Beam Computed Tomography Research Articles

An optimized computed tomography protocol for metallic gunshot head trauma in a seal model.

Computed tomography (CT) is commonly used to assess animals with head trauma. However, strongly attenuating objects such as metallic gunshot cause artifacts that may make accurate localization of shrapnel pieces difficult. The purpose of this study was to develop an optimized CT protocol for minimizing metal artifacts in an animal model of gunshot head trauma. A cadaver head of a stranded Gray seal (Halichoerus grypus) was shot post-mortem with a 0.223-inch caliber rifle. The head was frozen, thawed, and scanned using a multislice CT scanner and protocols with varying acquisition and reconstruction parameters. Scans were acquired with and without use of the scanner's proprietary Extended CT Scale (ECTS) mode and beam hardening reduction (Posterior Fossa Optimization [PFO]) filter. Window/level display settings were also varied. For each protocol and each of five selected metallic shrapnel pieces, a single observer measured combined metal halo artifact and shrapnel area using a hand-traced region of interest. The number of hypo- and hyper-attenuating streak artifacts was also recorded. Measurements were repeated for three different reading sessions. Metal CT artifacts were minimized with a high-frequency image reconstruction algorithm and a wide window setting. Further artifact reduction was achieved with a proprietary ECTS raw data reconstruction technique and a very wide window. This enabled a more confident evaluation of surrounding bone. On the other hand, these techniques are unfortunately not effective under conditions of soft tissue evaluation. Increasing tube voltage and use of a proprietary PFO filter did not yield a significant reduction in metal artifacts.

Fan/cone beam CT: visualisation and applications for non-clinical X-ray imaging

Computed tomography (CT) for non-clinical applications is constantly evolving in many different fields, from industry, laboratory and metrology applications. The Technological Center AIMEN, in collaboration with the University of Santiago de Compostela, has implemented a dual-detector computed tomography system. A specific visualisation tool has been developed including 3D rendering and image reconstruction, following the modular capabilities of the CT system. Software capabilities include CT reconstruction for different geometries, special filtering, higher computer memory requirements, basic knowledge extraction, etc., resulting in flexible software with possibilities for further applications development. This new tool is adapted to the emerging needs of an open CT system which is built in a modular configuration to answer new challenges, as those for dimensional metrology (improving its spatial resolution and image quality) and specific analysis for non-destructive testing.

Cone Beam Computertomography (CBCT) in Interventional Chest Medicine - High Feasibility for Endobronchial Realtime Navigation

Introduction: Currently there are several advanced guiding techniques for pathoanatomical diagnosis of incidental solitary pulmonary nodules (iSPN): Electromagnetic navigation (EMN) with or without endobronchial ultrasound (EBUS) with miniprobe, transthoracic ultrasound (TTUS) for needle approach to the pleural wall and adjacent lung and computed tomography (CT) -guidance for (seldom if ever used) endobronchial or (common) transthoracical approach. In several situations one technique is not enough for efficient diagnosis, therefore we investigated a new diagnostic technique of endobronchial guided biopsies by a Cone Beam Computertomography (CBCT) called DynaCT (SIEMENS AG Forchheim, Germany). Method and Material: In our study 33 incidental solitary pulmonary nodules (iSPNs) (28 malignant, 5 benign; mean diameter 25 +/-12mm, shortest distance to pleura 25+/-18mm) were eligible according to in- and exclusion criteria. Realtime and onsite navigation were performed according to our standard protocol.22 All iSPN were controlled with a second technique when necessary and clinical feasible in case of unspecific or unexpected histological result. In all cases common guidelines of treatment of different iSPNs were followed in a routine manner. Results: Overall navigational yield (ny) was 91% and diagnostic yield (dy) 70%, dy for all accomplished malignant cases (n=28) was 82%. In the subgroup analysis of the invisible iSPN (n=12, 11 malignant, 1 benign; mean diameter 15+/-3mm) we found an overall dy of 75%. For the first time we describe a significant difference in specifity of biopsy results in regards to the position of the forceps in the 3-dimensional volume (3DV) of the iSPN in the whole sample group. Comparing the specifity of biopsies of a 3D-uncentered but inside the outer one third of an iSPN-3DV with the specifity of biopsies of centered forceps position (meaning the inner two third of an iSPN-3DV) reveals a significant (p=0,0375 McNemar) difference for the size group (>1cm) of 0,9 for centered biopsies vs. 0,3 for uncentered biopsies. Therefore only 3D-centered biopsies should be relied on especially in case of a benign result. Conclusion:The diagnostic yield of DynaCT navigation guided transbronchial biopsies (TBB) only with forceps is at least up to twofold higher than conventional TBB for iSPNs <2cm. The diagnostic yield of DynaCT navigation guided forceps TBB in invisible SPNs is at least in the range of other navigation studies which were performed partly with multiple navigation tools and multiple instruments. For future diagnostic and therapeutic approaches it is so far the only onsite and realtime extrathoracic navigation approach (except for computed tomography (CT)-fluoroscopy) in the bronchoscopy suite which keeps the working channel open. The system purchase represents an important investment for hospitals but it is a multidisciplinary and multinavigational tool with possible access via bronchial airways, transthoracical or vascular approach at the same time and on the same table without the need for an expensive disposable instrument use.

Een zeldzame complicatie bij verwijdering van een geïmpacteerde derde molaar in de bovenkaak

A 12-year-old boy was referred by his orthodontist due to the dysmorphic condition of the impacted teeth 18 and 28. Because teeth 17 and 27 were close related to the third molars, the decision was made to remove the impacted teeth under general anaesthesia. During luxation of tooth 28, it was accidentally displaced deeper into the socket. The tooth could still not be localized after the use of radiographs, an antrostomy, and surgical exploration. It was decided to leave the 28 in its place and to perform cone beam computertomography. This showed that tooth 28 was displaced into the infratemporal fossa. Since the patient was free of symptoms, a period of watchful waiting was initiated. A control visit and cone beam computertomography 9 months postoperatively revealed no signs or symptoms or changes in the position of the displaced tooth. It was therefore decided to leave the third molar in its displaced position. Displacement of a maxillary third molar into the infratemporal fossa is considered a rare complication.

Organ doses for reference pediatric and adolescent patients undergoing computed tomography estimated by Monte Carlo simulation

To establish an organ dose database for pediatric and adolescent reference individuals undergoing computed tomography (CT) examinations by using Monte Carlo simulation. The data will permit rapid estimates of organ and effective doses for patients of different age, gender, examination type, and CT scanner model. The Monte Carlo simulation model of a Siemens Sensation 16 CT scanner previously published was employed as a base CT scanner model. A set of absorbed doses for 33 organs∕tissues normalized to the product of 100 mAs and CTDI(vol) (mGy∕100 mAs mGy) was established by coupling the CT scanner model with age-dependent reference pediatric hybrid phantoms. A series of single axial scans from the top of head to the feet of the phantoms was performed at a slice thickness of 10 mm, and at tube potentials of 80, 100, and 120 kVp. Using the established CTDI(vol)- and 100 mAs-normalized dose matrix, organ doses for different pediatric phantoms undergoing head, chest, abdomen-pelvis, and chest-abdomen-pelvis (CAP) scans with the Siemens Sensation 16 scanner were estimated and analyzed. The results were then compared with the values obtained from three independent published methods: CT-Expo software, organ dose for abdominal CT scan derived empirically from patient abdominal circumference, and effective dose per dose-length product (DLP). Organ and effective doses were calculated and normalized to 100 mAs and CTDI(vol) for different CT examinations. At the same technical setting, dose to the organs, which were entirely included in the CT beam coverage, were higher by from 40 to 80% for newborn phantoms compared to those of 15-year phantoms. An increase of tube potential from 80 to 120 kVp resulted in 2.5-2.9-fold greater brain dose for head scans. The results from this study were compared with three different published studies and∕or techniques. First, organ doses were compared to those given by CT-Expo which revealed dose differences up to several-fold when organs were partially included in the scan coverage. Second, selected organ doses from our calculations agreed to within 20% of values derived from empirical formulae based upon measured patient abdominal circumference. Third, the existing DLP-to-effective dose conversion coefficients tended to be smaller than values given in the present study for all examinations except head scans. A comprehensive organ∕effective dose database was established to readily calculate doses for given patients undergoing different CT examinations. The comparisons of our results with the existing studies highlight that use of hybrid phantoms with realistic anatomy is important to improve the accuracy of CT organ dosimetry. The comprehensive pediatric dose data developed here are the first organ-specific pediatric CT scan database based on the realistic pediatric hybrid phantoms which are compliant with the reference data from the International Commission on Radiological Protection (ICRP). The organ dose database is being coupled with an adult organ dose database recently published as part of the development of a user-friendly computer program enabling rapid estimates of organ and effective dose doses for patients of any age, gender, examination types, and CT scanner model.

Evaluation of heterogeneity dose distributions for Stereotactic Radiotherapy (SRT): comparison of commercially available Monte Carlo dose calculation with other algorithms

BackgroundThe purpose of this study was to compare dose distributions from three different algorithms with the x-ray Voxel Monte Carlo (XVMC) calculations, in actual computed tomography (CT) scans for use in stereotactic radiotherapy (SRT) of small lung cancers.MethodsSlow CT scan of 20 patients was performed and the internal target volume (ITV) was delineated on Pinnacle3. All plans were first calculated with a scatter homogeneous mode (SHM) which is compatible with Clarkson algorithm using Pinnacle3 treatment planning system (TPS). The planned dose was 48 Gy in 4 fractions. In a second step, the CT images, structures and beam data were exported to other treatment planning systems (TPSs). Collapsed cone convolution (CCC) from Pinnacle3, superposition (SP) from XiO, and XVMC from Monaco were used for recalculating. The dose distributions and the Dose Volume Histograms (DVHs) were compared with each other.ResultsThe phantom test revealed that all algorithms could reproduce the measured data within 1% except for the SHM with inhomogeneous phantom. For the patient study, the SHM greatly overestimated the isocenter (IC) doses and the minimal dose received by 95% of the PTV (PTV95) compared to XVMC. The differences in mean doses were 2.96 Gy (6.17%) for IC and 5.02 Gy (11.18%) for PTV95. The DVH's and dose distributions with CCC and SP were in agreement with those obtained by XVMC. The average differences in IC doses between CCC and XVMC, and SP and XVMC were -1.14% (p = 0.17), and -2.67% (p = 0.0036), respectively.ConclusionsOur work clearly confirms that the actual practice of relying solely on a Clarkson algorithm may be inappropriate for SRT planning. Meanwhile, CCC and SP were close to XVMC simulations and actual dose distributions obtained in lung SRT.

CHARACTERIZATION OF A COMMERCIALLY-AVAILABLE, OPTICALLY-STIMULATED LUMINESCENT DOSIMETRY SYSTEM FOR USE IN COMPUTED TOMOGRAPHY

Optically-stimulated luminescent (OSL) nanoDot dosimeters, commercially available from Landauer, Inc. (Glenwood, IL), were assessed for use in computed tomography (CT) for erasure and reusability, linearity and reproducibility of response, and angular and energy response in different scattering conditions. Following overnight exposure to fluorescent room light, the residual signal on the dosimeters was 2%. The response of the dosimeters to identical exposures was consistent, and reported doses were within 4% of each other. The dosimeters responded linearly with dose up to 1 Gy. The dosimeter response to the CT beams decreased with increased tube voltage, showing up to a -16% difference when compared to a 0.6-cm(3) NIST-traceable calibrated ionization chamber for a 135 kVp CT beam. The largest range in percent difference in dosimeter response to scatter at central and peripheral positions inside CTDI phantoms was 14% at 80 kVp CT tube voltage, when compared to the ionization chamber. The dosimeters responded uniformly to x-ray tube angle over the ranges of increments of 0° to 75° and 105° to 180° when exposed in air, and from 0° to 360° when exposed inside a CTDI phantom. While energy and scatter correction factors should be applied to dosimeter readings for the purpose of determining absolute doses, these corrections are straightforward but depend on the accuracy of the ionization chamber used for cross-calibration. The linearity and angular responses, combined with the ability to reuse the dosimeters, make this OSL system an excellent choice for clinical CT dose measurements.

Implementation of radiochromic film dosimetry protocol for volumetric dose assessments to various organs during diagnostic CT procedures.

The authors present a means to measure high-resolution, two-dimensional organ dose distributions in an anthropomorphic phantom of heterogeneous tissue composition using XRQA radiochromic film. Dose distributions are presented for the lungs, liver, and kidneys to demonstrate the organ volume dosimetry technique. XRQA film response accuracy was validated using thermoluminescent dosimeters (TLDs). XRQA film and TLDs were first exposed at the center of two CTDI head phantoms placed end-to-end, allowing for a simple cylindrical phantom of uniform scatter material for verification of film response accuracy and sensitivity in a computed tomography (CT) exposure geometry; the TLD and film dosimeters were exposed separately. In a similar manner, TLDs and films were placed between cross-sectional slabs of a 5 yr old anthropomorphic phantom's thorax and abdomen regions. The anthropomorphic phantom was used to emulate real pediatric patient geometry and scatter conditions. The phantom consisted of five different tissue types manufactured to attenuate the x-ray beam within 1%-3% of normal tissues at CT beam energies. Software was written to individually calibrate TLD and film dosimeter responses for different tissue attenuation factors, to spatially register dosimeters, and to extract dose responses from film for TLD comparison. TLDs were compared to film regions of interest extracted at spatial locations corresponding to the TLD locations. For the CTDI phantom exposure, the film and TLDs measured an average difference in dose response of 45% (SD +/- 2%). Similar comparisons within the anthropomorphic phantom also indicated a consistent difference, tracking along the low and high dose regions, for the lung (28%) (SD +/- 8%) and liver and kidneys (15%) (SD +/- 4%). The difference between the measured film and TLD dose values was due to the lower response sensitivity of the film that arose when the film was oriented with its large surface area parallel to the main axis of the CT beam. The consistency in dose response difference allowed for a tissue specific correction to be applied. Once corrected, the average film response agreed to better than 3% (SD +/- 2%) for the CTDI scans, and for the anthropomorphic phantom scans: 3% (SD +/- 3%) for the lungs, 5% (SD +/- 3%) for the liver, and 4% (SD +/- 3%) for the kidneys. Additionally, XRQA film measured a heterogeneous dose distribution within the organ volumes. The extent of the dose distribution heterogeneity was not measurable with the TLDs due to the limitation on the number of TLDs loadable in the regions of the phantom organs. In this regard, XRQA film demonstrated an advantage over the TLD method by discovering a 15% greater maximum dose to lung in a region unmeasured by TLDs. The films demonstrated a lower sensitivity to absorbed dose measurements due to the geometric inefficiency of measuring dose from a beam situated end-on to the film. Once corrected, the film demonstrated equivalent dose measurement accuracy as TLD detectors with the added advantage of relatively simple measurement of high-resolution dose distributions throughout organ volumes.

SU-GG-I-55: Dosimetric Quantities for Computed Tomography Examinations of Paediatric Patients on the Thoracic and Abdominal Regions

Purpose: To determine the value of the dosimetric quantities for the Computed Tomography(CT) paediatric examinations of the thoracic and abdominal regions. The protocols studied were those of chest, abdomen, abdomen/pelvis, chest/abdomen/pelvis, pulmonary and mediastine/abdomen, which are the more common examinations performed at the “Hospital Infantil de Mexico Federico Gomez” in these regions. Method and Materials: The measurements were performed on a Siemens SOMATOM Sensation 16 CT Scanner and the equipment used were a CT pencil ionization chamber connected to an electrometer, both calibrated for CT beam qualities and a PMMA phantom with diameter of 16 cm and length of 15 cm. Results: The dosimetric quantities measured were the weighted air kerma index (Cw), the volumetric kerma index (Cvol) and the CT air kerma—length product. It was found that the pulmonary examination presented the highest values for the dosimetric quantities; 31.1 mGy for Cw and 11.1 mGy for Cvol. The examination with the lowest values was the chest/abdomen protocol with 10.47 mGy for Cw and 5.5 mGy for Cvol. Conclusion: There are few publications about the dosimetric quantities for CT on pediatric patients and the reported does not consider the different kinds of examinations of the chest, pelvis and abdomen. This work shows that there is a strong dependence between the protocol used and the imparted dose due to the different values of current and slice thickness. Then, it is important to have a carefully selection of the protocol for the examinations. The values obtained on this work may also serve as diagnostic reference levels for further studies.

Photoelectric‐enhanced radiation therapy with quasi‐monochromatic computed tomography

Photoelectric-enhanced radiation therapy is a bimodal therapy, consisting of the administration of highly radiation-absorbing substances into the tumor area and localized regional irradiation with orthovoltage x-rays. Irradiation can be performed by a modified computed tomography (CT) unit equipped with an additional x-ray optical module which converts the polychromatic, fan-shaped CT beam into a monochromatized and focused beam for energy-tuned photoelectric-enhanced radiotherapy. A dedicated x-ray optical module designed for spatial collimation, focusing, and monochromatization was mounted at the exit of the x-ray tube of a clinical CT unit. Spectrally resolved measurements of the resulting beam were performed using an energy-dispersive detection system calibrated by synchrotron radiation. The spatial photon fluence was determined by film dosimetry. Depth-dose measurements were performed and compared to the polychromatic CT and a therapeutic 6 MV beam. The spatial dose distribution in phantoms using a rotating radiation source (quasimonochromatic CT and 6 MV, respectively) was investigated by gel dosimetry. The photoelectric dose enhancement for an iodine fraction of 1% in tissue was calculated and verified experimentally. The x-ray optical module selectively filters the energy of the tungsten Kalpha emission line with an FWHM of 5 keV. The relative photon fluence distribution demonstrates the focusing characteristic of the x-ray optical module. A beam width of about 3 mm was determined at the isocenter of the CT gantry. The depth-dose measurements resulted in a half-depth value of approximately 36 mm for the CT beams (quasi-monochromatic, polychromatic) compared to 154 mm for the 6 MV beam. The rotation of the radiation source leads to a steep dose gradient at the center of rotation; the gel dosimetry yields an entrance-to-peak dose ratio of 1:10.8 for the quasi-monochromatic CT and 1:37.3 for a 6 MV beam of the same size. The photoelectric dose enhancement factor increases from 2.2 to 2.4 by using quasi-monochromatic instead of polychromatic radiation. An additional increase in the radiation dose by a factor of 1.4 due to the focusing characteristic of the x-ray optical module was calculated. Photoelectric-enhanced radiation therapy based on a clinical CT unit combined with an x-ray optical module is a novel therapy option in radiation oncology. The optimized quasi-monochromatic radiation is strongly focused and ensures high photoelectric dose enhancement for iodine.

Assessment of the blood supply to the lingual surface of the mandible for reduction of bleeding during implant surgery

The aim of this study was to assess the frequency of the foramina and their canals on the lingual surface of the mandible using computed tomography (CT), which was carried out for dental implant planning. First, the visibility of the lingual canals of the CT image was verified by dissecting five cadavers. CT images of 200 patients, who had decided on implant treatment, were used in this study. The visibility of the foramina and their canals on the lingual surface of the mandible were assessed. The foramina were divided into two groups by the positions of the mandible, the medial lingual foramen and the lateral lingual foramen. At least one foramen was found in all patients. In the medial group, a higher level of mental spine was seen in 190 patients, the same level of mental spine was observed in 99 patients and a lower level of mental spine was observed in 114 patients. The lateral lingual foramina were found in 160/200 patients and 88/200 patients presented bilaterally. CT can predict the position and the size of the foramina and their canals on the lingual surface of the mandible. All the patients had more than one foramen in the middle of the lingual surface of the mandible on the CT image. The frequency of the lingual foramina in the medial region was 100% and that in the lateral region was 80%. It would also be useful to emphasize the significant variation in the precise location of these lingual foramina, and that these can only be visualized presurgically with volumetric imaging modalities, such as CT or Cone beam 3D systems.

Dosimetric characterisation of bismuth shields in CT: measurements and Monte Carlo simulations

Although bismuth shields are frequently used in radiology to reduce radiation dose, its mechanism has not been fully investigated. Dosimetric characteristics of bismuth shields in computed tomography (CT) were assessed with ion chamber and Monte Carlo (MC) simulations. Primary attenuation and backscatter effects of paediatric (2-ply) and adult (4-ply) bismuth shields were measured. Simulated CT beams were used for ion chamber measurements. Radiation doses were measured free-in-air and in the tissue-equivalent slabs. MC simulations for the same settings were also performed. Mean dose reductions from primary attenuation were 23% (2-ply) and 40% (4-ply). The dose increase from backscatter was 2% for both shields. MC simulations for primary beam dose reduction were 20% (2-ply) and 38% (4-ply); the backscatter dose increase was around 6% for both shields. In summary, primary attenuation is the major factor that introduces the dose reduction in bismuth and the dose increase from backscatter is negligible.

Multiscale registration of planning CT and daily cone beam CT images for adaptive radiation therapy

Adaptive radiation therapy (ART) is the incorporation of daily images in the radiotherapy treatment process so that the treatment plan can be evaluated and modified to maximize the amount of radiation dose to the tumor while minimizing the amount of radiation delivered to healthy tissue. Registration of planning images with daily images is thus an important component of ART. In this article, the authors report their research on multiscale registration of planning computed tomography (CT) images with daily cone beam CT (CBCT) images. The multiscale algorithm is based on the hierarchical multiscale image decomposition of E. Tadmor, S. Nezzar, and L. Vese [Multiscale Model. Simul. 2(4), pp. 554-579 (2004)]. Registration is achieved by decomposing the images to be registered into a series of scales using the (BV, L2) decomposition and initially registering the coarsest scales of the image using a landmark-based registration algorithm. The resulting transformation is then used as a starting point to deformably register the next coarse scales with one another. This procedure is iterated at each stage using the transformation computed by the previous scale registration as the starting point for the current registration. The authors present the results of studies of rectum, head-neck, and prostate CT-CBCT registration, and validate their registration method quantitatively using synthetic results in which the exact transformations our known, and qualitatively using clinical deformations in which the exact results are not known.

SU‐GG‐I‐42: An Anthropomorphic Adult Physical Phantom and Fiber Optic Coupled Point Dosimetry System for the Measurement of Effective and Average Organ Doses of CT Patients

Purpose: Advances in computed tomography (CT) acquisition techniques, primarily multi‐detector CT (MDCT) and cone beam CT (CBCT), make it highly desirable to develop measurement techniques that provide a more physically meaningful measurement of patient dose than the traditional CT dose index (CTDI). The goal of this work was to accurately quantify the organ doses delivered to adult patients during CT exams as a fundamental tool for developing patient dose histories. Method and Materials: A tissue‐equivalent anthropomorphic adult phantom based on a tomographic data set was developed and fabricated at the University of Florida. The adult phantom's physical and radiological parameters are designed to mimic ICRP reference man, and include tissue‐equivalent materials for soft tissue, bone, and lung. Fiber optic‐coupled (FOC) dosimeters, which have been calibrated and characterized across the CT energy range, provide point dose measurements for multiple organ locations. The combination of phantom and FOC dosimeters establishes a dosimetry system to characterize both internal organ doses and effective dose. Results: The calibrated point detector system provides remote, real‐time dose measurements and in conjunction with the adult physical phantom allows for the quantification of absorbed organ dose measurements for a wide range of MDCT acquisition protocols. Average organ doses were quantified for the prostate, kidneys, liver, and lungs. The point dosimeter measurement illustrates the significant dose contributions that originate from scattering outside of tissue regions represented by the 15 cm length of CTDI phantoms. FOC dosimeters permit the dose to be displayed as a function of longitudinal position for a variety of scan parameters, aiding in the interpretation of dose comparisons. Conclusion: FOC dosimeters demonstrate high sensitivity, reproducibility, excellent dose linearity, and combined with their small physical size permit accurate point‐dose measurements. The organ doses vary significantly from interpretations of the CTDI, depending strongly on position and scan volume.

SU‐FF‐I‐51: Effect of Subcutaneous Fat On Abdominal CT Dosimetry: Monte Carlo Study

Purpose: To investigate the effect of abdominal subcutaneous fat on organ and effective doses in abdominal computed tomography (CT) examination by using deformable hybrid anthropomorphic phantoms and MCNPX2.5. Methods and Material: A hybrid anthropomorphic computational phantom representing a newborn reference patient was employed in this study to illustrate use of deformable phantoms for patient‐specific dosimetry. The hybrid phantom is currently the most advanced computational phantom incorporating the best features of conventional stylized and voxel phantoms, which include parameter‐based flexibility and improved anatomical realism, respectively. Based on the template phantom of which the abdominal circumference was 36 cm, two more phantoms having abdominal circumferences of 33 and 39 cm were generated by manipulating control points on the abdominal surfaces. Three phantoms were then incorporated into MCNPX2.5 code where helical fan beams from SOMATOM Sensation 16 helical multi‐slice CT scanner were modeled. A CT collimator setting of 12 mm and a tube potential of 100 kVp, both commonly used in pediatric CT scans, were simulated for illustrative calculations. Absorbed doses for major organ doses were calculated in each of the three newborn phantoms. The normalized organ absorbed doses for a total of 9 major organs were calculated and compared to each other. Results: As waist circumference increases, the thickness of abdominal subcutaneous fat increases correspondingly which causes a decrease in the organ absorbed dose for CT beams, especially, for the small intestinal wall (−5.8%) and kidney (−7.3%). Conclusion: Even though the effect of fat thickness on organ dose was not significant in newborn phantom, higher correlation would be observed in older and larger phantoms. The authors are working on a series of pediatric phantoms so that a more systematic investigation on the effect of abdominal subcutaneous fat on CT dosimetry could be performed in the future.

Cardiac Computed Tomography: Is It Ready For Primetime?

INTRODUCTION The last decade has witnessed dramatic improvements in computed tomography (CT) technology with the development of both electron beam (EB) and multi-detector (MD ) CT systems. EBCT provided the first attempt at high-resolution “freeze frame” images of the heart and coronary arteries, with 50 msec image acquisition times obviating distortion and blurring of the continuously moving myocardium. Developments in MDC T have included increasing gantry speeds to improve temporal resolution and the addition of multiple detector arrays that allow submillimeter spatial resolution and reduced image acquisition times. Although EBCT has higher temporal resolution than MDCT and lower radiation exposure through prospective triggering of the X-ray beam at a specific time in the cardiac cycle, MDCT provides higher spatial resolution and is generally more accessible to the medical community. Both techniques can be used to assess cardiac structure, determine the presence and extent of coronary artery calcificati...

Measurement of CT radiation profile width using CR imaging plates

This paper describes the procedure for using a Fuji computed radiography (CR) imaging plate (IP) for the measurement of computed tomography (CT) radiation profiles. Two sources of saturation in the data from the IP, signal and quantization, were characterized to establish appropriate exposure and processing conditions for accurate measurements. The IP generated similar profiles compared to those obtained from digitized ready-pack films, except at the profile edges, where the exposure level is low. However, when IP pixel values are converted to exposure, CR and digitized film profiles are in agreement. The full width at half maximum (FWHM) of the CT radiation profile was determined from the relationship between pixel value and exposure and compared to FWHM of the digitized optical density profile from film. To estimate the effect of scattering by the cassette material, radiation profiles were acquired from IPs enclosed in a cassette or in a paper envelope. The presence of the cassette made no difference in the value determined for FWHM. With proper exposure and processing conditions, the FWHM of 5, 10, and 15 mm collimated beams were measured using IPs to be 7.1, 11.9, and 17.0 mm and using film to be 7.2, 12.2, and 16.8 mm, respectively. Our results suggest that, under appropriate conditions, the estimation of the width of the CT radiation profile using Fuji CR is comparable to the measurement from film density described in American Association of Physicists in Medicine (AAPM) Report No. 39. Although our experiment was conducted using Fuji CR, we anticipate that CR plates from other vendors could be successfully used to measure CT beam profiles because of similar empirical relationships between pixel value and exposure.

ACR Clinical Statement on Noninvasive Cardiac Imaging

Coronary artery disease and other acquired and congenital cardiac diseases are major medical and socio-economic problems. Historically, imaging has had a critical role in the diagnosis and evaluation of acquired and congenital cardiac disease. Advances in computed tomography (CT), with multidetector CT and electron beam CT technology, and magnetic resonance (MR) imaging, now make it possible to noninvasively image the coronary arteries, cardiac chambers, valves, myocardium, and pericardium and assess cardiac function, and CT and MR imaging are becoming increasingly important in the evaluation of cardiac disease. Radiologists, because of their extensive experience in CT and MR imaging, have an important role in imaging cardiac patients using these modalities. This clinical statement of the ACR discusses various technical and patient safety issues related to cardiac CT and MR imaging, and it suggests appropriate qualifications for radiologists until such time as ACR practice guidelines for the performance of cardiac CT and cardiac MR imaging are written and approved through the usual ACR process. It stresses that the interpreting physician is responsible for examining not only the cardiac structures of interest but also all the visualized noncardiac structures and must report any clinically relevant abnormalities of these adjacent structures.

Coronary Calcification, Coronary Disease Risk Factors, C-Reactive Protein, and Atherosclerotic Cardiovascular Disease Events: The St. Francis Heart Study

The purpose of this study was to determine the prognostic accuracy of electron beam computed tomographic (CT) scanning of the coronary arteries and the relationship of coronary calcification to standard coronary disease risk factors and C-reactive protein (CRP) in the prediction of atherosclerotic cardiovascular disease (ASCVD) events in apparently healthy middle-age persons. As a screening test for coronary artery disease (CAD), electron beam CT scanning remains controversial. In a prospective, population-based study, 4,903 asymptomatic persons age 50 to 70 years underwent electron beam CT scanning of the coronary arteries. At 4.3 years, follow-up was available in 4,613 participants (94%), and 119 had sustained at least one ASCVD event. Subjects with ASCVD events had higher baseline coronary calcium scores (median [interquartile range], Agatston method) than those without events: 384 (127, 800) versus 10 (0, 86) (p < 0.0001). For coronary calcium score threshold > or = 100 versus < 100, relative risk (95% confidence interval) was 9.6 (6.7 to 13.9) for all ASCVD events, 11.1 (7.3 to 16.7) for all CAD events, and 9.2 (4.9 to 17.3) for non-fatal myocardial infarction and death. The coronary calcium score predicted CAD events independently of standard risk factors and CRP (p = 0.004), was superior to the Framingham risk index in the prediction of events (area under the receiver-operating characteristic curve of 0.79 +/- 0.03 vs. 0.69 +/- 0.03, p = 0.0006), and enhanced stratification of those falling into the Framingham categories of low, intermediate, and high risk (p < 0.0001). The electron beam CT coronary calcium score predicts CAD events independent of standard risk factors, more accurately than standard risk factors and CRP, and refines Framingham risk stratification.

Radiation dose in computed tomography of the heart.

Currently, computed tomographic (CT) imaging of the heart is mainly used for the quantification of coronary artery calcification as an indirect measure of coronary plaque burden1,2 and, less frequently, for minimally invasive coronary angiography.3 CT imaging of the heart and coronary arteries without unsharpness due to motion artifact first became possible with the introduction of electron beam computed tomography (EBCT) in 1983.4 More recently, so-called multislice spiral computed tomographic (MSCT) scanners with gantry rotation speeds fast enough to produce diagnostic images of the heart under certain conditions have become widely available.5 As a consequence, cardiac CT imaging, most often performed for the purpose of calcium scoring,2 is increasingly applied to the general public. In many centers, patients have access to such studies without physician referral. This has created concerns for public health because of the radiation dose associated with CT imaging.6–8 Many clinicians and researchers working with patients with cardiovascular diseases may yet be unfamiliar with the radiation doses that are received during various cardiac CT imaging protocols and how they differ between the various scanner types that are currently used. To further complicate matters, radiation dose estimates can be expressed in various ways. For these reasons, the doses reported in previous publications on cardiac CT have varied widely, and it is not always clear what parameters were being reported.3,9–11 The purpose of this article is to discuss the current concepts of radiation dose measurement and estimation in CT imaging and to provide comparative estimates for radiation doses received during cardiac examinations with use of EBCT or MSCT. This information may be helpful to physicians who perform calcium scoring, counsel patients contemplating cardiac calcium scoring, or are considering referring their patients for such studies. EBCT scanners acquire 1 scan at a time, using …