Comments on 'The noise power spectrum of CT images'.
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Tomography, X-Ray Computed↗
Biomedical subjects
K Faulkner
Publications and source records attributed to K Faulkner.
Radiation dose to patient and staff during percutaneous nephrostolithotomy.
The radiation dose to the patient and to members of staff was monitored during 18 procedures for the percutaneous removal of renal stones. It was found that the radiation dose to the patient was minimal and was about the same as for an IVU. The overall dose to the staff was acceptably low and within safety limits. It was concluded that PCNL is a safe procedure from the radiation point of view but it may be advisable to take certain precautions if the workload is high.
Fluoroscopy↗
Contrast-detail assessment of computed tomography scanners.
The design and construction of contrast-detail detectability phantoms for the assessment of the imaging performance of CT scanners are described. These phantoms have been employed to undertake a series of measurements on a number of different machines. The results are expressed in terms of object contrast which is consistent with the conventional definition of radiological contrast. For one particular scanner, the imaging performance of a number of image reconstruction and post-processing filters has been investigated. The results indicate that there was no observed energy dependence of contrast-detail detectability once differences in technique factors and attenuation were taken into account. A similar conclusion was drawn from the results of a set of measurements made to examine the effect on detectability of additional filtration.
Evaluation Studies as Topic↗
A detailed study of radiation dose and radiographic technique during chest radiography.
The radiation dose to a series of patients referred for chest radiography has been monitored using thermoluminescent dosimetry. The postero-anterior projection was employed throughout the study. Measurements were made in two rooms of the same general hospital. Each room was equipped with automatic exposure control of the air ionisation chamber type. The effect of this equipment on patient exposure was investigated and compared with manual exposure control. In all cases the tube potential (kVp) was selected by the radiographer but tube current (mA) was determined by the generator. Anterior and posterior radiation doses were measured using sachets of lithium fluoride. For each group of patients the anterior exit dose, and therefore all of the radiation dose, was lower when automatic control was used. The standard deviation on the anterior patient dose was lower under automatic control, which resulted in fewer films needing to be repeated due to incorrect film density. Film densities were also investigated using a densitometer, to provide a further comparison between the two types of exposure control.
Adult↗
Radiation doses and somatic risk to patients during cardiac radiological procedures.
The radiation dose to a series of adult and paediatric patients undergoing cardiac catheterisations and adults having percutaneous transluminal coronary angioplasty has been measured/determined directly using lithium fluoride thermoluminescent dosemeters and indirectly using an air ionisation chamber which indicated exposure-area product. Somatic and genetic risks are estimated from the dosimetry results. It is suggested that the magnitude of the radiation hazard is negligible compared with other clinical hazards associated with these procedures.
Adult↗
Radiation dose received by patients during barium meal investigations under automatic brightness control.
The radiation dose to a group of patients undergoing double-contrast barium meal investigations was monitored using lithium fluoride thermoluminescent dosemeters (TLD). All examinations were performed by the same radiologist in two rooms at the same hospital. Both rooms contained equipment with an undercouch tube/overcouch image intensifier configuration. The examinations were performed at a pre-selected tube potential using automatic brightness control which varied the screening current to keep the dose rate at the image intensifier input surface constant. It may be deduced from the results that there is a significant difference in mean radiation dose between the two rooms. These measurements were used to estimate the radiation dose to other organs, such as the testes, ovaries, uterus and active bone marrow.
Barium Sulfate↗
An investigation of the radiation dose to staff during cardiac radiological studies.
Measurements of radiation distributions in the vicinity of the couch were undertaken for a number of projections commonly employed during cardiac radiological studies. Three types of investigations were considered; cardiac catheterisations, pacemaker implants and percutaneous transluminal coronary angioplasties. The radiation dose to staff involved in these procedures was estimated. For each group of staff, the maximum annual workload and the workload which would necessitate an individual becoming a classified radiation worker may be deduced from an expression given in the text.
Anesthesiology↗
Analysis of x-ray computed tomography images using the noise power spectrum and autocorrelation function.
A discrete representation of the reconstruction process, consistent with the method of data collection, has been used to derive expressions for the noise power spectrum, autocorrelation function and noise equivalent quanta (NEQ) of a computed tomography (CT) image. These parameters have been expressed in terms of basic scanning factors such as tube current, exposure time, slice width and number of detectors. Each of these factors affects the overall magnitude of the noise power spectrum, but the spatial frequency dependence is also determined by the type of reconstruction filter used in the computer algorithm. The noise power spectrum has been calculated for scanners employing either a ramp or Hanning weighted ramp filter. Predictions made from this theoretical analysis have been compared with experimental measurements made on various CT scanners. Measurements were made of the modulation transfer function (MTF) by techniques which permitted us to deduce the contributions of the algorithmic and non-algorithmic components to the overall MTF. NEQ values have been calculated for a number of CT scanners.
Humans↗
Noise and contrast detection in computed tomography images.
A discrete representation of the reconstruction process is used in an analysis of noise in computed tomography (CT) images. This model is consistent with the method of data collection in actual machines. An expression is derived which predicts the variance on the measured linear attenuation coefficient of a single pixel in an image. The dependence of the variance on various CT scanner design parameters such as pixel size, slice width, scan time, number of detectors, etc., is then described. The variation of noise with sampling area is theoretically explained. These predictions are in good agreement with a set of experimental measurements made on a range of CT scanners. The equivalent sampling aperture of the CT process is determined and the effect of the reconstruction filter on the variance of the linear attenuation coefficient is also noted, in particular, the choice and its consequences for reconstructed images and noise behaviour. The theory has been extended to include contrast detail behaviour, and these predictions compare favourably with experimental measurements. The theory predicts that image smoothing will have little effect on the contrast-detail detectability behaviour of reconstructed images.
Humans↗
An alignment ruler for computed tomography scanning.
This patient alignment ruler has been developed to deduce the position of high resolution CT scans relative to an anatomical marker. In addition, the ruler may be used to check the accuracy of the scan plane indicator lights and the consistency of the couch incrementation on any CT scanner. The ruler has been specifically designed for use with scanners employing a 13 mm slice width; however, it may easily be modified for other widths, by altering the hole pattern. An alignment device has been described in a previous publication (Nettle 1979) in which calculations using measurements made on the TV monitor were necessary. However, the ruler described here requires only visual interpretation. This ruler is both inexpensive and easy to manufacture.
Humans↗
Scattered radiation distributions around computed tomography scanners and the associated radiation hazard to personnel.
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Humans↗
An assessment of the radiation dose received by staff using fluoroscopic equipment.
Measurements of scattered radiation were made on two fluoroscopic installations, one with an overcouch tube and one with an undercouch tube. The annual doses to staff involved in a fluoroscopic procedure undertaken on both types of unit were estimated using measured dose rates and weighting factors referred to in ICRP 26. Environmental monitoring at the protective barrier was performed for various room layouts to determine the effect of both equipment and room design on the annual dose received by staff at the control panel. In all circumstances the annual dose to staff inside the control cubicle was negligible.
Environmental Exposure↗
The impact of afterloading machines in the treatment of gynaecological cancer.
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Brachytherapy↗
Haemoglobin, smoking and peripheral vascular disease.
One hundred and four patients with peripheral vascular disease requiring operation were reviewed retrospectively with respect to age, sex, preoperative haemoglobin, smoking habits and diabetic status. The preoperative haemoglobin levels and smoking status in 63 non-diabetic male patients with peripheral vascular disease were compared with a matched group of individuals treated for inguinal hernia. For all patients there was a significant correlation between smoking habits, preoperative haemoglobin level and the presence of peripheral vascular disease. The mechanisms by which smoking may damage the vascular tree are reviewed.
Age Factors↗
Asynchronous replication of heterochromatin in maize.
Replication patterns of four classes of heterochromatin in the chromosomes of maize were analyzed. Centromeric heterochromatin, distal heterochromatin of the B chromosomes, and knob heterochromatin all have asynchronous late replication, knob heterochromatin being the last chromosomal DNA to complete replication. Nucleolus organizer heterochromatin replicates during the period of euchromatin DNA replication. The proportion of the S period involved in asynchronous late replication is directly dependent on the amount of heterochromatin in the nucleus. Both additional knob and B-chromosome heterochromatin participate in this effect. Each additional B chromosome produces an increment in the proportion of nuclei with asynchronous replication; in nuclei with 12 B chromosomes, the proportion of the S phase showing asynchronous late replication is more than 3 times greater than that in nuclei without B chromosomes. The data are consistent with the hypothesis that delayed DNA replication of knob heterochromatin is responsible, in some genotypes, for the loss of chromosome segments and for B-chromosome nondisjunction in the second pollen grain mitosis.
Journal Article↗
Age differences in false recognition using a forced choice paradigm.
Recent findings suggest that older adults may be more susceptible to false recognition responses than younger adults because of age differences in gist-based processing at both encoding and retrieval. It has been suggested that age differences in the quality of memory representations that result from this age-related reliance on gist processing can produce age differences in response criteria, with older adults employing more lenient criteria than young adults. Support for this argument comes from studies where suppressed false recognition in older adults occurs with shifts toward more conservative response criteria. The current study further examined this issue by minimizing the effects of response criteria by using a two alternative forced-choice task in the study of false recognition in young and older adults. This manipulation reduced false recognition in both young and older adults, but did not eliminate age differences in false recognition.
Adult↗
Angiotensin-converting enzyme inhibitor resets baroreceptor reflexes in conscious dogs.
The present experiments investigate whether the absence of tachycardia during lowering of blood pressure (BP) with an angiotensin-converting enzyme inhibitor (CEI) in salt-depleted dogs is due to an alteration in the activity of the baroreflex. Baroreflex activity was measured after pharmacological manipulation of BP using intravenous nitroglycerin or phenylephrine, and the heart period (R-R interval) relative to the arterial pressure pulse was recorded. The slope of the relationship between BP and R-R interval is a measure of the sensitivity of the baroreceptor reflex and displacement of the line indicates a change in the setpoint of BP. On normal sodium diet, the sensitivity and setpoint of the baroreflex were unaltered by the nonapeptide CEI given both intravenously and into a lateral cerebral ventricle. During salt depletion. however, intravenously but not centrally administered CEI altered the setpoint of the baroreflex without modifying the sensitivity. The alteration in the setpoint that occurred following intravenous CEI in the salt-depleted dog could well account for the fact that the fall in BP induced by CEI does not cause reflex tachycardia. These results indicate that circulating but not brain angiotensin II is essential for the maintenance of baroreflex function during sodium depletion and provide further evidence for the important interactions between angiotensin and the autonomic nervous system.
Angiotensin-Converting Enzyme Inhibitors↗
Second malignant tumors after childhood cancer.
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Child↗