technology.
122 citations
TL;DR: In this paper, a convolution-back projection reconstruction algorithm is used to obtain estimates of the two-dimensional distribution of acoustic speed and attenuation within the scanned planes of the breast, which are associated with cancer.
Abstract: Transmission ultrasound computer-assisted tomography has been developed for detection and diagnosis of cancer in the breast. Pulses of ultrasound (8 MHz ±3 MHz) are transmitted through the breast in a coronal plane from a plurality of directions. The received signal is processed for arrival time and for changes in amplitude. The measured values for arrival time and attenuation are used in a convolution-back projection reconstruction algorithm to obtain estimates of the two-dimensional distribution of acoustic speed and attenuation within the scanned planes of the breast. Over 1000 images in breasts of approximately 150 patients have been scanned of whom 30 had biopsy proven cancer. Some common characteristics of the reconstructed images which are associated with cancer are 1) increased speed relative to the embedding tissue associated with 2) decreased attenuation in central region of the lesion usually with 3) a ring of higher attenuation at the border of the lesion. Current estimates of sensitivity and specificity of this system for cancer are approaching those of X-ray mammography techniques.
TL;DR: The system is under clinical use for cerebral blood flow studies using 133Xe inhalation or 8lmKr intracarotid continuous infusion, and for blood-brain barrier studies using 99mTeO4 or 68Ga-EDTA, and has yielded many fruitful results.
Abstract: A hybrid emission tomograph, combining a single photon emission tomograph (SET) and a positron emission tomograph (PET) in one system, has been developed. The system was designed as a high speed, high accuracy neurological tomograph capable of measuring cerebral blood flow with 133Xe, cerebral glucose metabolism with 18F-fluorodeoxyglucose, etc. The detector array consists of 64 Nal crystals in a 42 cm diameter circle. Two collimator sets can slide axially on the inner face of the crystal ring to change from SET to PET imaging. The SET collimator consists of 64 units, each containing a 2 mm thick, 30 × 70 mm tungsten fin plus five sub-fins. All the fins are driven synchronously to swing back and forth over a 60° angle, covering an image field of 21 cm diameter. Linear sampling is selectable from 2.5 to 20 mm by changing the ring rotation increments. Slice thickness is also selectable with interchangeable slice collimators of 16, 20, and 24 mm gap. SET performance with 99mTc showed a resolution of 7.5 and 10 mm full width at half maximum (FWHM) at the periphery and at the center, respectively. System sensitivity with the 20 mm slice collimator is 10,000 counts/sec/μCi/ml for a 20 cm diameter uniform solution of 133Xe and 21,000 counts/sec/μCi/ml for 99mTc. The fastest scan time is 2 sec and provides a spatial resolution of 20 mm FWHM, which is sufficient for dynamic studies of 133Xe clearance. The PET collimator consists of two doughnut shaped lead plates that define the slice plane. The gap is selectable at 12, 20, and 28 mm. Linear sampling in PET is about 20 mm with a stationary ring, 10 mm employing the ring rotation, and 3 mm with the ring wobble. The wobble diameter is 7.3 mm. The PET resolution with a S8Ga line source and a nine point wobble is 11 mm FWHM at the center and 13 mm at a 10 cm radius. System sensitivities were 7,000, 20,000, and 30,000 true events per μCi/ml for 12, 20, and 28 mm slice gap, respectively. Presently, the system is under clinical use for cerebral blood flow studies using 133Xe inhalation or 8lmKr intracarotid continuous infusion, and for blood-brain barrier studies using 99mTeO4 or 68Ga-EDTA, and has yielded many fruitful results.
Journal Article•
TL;DR: A new method was developed whereby close comparisons can be made between components of a computed tomography (CT) image and neuropathological findings, which applied in seven cases of malignant supratentorial astrocytic gliomas and in one case of thalamic ependymoma.
Abstract: A new method was developed whereby close comparisons can be made between components of a computed tomography (CT) image and neuropathological findings. This was achieved by a combination of intravital (terminal) CT, postmortem CT, and whole brain sectioning of formalin-fixed tissue. The method was applied in seven cases of malignant supratentorial astrocytic gliomas (Kernohan Grades III and IV) and in one case of thalamic ependymoma. The glioblastoma-like parts of the astrocytic gliomas were usually correctly delineated by postcontrast CT, although there were exceptions to this rule. Tumor components consisting of diffusely growing malignant astrocytoma were difficult or impossible to delineate by CT. Necrotic areas within the tumors were accurately outlined by postcontrast CT. Peritumoral edema was correctly delineated by CT, but growth of diffuse astrocytoma or the presence of astrocytic gliosis within this edematous area seems difficult or impossible to evaluate by current CT techniques.
TL;DR: The method takes into account attenuation of gamma rays inside the source and makes use of an iterative technique, based on the difference between the projection data obtained from the sources and computed projections, called reprojections, from successive reconstructions of the sources.
Abstract: A method of computing tomographic images from single photon radionuclide emission data is presented. The method takes into account attenuation of gamma rays inside the source and makes use of an iterative technique, based on the difference between the projection data obtained from the source and computed projections, called reprojections, from successive reconstructions of the sources. The method has been tested both by computer simulations and reconstruction of plastic phantoms imaged with 99mTc radionuclides. Substantial improvement in reconstruction accuracy over algorithms uncorrected for internal attenuation is demonstrated. Since the technique is iterative, it can be used with a variety of reconstruction algorithms or combined with other first approximation techniques of attenuation correction.
TL;DR: The volume of the dog's liver, kidneys, and spleen were measured by computed tomography (CT) and a water displacement method and individual measurements were reproducible to within ±3%.
Abstract: The volume of the dog's liver, kidneys, and spleen were measured by computed tomography (CT) and a water displacement method. Organ volume determination by CT is a rapid, simple procedure that is accurate to +/- 5% of the organ volume measured by water displacement. Individual measurements were reproducible to within +/- 3%. Determination of organ volume has potential importance in a variety of clinical situations.
TL;DR: Twenty-two patients with mass or destructive lesions at different levels of the spine underwent closed needle biopsy guided by computed tomography (CT), and 18 of the specimens obtained were sufficient for a histologic diagnosis.
Abstract: Twenty-two patients with mass or destructive lesions at different levels of the spine underwent closed needle biopsy guided by computed tomography (CT). Eighteen of the 22 specimens obtained were sufficient for a histologic diagnosis. In one, normal bone tissue obtained was not consistent with the clinical and radiographic picture, resulting in a false negative diagnosis. Except for one patient who developed transient quadriparesis that resolved spontaneously within 2 days, no bleeding complications or neurologic deficits attributable to the procedure were noted. Closed needle biopsy of spinal lesions under CT guidance is advocated as a safe and convenient technique for all levels of the spine. Modifications of the needle used and more experience will be necessary to increase the yield of positive results.
TL;DR: CT is an accurate method of detecting and staging recurrent rectal carcinoma and for aiding the selection of appropriate therapy in patients who underwent CT of the pelvis and abdomen following surgery for adenocarcinoma of the rectum.
Abstract: We studied a series of 39 patients who underwent computed tomog-raphy (CT) of the pelvis and abdomen following surgery for adenocarcinoma of the rectum. Based on the CT findings. recurrent rectal carcinoma was classi-fied into one of four stages: Stage I, intraluminal mass without colon wall
TL;DR: Back-projected images of a simplified chest phantom, 42 cm in diameter and filled with relative activity concentrations of 1.0, 5, and 5, are presented for the unfiltered data to demonstrate the improvement in image quality obtained with the use of TOF.
Abstract: A feasibility study was carried out to determine whether image quality can be improved by the use of time-of-flight (TOF) information in positron emission tomography (PET). The experiment used two fast cesium fluoride detectors followed by constant-fraction discriminators for coincidence-timing resolutions of 600 to 800 psec full width at half maximum, depending on the energy discrimination level. A point source was scanned to study the spatial response of the point spread function with and without the TOF information for nonfiltered back-projected data. Back-projected images of a simplified chest phantom, 42 cm in diameter and filled with relative activity concentrations of 1.0, and 5, are presented for the unfiltered data to demonstrate the improvement in image quality obtained with the use of TOF. Filtered and reconstructed images of this phantom are also presented to show the relative differences in the images obtained with PET and TOF-PET techniques for similar filter functions.
TL;DR: Thirteen patients with pericardial abnormalities and a question of constrictive hemodynamics underwent contrast enhanced cardiac computed tomography (CT) and defined sites of particular constriction for subsequent resection.
Abstract: Thirteen patients with pericardial abnormalities and a question of constrictive hemodynamics underwent contrast enhanced cardiac computed tomography (CT). Those with clinical and catheterization evidence of restricted cardiac filling demonstrated three CT signs: a dilated IVC, a deformed ventricular contour, and an angulated interventricular septum. Patients with pericardial fluid, thickening, or calcification but without evidence of constriction showed none of these signs. Cardiac CT also defined sites of particular constriction for subsequent resection.
TL;DR: A series of axial transverse proton nuclear magnetic resonance scans through the heart are presented that demonstrate clear delineation of both the wall and cavity of the constituent chambers.
Abstract: :A series of axial transverse proton nuclear magnetic resonance scans through the heart are presented that demonstrate clear delineation of both the wall and cavity of the constituent chambers. The anatomical substrate of the sections is explained, and the potential applications of these pre
TL;DR: While all but one subject tolerated xenon inhalation without ill effects, that individual did experience unpleasantly severe dysesthesias and a brief period of unresponsiveness.
Abstract: Short- and long-term side effects during and after inhalation of premixed xenon oxygen (28-47%) from 12 studies are reported. While all but one subject tolerated xenon inhalation without ill effects, that individual did experience unpleasantly severe dysesthesias and a brief period of unresponsiveness. We believe that further human studies with xenon inhalation should be conducted to explore possible early indicators for reduced tolerance of xenon by certain individuals.
TL;DR: Results obtained so far indicate that intervals of 3 months are adequate for following the natural course of osteoporosis or its response to therapy on an individual basis.
Abstract: Computed tomography (CT) has the potential of providing a precise quantification of trabecular bone. A special purpose low dose CT system for applications at peripheral measuring sites has been developed. With this system, the quantification of trabecular bone can be achieved with a reproduc
TL;DR: A computer software system for automatic outlining of borders between regions of differing CT numbers on computed tomography scans has been developed, and results are given along with histograms of the enclosed regions, demonstrating several further applications of these techniques.
Abstract: A computer software system for automatic outlining of borders between regions of differing CT numbers on computed tomography scans has been developed. The technique was originally intended for application in defining inhomogeneities for radiation therapy treatment planning; however, several other applications are possible. The system scans an image using a simple threshold model to locate initial outline points and then completes the outline with a border-following algorithm. Results of the automatic outlining system are given along with histograms of the enclosed regions, demonstrating several further applications of these techniques.
TL;DR: Preliminary results from six multilevel ventilation studies in dogs demonstrate that the lung may be repeatedly imaged during reproducible phases of respiration even when interscan table incrementation is employed to survey a number of tissue segments and breathing is permitted between scans.
Abstract: New developments in computed tomographic technology permit rapid, serial images that may yield information concerning tracer kinetics through a large tissue volume. One possible application of these developments is the derivation of local lung ventilation by observing the temporal changes of stable xenon concentrations. Preliminary results from six multilevel ventilation studies in dogs demonstrate that the lung may be repeatedly imaged during reproducible phases of respiration even when interscan table incrementation is employed to survey a number of tissue segments and breathing is permitted between scans. In addition, subanesthetic xenon concentrations provide adequate enhancement for possible quantification.
TL;DR: Four cases of cerebral emboli diagnosed on computed tomography as foci of increased density are discussed, where the emboli were calcified in at least two cases and seen to lodge at typical scan sites.
Abstract: Four cases of cerebral emboli diagnosed on computed tomography as foci of increased density are discussed. The emboli were calcified in at least two cases. Both cardiac and carotid sources contributed dense emboli, which were seen to lodge at typical scan sites: near the anterior cerebral artery bifurcation (two cases) and in the middle cerebral artery horizontal segment-trifurcation region (two cases).
TL;DR: Differential diagnosis between dementia and depression may be better aided by studying the CT numbers rather than the presence of prominent sulci, which are higher for six nondementia cases than for 14 dementia cases.
Abstract: Patients in their 50s who show clinical signs of dementia (possible Alzheimer's disease) often have ocmputerized tomographic (CT) scans that appear normal. This study examined the mean CT number within a 169-pixel sample in white matter in the centrum semiovale slice. Slice sizes ranged from 6,800 to 9,000 pixels; all were without contrast enhancement. The CT numbers were higher for six nondementia cases (CT numbers of 41 and above)than for 14 dementia cases (CT numbers of 40 and below). The non-overlap in mean CT numbers between the two groups was observed independent of the presence or absence of prominent sulci. Similar low CT numbers were observed for seven patients with senile dementia. Differential diagnosis between dementia and depression may be better aided by studying the CT numbers rather than the presence of prominent sulci.
TL;DR: These studies demonstrated increasing glucose metabolic rates in the human primary (PVC) and associative visual cortex as the complexity of visual scenes increased, indicating the wide range and metabolic reserve of the visual cortex.
Abstract: These studies demonstrated increasing glucose metabolic rates in the human primary (PVC) and associative (AVC) visual cortex as the complexity of visual scenes increased. The metabolic response of the AVC increased more rapidly with scene complexity than that of the PVC, indicating the greater involvement of the higher order AVC for complex visual interpretations. Increases in local metabolic activity by as much as a factor of 2 above that of control subjects with eyes closed indicate the wide range and metabolic reserve of the visual cortex.
TL;DR: The results indicate that constant attenuation can be compensated for by using an attenuation-dependent filter that reconstructs the transverse section reliably and Computer time requirements are two times that of conventional TCT or positron ECT and there is no increase in memory requirements.
Abstract: A back projection of filtered projection (BKFIL) reconstruction algorithm is presented that is applicable to single-photon emission computed tomography (ECT) in the presence of a constant attenuating medium such as the brain. The filters used in transmission computed tomography (TCT)-comprised of a ramp multiplied by window functions?are modified so that the single-photon ECT filter is a function of the constant attenuation coefficient. The filters give good reconstruction results with sufficient angular and lateral sampling. With continuous samples the BKFIL algorithm has a point spread function that is the Hankel transform of the window function. The resolution and statistical properties of the filters are demonstrated by various simulations which assume an ideal detector response. Statistical formulas for the reconstructed image show that the square of the percent-root-mean-square (percent-rms) uncertainty of the reconstruction is inversely proportional to the total measured counts. The results indicate that constant attenuation can be compensated for by using an attenuation-dependent filter that reconstructs the transverse section reliably. Computer time requirements are two times that of conventional TCT or positron ECT and there is no increase in memory requirements.