Reducing radiation exposure from survey CT scans

OBJECTIVE: The purpose of this study was to focus attention on the technique factors commonly used in survey CT scans (e.g., scout, topogram, or pilot scans) to measure the radiation exposure from typical survey CT scans, to compare their exposure to that of typical chest radiographs, and to explore methods for radiation exposure reduction. MATERIALS AND METHODS: The default survey CT scans on 21 CT scanners, representing three different vendors and 11 different models, were investigated. Exposure measurements were obtained with an ion chamber at isocenter and adjusted to be consistent with standard chest radiographic exposure measurement methods (single posterior-anterior projection). These entrance exposures were compared with those of typical chest radiographs, for which the mean for average-sized adults is 16 mR (4.1 x 10(-6) C/kg). RESULTS: The entrance exposures of the default survey CT scans ranged from 3.2 to 74.7 mR (0.8 to 19.3 x 10(-6) C/kg), which is equivalent to approximately 0.2 to 4.7 chest radiographs. By changing the default scan parameters from 120 kVp to 80 kVp and the tube position from 0 degrees (tube above table) to 180 degrees (tube below table), the entrance exposure for the survey CT scan was reduced to less than that of one chest radiograph for all CT scanners. CONCLUSION: For institutions at which the interpreting radiologists do not rely heavily on the appearance of the survey CT image, we recommend adjusting the technique parameters (kilovoltage and X-ray tube position) to decrease radiation exposure, especially for vulnerable patient populations such as children and young women.     

Generation of three dimensional images from CT scans: technological perspective

Routine production of three dimensional (3-D) surface images from CT scans for clinical applications has been performed in 700 cases. These images have been found useful in craniofacial, orthopedic, and neurosurgical applications. Three dimensional images may be produced on the same CT scanner that collected the original slices. The emergence of 3-D imaging as a routine radiological procedure involves special technological requirements to avoid artifacts and to produce a useful result. Three dimensional surface reconstruction procedures are reviewed and examples of clinical application are presented.     

Evaluation of calcium concentration in bones from CT scans

Fresh cadaveric lumbar vertebrae from 28 subjects were obtained at autopsies and then analyzed by CT scans. An average CT number, calibrated against water and representing the relative x-ray attenuation coefficient of cancellous bone of each vertebra, was obtained. Calcium concentrations in milligrams per cubic centimeter for each vertebral specimen, calculated by physical methods, were plotted against the average CT numbers. The results suggest a linear relationship between the CT numbers and the calcium content of bone.     

Atypical CT scans in adrenoleukodystrophy

Computed tomography has become a valuable tool in the diagnosis of adrenoleukodystrophy because of a characteristic CT pattern of symmetrical low density areas in the parietooccipital region often with a peripheral rim of enhancement. However, a few cases have been reported that depart from this classic pattern. We have recently observed an atypical CT pattern where instead of diminished attenuation in the white matter, extensive calcifications were seen with a symmetric distribution in the parietooccipital regions. There was no associated contrast enhancement.     

Interobserver discrepancies in distance measurements from lumbar spine CT scans

Lumbar spine computed tomographic (CT) scans of 10 patients were examined independently at two levels by five experienced radiologists. At each level the minimum midline sagittal diameter was measured, and at each intervertebral space the left foramen was measured for its minimum diameter. Statistically significant differences were found between the measurements of different observers, differences that in a number of cases could have led to disagreement over whether or not stenosis was present. There were reasonably strong correlations between different observers' readings of midline sagittal diameters but generally not of foraminal diameters. Reasons for discrepancies between observers in spine CT measurements are reviewed briefly.     

Patients undergoing recurrent CT scans: assessing the magnitude

To assess percent of patients undergoing multiple CT exams that leads to cumulative effective dose (CED) of ≥ 100 mSv and determine their age distribution. Data was retrieved retrospectively from established radiation dose monitoring systems by setting the threshold value of 100 mSv at four institutions covering 324 hospitals. The number of patients with CED ≥ 100 mSv only from recurrent CT exams during a feasible time period between 1 and 5 years was identified. Age and gender distribution of these patients were assessed to identify the magnitude of patients in the relatively lower age group of ≤ 50 years. Of the 2.5 million (2,504,585) patients who underwent 4.8 million (4,819,661) CT exams during the period of between 1 and 5 years, a total of 33,407 (1.33%) patients received a CED of ≥ 100 mSv with an overall median CED of 130.3 mSv and maximum of 1185 mSv. Although the vast majority (72–86%) of patients are > 50 years of age, nearly 20% (13.4 to 28%) are ≤ 50 years. The minimum time to accrue 100 mSv was a single day at all four institutions, an unreported finding to date. We are in an unprecedented era, where patients undergoing multiple CT exams and receiving CED ≥ 100 mSv are not uncommon. While underscoring the need for imaging appropriateness, the consideration of the number and percent of patients with high exposures and related clinical necessities creates an urgent need for the industry to develop CT scanners and protocols with sub-mSv radiation dose, a goal that has been lingering. • We are in an era where patients undergoing multiple CT exams during a short span of 1 to 5 years are not uncommon and a sizable fraction among them are below 50 years of age. • This leads to cumulative radiation dose to individual patients at which radiation effects are of real concern. • There is an urgent need for the industry to develop CT scanners with sub-mSv radiation dose, a goal that has been lingering.     

Morphomic calcification score from clinical CT scans: A proxy for coronary artery calcium

BackgroundScreening of cardiovascular risk is essential in preventing cardiac events and quantifying asymptomatic risk. Coronary artery calcium (CAC) scores are a well-established in predicting cardiovascular risk, but require specialized computed tomography (CT) scans. Given the relationship of aortic calcification with cardiovascular risk, we sought to determine whether aortic calcification measures from incidental CT scans may approximate CAC.Study designRetrospective CT scans and corresponding volumetric CAC scores were obtained from patients at the University of Michigan. Aortic calcifications were measured in 166 scans. Correlations between a novel morphomic calcium (MC) percent score and CAC score were evaluated using Kendall's correlation coefficients. Comparison of receiver operating characteristic (ROC) curves based on MC at different vertebral levels showed the highest predictive values for measures taken at L4.ResultsMC at L4 shows promise in predicting CAC (AUC 0.90 in non-contrast scans, 0.70 in post-contrast scans). Proposed MC threshold are (4.21% for best sensitivity, B 12.93% for balance, C = 19.26% for specificity) in scans without contrast enhancement and (D = 7.31 for sensitivity, E 8.06 for specificity) in scans with contrast enhancement.ConclusionThe MC score demonstrates promising potential in approximating CAC, particularly at the L4 level. The utilization of MC from incidental CT scans may be useful for assessment of cardiovascular risk. The ability to extract MC from contrast scans makes it especially valuable to patients receiving additional medical or surgical care. Recognition of high-risk patients would allow the use of indicated preventative strategies to avoid hard cardiovascular events in at risk patients.     

Appropriateness of out-of-hours CT head scans

This study was conducted to evaluate the appropriateness of the out-of-hours computed tomography (CT) head scans (scans performed outside normal working hours) in a large district general hospital in the United Kingdom. CT scan request forms and CT reports of adult patients were reviewed who had their CT head scans done between 1700 and 0900 h the next day and all weekend and national holidays in the study period of 4 months. Information regarding change in the patient management resulting from CT scan was extracted from review of patients’ case notes. An urgent CT head scan request was deemed appropriate if it led to an immediate change in a patient’s management. Appropriateness of the requests according to the various guidelines was also evaluated. One hundred and twenty-one patients were included in the study. Majority (70%) of the scans were requested by the emergency department. Eighty-one (66%) scans were both requested and performed between 1700 and 2200 h. Immediate change in management of 80% patients occurred. In 20 (17%), the change in management occurred only after 0900 h the next day and in 4 (3%), management did not change at all. Common scenarios involving change in patient’s management included intracranial bleed requiring urgent neurosurgical intervention and hemorrhagic stroke being ruled out. Out-of-hours CT head scans also facilitated early discharge of the patients with head injuries and headache from the hospital. This retrospective study has found that a high proportion of out-of-hours CT head scans were appropriate and led to change in the patient’s immediate medical care. An Editor’s comment on this paper is available at and a reply to the comment is available at .     

Rapid three-dimensional display of the cerebral ventricles from noncontrast CT scans

Three-dimensional images of the cerebral ventricles may now be generated from routine serial axial or coronol noncontrast CT scans in 5-8 min and rotated in space interactively in 2-5-s to provide the physician with useful views of anatomic relationships difficult to depict in other ways.     

Ocular volume measured by CT scans

Summary Newer CT scans have greatly enhanced oculometric research and made it possible to measure ocular dimensions. With these measurements, ocular volume can be more accurately estimated to understand its relationship with age and sex. One hundred CT orbit scans with presumed normal eyes were used for the data base. The mean values and normal variations of ocular volumes at various ages in both sexes are presented. Rapid growth of the eyeball was noted during the first 24 months of age. It reached its peak between the ages of 18 and 30 years of age, after which there was a reduction. Results may be of help in recognizing eye abnormalities such as microophthalmus and macrophthalmia.     

Serial CT scans in thymic hyperplasia

A case of thymic hyperplasia in juvenile myasthenia gravis presenting as interval thymic enlargement on serial CT scans is described. The CT scans correlated with clinical worsening.     

Three-dimensional surface reconstruction of the carpal bones from CT scans: transaxial versus coronal technique

Computer methods for reconstruction of three-dimensional (3-D) images from standard CT scans have been developed. The process does not require special computer knowledge and can be performed with a unmodified CT scanner. 3-D images are especially valuable for conveying information to nonradiologist physicians, who are unfamiliar with the numerous slice-format images produced in a standard CT examination. The utility of these methods for clarification of areas of complex skeletal anatomy has been previously demonstrated in the literature. We performed 3-D imaging on a normal isolated cadaver hand and on a patient with scaphoid fracture. In both cases the 3-D images obtained had excellent osseous anatomical detail. A method of acquisition of high quality wrist CT scans, suitable for 3-D processing, is suggested.     

Gold storage in the liver: appearance on CT scans

The authors present one case in which high attenuation values in the liver parenchyma on computed tomographic scans were found in a patient who had been previously treated with colloidal gold for rheumatoid arthritis. Reticuloendothelial storage of gold was proved by biopsy.     

Artifacts on lung CT scans: removal with Fourier filtration

A preliminary study was done of Fourier analysis of high-resolution computed tomographic (CT) images of normal pulmonary parenchyma. A two-dimensional fast Fourier transform was applied to 20 regions of interest (64 x 64 pixels) obtained from CT images of six lungs. A qualitative analysis of the spectra and the application of filters in the frequency domain allowed the characterization and removal of reconstruction artifacts. Selective application of a low-pass filter removed these parasitic frequencies and clearly enhanced the quality of the image.     

Pulmonary lymphangitic spread of carcinoma: appearance on CT scans

Chest computed tomography (CT), including high-resolution CT with thin (1.5-mm) sections was used to evaluate proved (pathologically or clinically) lymphangitic spread (LS) of tumor in 12 patients. These appearances were compared with thin-section scans obtained in 11 healthy subjects. Thin-section CT demonstrated findings consistent with thickening of the normal lung interstitium. In all patients, thin sections showed an increase in the number of peripheral lines (1-2 cm in length) that were diffuse in generalized disease and localized in focal disease. Normal peripheral arcades were not increased in number, but the limbs forming the arcades were thickened in all patients. A diffuse increase in linear and curvilinear structures (reticular pattern) was seen toward the center of the lung. Polygonal structures 1-2 cm in diameter were seen in seven patients with LS but not in healthy subjects. Fissures were thickened in nine patients. Selected 1.5-mm-thick CT sections are recommended through abnormal areas (seen at CT or on chest radiographs) or if these are normal at three levels (midapex, hilus, and 3 cm above the diaphragm) when scanning patients with tumors known to cause LS.     

Determination of liver volume from CT scans using histogram cluster analysis.

The histogram cluster analysis procedure (HICAP), which was developed by NASA for processing satellite images, classifies images into discrete clusters of pixels according to one or more arbitrary imaging variables. We incorporated this nonparametric, multivariate procedure in a semiautomatic computer algorithm for calculating total liver volume from CT scans and compared its performance with that of a human observer. Total liver volumes were calculated from CT scans in adult patients by the algorithm and by an experienced radiologist using the trackball controlled cursor at the CT console. Variability in the computer calculated volumes was determined by repeating calculations three times over the course of 3-12 months. Using HICAP in the univariate mode, we calculated total liver volumes from 28 contrast enhanced CT scans in 27 patients. Liver volumes calculated by the semiautomatic and manual methods had a median absolute difference of 3.6% (Vcomputer = 1.08 * Vmanual - 99.52 cc; r2 = 0.99). Median day-to-day variability of the computer calculated volumes was 1.9% (95% confidence interval: 1.3-2.7%). Using HICAP in a bivariate mode to illustrate its ability to incorporate two image features in one analysis, we studied an additional patient and compared total liver volume calculated from the univariate data set defined by the contrast enhanced CT scan with that calculated from the bivariate data set defined by nonenhanced and contrast enhanced CT scans. The HICAP errors were 4.1% in the univariate analysis and 0.4% in the bivariate analysis. It is concluded that this statistical clustering algorithm provides a clinically accurate, repeatable, and feasible method of in vivo liver volume determination.     

Automated scene analysis of CT scans.

Since the advent of computed tomography, there has been an increasing realization that CT scans contain quantitative as well as qualitative information useful in the diagnostic process. Often however, the use of this information is impeded by the tedious manual outlining of the areas of interest in the scan. To alleviate this problem, we have developed a scene segmentation algorithm which will automatically delineate areas of interest in a CT scan. This procedure uses known information about the expected objects in the scan in conjuction with an algorithm to label those objects. The resultant scene segmentation divides the scan into four anatomical areas: skull, normal brain, high density lesions and CSF. After an area of interest is interactively selected by the clinician, volume, density or other quantitative measures may be computed. Limitations of the algorithm and its clinical applications are discussed.