Radiation dose and image quality in spiral computed tomography: multicentre evaluation at six institutions

The purpose of this study was to evaluate the correlation of radiation dose with image quality in spiral CT. Seven clinical protocols were measured in six different radiological departments provided with four different types of high specification spiral CT scanners. Central and surface absorbed doses were measured in acrylic. The practical CT dose index (PCTDI) was calculated for seven clinical examination protocols and one standardized protocol using identical parameters on four different spiral CT scanners with a dedicated ionization chamber inserted into PMMA phantoms. For low contrast measurements, a cylindrical three-dimensional (3D) phantom (different sized spheres of defined contrast) was used. Image noise was measured with a cylindrical water phantom and high contrast resolution with a Perspex hole phantom. Image quality phantoms were scanned using the parameters of the clinical protocols. Images were randomized, blinded and read by six radiologists (one from each institution). PCTDI values for four different scanners varied up to a factor between 1.5 (centre) and 2.2 (surface) for the standardized protocol. A greater degree of variation was observed for seven clinical examination protocols of the six radiological departments. For example, PCTDI varied up to a factor between 1.7 (cerebrum protocol) and 8.3 (abdomen paediatric protocol). Low contrast resolution correlates closely with dose. An improvement in detection from 8 mm to 4 mm sized spheres needs approximately a ten-fold increase in dose. Noise shows a moderate correlation with PCTDI. High contrast resolution of clinical protocols is independent of PCTDI within a certain range. Differences in modern CT scanner technology seem to be of less importance for radiation exposure than selection of protocol parameters in different radiological institutes. Future discussion on guidelines regarding optimal (patient adapted) tube current for clinical protocols is desirable.     

An anthropomorphic phantom study on the effect of midvertebral slice placement and region-of-interest positioning on the reproducibility of single-energy quantitative CT (QCT) of the spine

PURPOSE: The purpose of our study was to develop an anthropomorphic phantom with a 3D external reference system capable of geometrically describing the region of interest (ROI) of single-energy quantitative CT (QCT) scans and to study the reproducibility of ROI placement (volume) and bone mineral density (BMD) after operator-defined and algorithm-supported midvertebral slice (MVS) placement. METHOD: In three vertebrae (L1-3) of 10 human cadaveric spines placed in a water phantom, MVSs were defined by an operator and an algorithm-supported technique on lateral digital CT radiographs, and QCT scans were performed accordingly. The measurements were repeated once after repositioning the phantom on the CT table. ROIs of the trabecular bone were determined with a standard technique. The percentage of bone volume was calculated for one ROI not covered by the repetition (volume mismatch percent). RESULTS: Reproducibility with algorithm-supported MVS placement was superior to that of operator-defined positioning with regard to volume mismatch (mean +/- SD): 10.6+/-8.4 vs. 7.9+/-5.3%; and mean of paired BMDs (mean of three vertebral bodies): 2.7 vs. 1.5% (p < 0.05). CONCLUSION: The ROI volume mismatch of repeated QCT scans, which is approximately 10% of ROI volume, can be quantified with an external reference system. Automated placement is superior to the manual technique and should be used in clinical practice.     

Atherosclerotic plaque components in human aortas contrasted by ex vivo imaging using fast spin-echo magnetic resonance imaging and spiral computed tomography

RATIONALE AND OBJECTIVES: Imaging techniques that distinguish atherosclerotic plaque components may be useful in identifying the nature of the atherosclerotic lesion and determining the best method of treatment for obstructive vascular mining the best method of treatment for obstructive vascular disease. This study compares fast spin-echo (FSE) magnetic resonance (MR) and spiral computed tomography (CT) images of excised human atherosclerotic aortas to determine which imaging technique provides the best contrast between plaque components ex vivo. METHODS: Aortas were imaged using four FSE sequences in MR with and without frequency-selective fat saturation, and using spiral CT without contrast. The average signal intensity of a region of calcification, thrombosis, fatty plaque, and normal vessel wall was measured on all images and compared. RESULTS: The use of fat saturation pulses in MR did not significantly alter the signal from atherosclerotic plaque for the sequences used. Proton density-weighted FSE sequences that collected early echoes were better than other FSE sequences and CT at differentiating calcification from all soft tissues. T2-weighted FSE sequences that collected later echoes were best at soft-tissue discrimination. CONCLUSIONS: The FSE techniques used were superior to nonenhanced spiral CT in discriminating plaque components ex vivo, including calcification.     

Multiplanar imaging in the preoperative assessment of metallic intraocular foreign bodies. Helical computed tomography versus conventional computed tomography

OBJECTIVE: This study aimed to compare the effectiveness of helical computed tomography (CT) versus conventional CT in the preoperative assessment of metallic intraocular foreign bodies on axial, coronal, and multiplanar reconstruction images in clinical routine. DESIGN: Prospective comparative trial, alternate assignment of consecutive patients. PARTICIPANTS: Eighteen patients with penetrating eye injuries and suspected metallic intraocular foreign bodies were studied. INTERVENTION: Alternate patients were assigned to undergo either helical CT or conventional CT in the axial plane. Both the helical and the conventional data were transferred to a workstation, and reconstructions in the coronal and sagittal planes were performed. Additional direct coronal scanning was performed only when necessary for preoperative assessment. MAIN OUTCOME MEASURES: The quality of the directly obtained axial and coronal, as well as the reconstructed coronal and sagittal images, was assessed for each, imaging method based on the ability to detect and accurately localize foreign bodies. The size of the foreign bodies was measured and compared to the actual diameter. Total examination time and radiation dose delivered to the lens were measured for each imaging method. RESULTS: All foreign bodies were detected by each scanning method on the axial, the coronal, and on the reconstructed planes. The quality of the axial images was similar for helical and conventional CT. The helical technique provided high-quality reconstructed images comparable in quality to the directly obtained coronal planes in conventional CT. Reconstructions by conventional technique were not useful for preoperative assessment. The examination time for the total orbital volume was 18 seconds for helical CT examinations and 52 seconds for conventional CT examinations. Radiation dose delivered to the lens for the complete examination was 35 mGy for helical CT axial scanning, 56 mGy for conventional CT axial scanning, and 63 mGy for conventional CT coronal scanning. CONCLUSIONS: Helical CT multiplanar imaging offers several significant advantages for the preoperative assessment of metallic intraocular foreign bodies compared to the conventional CT technique in clinical practice, including short examination time, reduced motion artifacts, reduced radiation exposure, and the ability to obtain diagnostically useful coronal and sagittal reconstruction images without the need for additional scanning.     

Electron-beam computed tomography: preliminary experiences in the Netherlands]

The difference between computer tomography (CT) and electron beam tomography (EBT) is that for CT the x-ray tube rotates in a ring round the patient, and for EBT the x-ray beam rotates itself. As a result, with EBT the speed of making images is not limited by the mechanical rotation of the tube, and 16 images can be made per second. An EBT scan of a whole thorax takes 9 seconds. Specific application areas are fast moving organs and patients who cannot remain in one position for long, e.g. children and intensive care patients. Research is being conducted into the possibilities of this non-invasive technique for the demonstration of coronary artery lesions, pulmonary embolism, pulmonary metastases and dynamic examination of the major respiratory tract. Costs of an EBT scan currently amount to Dfl. 450.--but they will probably decrease as this imaging system is developed further. The exposure to radiation is about the same as that caused by a (spiral) CT.     

Vesicouterine fistula twenty years following brachytherapy for cervical cancer

Assessment of maternal pelvic dimensions is usually considered necessary where vaginal delivery is contemplated in a breech presentation or if reduced pelvic dimensions are suspected in a current or previous pregnancy. Pelvimetry techniques include computed tomography (CT), conventional radiography, digital fluorography and magnetic resonance imaging (MRI). The first three techniques result in a radiation dose to mother and fetus which, depending on how the technique is performed, can vary by up to 40-fold. Of the techniques using X-rays, CT pelvimetry with a lateral scanogram generally gives the lowest radiation dose and conventional radiography using an air gap technique with a single lateral view is a relatively low-dose alternative where CT is not available. A questionnaire was sent to 227 hospitals during 1993 and 1996 to assess whether there was a move towards lower dose techniques of pelvimetry. The results show a trend away from conventional pelvimetry (48.4% in 1993 to 28% in 1996) with a small proportion of centres using MRI (4%) in 1996. Of the centres still using conventional pelvimetry, relatively few were using a low-dose air-gap technique (2.1% in 1993 to 10.9% in 1996). An increasing majority of centres were using one-view CT (69.3% in 1993 and 80.4% in 1996) but a significant proportion were still performing more than one view. This study shows that there was a move towards lower dose techniques of pelvimetry but that there were still many hospitals that had not implemented a policy of reducing radiation exposure in these patients.     

Measurement of scatter fractions in erect posteroanterior and lateral chest radiography

Scatter fractions (SFs) measured in patients undergoing erect posteroanterior (PA) and lateral chest radiography with a 12:1 antiscatter grid are reported. Modifications to the posterior beam-stop (PBS) technique allowed measurement of scatter in these patients, without altering the diagnostic image and without additional radiation exposure. The SF measurements are reported by anatomic location on 42 clinical chest images. Average SF values ranged from 0.27 to 0.90 on lateral radiographs and from 0.27 to 0.68 on PA radiographs. Scatter measurements with the 12:1 grid were found to be greater than estimates from previous PA chest phantom experiments. To the authors' knowledge, they were the first to measure radiation scatter with the PBS technique in patients undergoing PA and lateral chest radiography with the antiscatter grid.     

Technical bases and acquisition conditions of electron-beam computed tomography

PURPOSE: In this review the technical principle and scanner characteristics of electron beam computer tomography (EBCT) are discussed. METHODS: In contrast to conventional CT, image acquisition in EBCT is achieved without mechanically moving parts. This construction allows for short acquisition times in investigating given anatomical regions (100 ms per slice) or up to 8 levels without table movement and short interscan delays (50 ms per slice). RESULTS: Depending on the nature of the investigation, the scanner can be used in the single slice, continuous volume scanning and multi slice mode. The single slice mode is used for detection and quantification of coronary calcifications and for CT angiography of the coronary vessels. Equivalent to the spiral mode in conventional CT, continuous volume scanning may be used for routine investigation of the chest and abdomen. Functional investigations of the heart and perfusion measurement of different organs can be performed in multi slice mode. Because of the geometry of the electron beam scanner, radiation exposure for certain investigations is above the exposure with conventional CT. CONCLUSION: Future developments will focus on dose efficient radiation collimation, high resolution detector systems and artefact reducing reconstruction kernels.     

Accurate determination of chemical composition of urinary calculi by spiral computerized tomography

PURPOSE: Choice of efficacious clinical management of symptomatic renal calculi can be facilitated by ascertaining the precise chemical composition of the calculus. Spiral computerized tomography (CT) is becoming a frequently used radiographic examination to establish the diagnosis and severity of calculus disease. Our objective for this study was to determine the precision of spiral CT in identifying the chemical composition of 6 different types of urinary calculi with region of interest measurements using spiral CT. MATERIALS AND METHODS: A total of 102 chemically pure stones were separated into 6 groups. The stones along with phantoms containing butter (fat) and jello (water) were mounted vertically in the scanner gantry. Then 1 mm. thickness scanning was performed with a high speed scanner at the 2 energy levels of 80 and 120 kV. The determination of the chemical composition was performed using the absolute CT value measured at 120 kV. and the dual kilovolt CT values measured at 80 and 120 kV. Hounsfield unit at 80 kV.-Hounsfield unit at 120 kV.). RESULTS: The absolute CT value measured at 120 kV. was able to identify precisely the chemical composition of uric acid, struvite and calcium oxalate stones. It was imprecise in differentiating calcium oxalate from brushite stone and struvite from cystine stone. However, dual kilovolt CT value was able to differentiate these latter stones with statistical significance (p < 0.03). Uric acid stones were easily differentiated from all other stones using the absolute CT value. CONCLUSIONS: This study demonstrates that the chemical composition of urinary calculi can be accurately determined by CT scanning in an in vitro setting.     

Significance of computed tomography-measured volume in the prognosis of cervical carcinoma

BACKGROUND: Computed tomography (CT) can visualize the volume and shapes of the deep-seated tumors and is expected to predict the treatment outcome in a more quantitative manner. This study was undertaken to learn the prognostic significance of CT-provided information in the radiation therapy of carcinoma of the cervix. METHODS: One hundred thirty-one CT evaluations were systematically applied to 87 patients having carcinoma of the cervix uteri. The cervical mass volume was measured by CT at a certain phase or phases of treatment and was analyzed in relation to their local control at 3 years and the survival at 5 years. RESULTS: The initial volume, measured at the beginning of radiation therapy, was not a significant prognostic guide for the local control. However, the second volume, the volume of cervical lesion measured immediately after the completion of external irradiation, proved to be a prominent prognostic factor for both the 3-year local control and 5-year survival, regardless of the clinical stage. In 52 patients whose second volume was less than 38 cm3, 47 patients (90.4%) were locally controlled for 3 years or more after radiation therapy, whereas 17 of 23 patients (73.9%) whose second volume exceeded 38 cm3 failed in the local control. Five-year actuarial survival rate was 53.1% plus or minus 6.2% in the former group and 26.1% plus or minus 9.6% in the latter group. CONCLUSIONS: CT-aided volumetry provides for an early prediction of treatment failure in radiation therapy for cervical carcinoma.     

Depot medroxyprogesterone acetate or oral contraception in postpartum adolescents

The purpose of the study was the evaluation of low-dose spiral CT in the detection and assessment of contours of pulmonary nodules. In a prospective investigation 71 consecutive chest CT examinations were acquired both at 30 and 200 mA. Films were interpreted independently by two radiologists. According to the size, nodules were divided into four categories: 10 mm; nodule shape was registered. With both protocols, 240 nodules were detected. The correlation coefficient for both methods was 0.89. Discrepancies were found most frequently in nodules near to pulmonary vessels. Nodule size estimation did not differ more than one size category. Eight spiculated nodules were identified by both techniques. Low-dose spiral CT of the chest has a high sensitivity in the detection of pulmonary nodules. If clinical circumstances require dose minimization, low-dose spiral CT may be advocated as an alternative screening method to conventional dose spiral CT.     

Autologous latissimus breast reconstruction: a 3-year clinical experience with 100 patients

This article presents our technique of autologous breast reconstruction using the latissimus dorsi flap and studies the advantages, disadvantages, and results that can be expected. A consecutive sample of 100 patients was studied. The average length of follow-up was 20 months (range 8 to 44 months), and all of the subjects were reviewed in consultation without loss to follow-up. The supplementary volume of the latissimus dorsi was obtained from five fatty zones: fat on the cutaneous paddle, fat taken from the surface of the muscle, the scapular fat pad, the anterior fatty zone, and the supra-iliac fat pad. This technique must be measured against the transverse rectus abdominis muscle (TRAM) flap, free or pedicled, when the patient needs an autologous breast reconstruction. It can be used when the TRAM flap is contraindicated (this corresponds to 45 percent of patients of our sample) or when the dorsal donor site is preferred (55 percent of cases of our sample). The major complications are rare (1 percent partial necrosis and 1 percent total necrosis of the flap). The minor complications are represented mainly by the dorsal seroma. This is the main drawback of the technique, as it occurs in 79 percent of cases and regularly in obese patients. In view of this frequency, patients should be warned of its likely occurrence. The dorsal donor-site morbidity is relatively low; 4 percent of dorsal sequelae were classed as moderate, and 96 percent were considered low. The scapular sequelae have been classed as low in 97 percent of cases, and temporary scapular sequelae aggravation has been noted in 3 percent. Results of breast reconstruction using this technique are most encouraging. The level of patient satisfaction is high; 87 percent of them were deeply satisfied, 10 percent were satisfied, and only 3 percent were poorly satisfied. This group of poorly satisfied subjects (3 percent) consists of patients who suffered a serious postoperative complication. The aesthetic results have been judged excellent by surgeons in 85 percent of the cases, good in 12 percent of the cases, and poor in 3 percent of the cases; no result has been judged bad. This technique of breast reconstruction by autologous latissimus dorsi brings a major advance in breast reconstruction. The best indications of this technique are when one can bury the cutaneous paddle: cases of skin-sparing mastectomy, cases where the latissimus dorsi flap can be combined with an abdominal advancement flap, and cases of conversion of implant reconstruction to an autologous reconstruction.     

Induction of apoptotic cell death in human leukemic cell line, HL-60, by extremely low frequency electric magnetic fields: analysis of the possible mechanisms in vitro

An anthropomorphic Rando phantom was used to compare radiation doses sustained during helical and conventional axial CT of the pelvis. The values obtained with the Rando phantom were validated against cadaveric phantoms, and show good agreement. For the authors' particular CT unit, helical scanning was found to deliver a lower radiation dose than conventional axial scanning. This was most prominent at 1.0-s tube rotation times (average dose ratio 1.24). For realistic scanning parameters and exposure factors, the ratio of radiation dose to pelvic organs can be expected to lie in the range of 40-100 mGy. The whole-body effective dose (ED) depends on selection of scanning parameters and patients anatomy. In a favourable case scenario, the ED for CT scanning of the pelvis in a male can be expected to be between 10 and 20 mSv if the scrotum is not included in the radiation field, while the ED in a female will be approximately 20 mSv. An examination of scatter radiation fall-off curves from a single slice shows that the spread of scatter radiation is only marginally affected by slice thickness. A total of 10-12 cm of human soft tissue acts as a good barrier against internal scattered radiation. The use of such scatter fall-off curves, together with manufacturers' dosimetry specifications, allows a fast estimate of absorbed dose.     

A CT assisted method for absolute quantitation of internal radioactivity

A method is described for the determination of radioactivity (microCi or MBq) at an organ site within an object or patient. Using both anatomic image data (CT or MRI scans) and planar gamma camera images, activity at depth is determined using a matrix inversion method based on least squares. The result of the inversion analysis was the unknown set of n linear (uniform) activity densities representative of each organ within the phantom or patient. The problem was overdetermined since the number of unknown activity densities (microCi/cm) was much less than the number of analysis points (N) within the nuclear image. This method, defined as the CT assisted matrix inversion (CAMI) technique, was accurate to within 15% for a three "organ" plastic phantom, wherein the organs were right circular cylinders having activities of 74 to 508 microCi (or 2.74 MBq to 18.8 MBq). This accuracy included image quantitation effects, particularly assumptions concerning attenuation correction. The average absolute percent error of the estimated activity in four distinct radioactive volumes in the phantom was 9.8%. It was found that the background activity within the phantom was estimated to be too high if sampling regions near strong sources were used in the analysis (scatter effect). This was minimized by going at least 2 cm away from such sources. By applying the method to a monoclonal antibody clinical study, activities within the patient's major organs such as liver, spleen, and kidney could be estimated, even in cases where the organ could not be visualized. Here, the CAMI algorithm gave internally consistent results for the patient's left and right lung linear activity concentrations. The CAMI technique resolves the problem of tissue superimposition using depth information from 3-D CT and is applicable in cases where a number of organs overlap in the gamma camera image. Thus, the method should be generally useful to nuclear image quantitation and the estimation of absorbed radiation doses in patients. One particular application is the estimation of radiation doses in radioimmunotherapy (RIT).     

Radiation exposure during CT examination of thorax and abdomen. Comparison of sequential, spiral and electron beam computed tomography

Comparison of radiation exposure applied by different types of CT scanners for the investigation of the chest and abdomen. Determination of radiation exposure applied by multi-phase spiral CT. Estimation of the dose in air in the system axis of the scanner, the CT dose index (CTDI) and the effective dose for electron beam tomography (EBT) and two conventional CT scanners (sequence, SEQ; spiral, SCT). For EBT, dose in system axis for investigation of the abdomen was above 50 mGy. Effective dose for investigation of the chest and abdomen was higher with EBT (11 and 26 mSv, respectively) than with conventional CT (SEQ, 4 and 20 mSv; SCT, 2 and 7 mSv). The effective dose for a biphasic investigation (liver 5 mSv, kidney 4 mSv) was below, for a triphasic investigation (liver 7 mSv) above the effective dose of the investigation of the abdomen (6 mSv). Investigation of the abdomen with the EBT should only be performed for certain indications. With spiral CT, effective dose is much lower than with EBT.     

A new volumetric CT machine for dental imaging based on the cone-beam technique: preliminary results

The objective of this paper is to present a new type of volumetric CT which uses the cone-beam technique instead of traditional fan-beam technique. The machine is dedicated to the dento-maxillo-facial imaging, particularly for planning in the field of implantology. The main characteristics of the unit are presented with reference to the technical parameters as well as the software performance. Images obtained are reported as various 2D sections of a volume reconstruction. Also, measurements of the geometric accuracy and the radiation dose absorbed by the patient are obtained using specific phantoms. Absorbed dose is compared with that given off by spiral CT. Geometric accuracy, evaluated with reference to various reconstruction modalities and different spatial orientations, is 0.8-1% for width measurements and 2.2% for height measurements. Radiation dose absorbed during the scan shows different profiles in central and peripheral axes. As regards the maximum value of the central profile, dose from the new unit is approximately one sixth that of traditional spiral CT. The new system appears to be very promising in dentomaxillo-facial imaging and, due to the good ratio between performance and low cost, together with low radiation dose, very interesting in view of large-scale use of the CT technique in such diagnostic applications.     

Radiation dose in critical organs due to non-coplanar irradiation of the hypophysis

BACKGROUND: In order to estimate the somatic and genetic risk associated with a non-coplanar linac-based radiation technique of the pituitary gland, systematic secondary-dose measurements in a phantom and sample measurements of the dose near critical organs of patients were performed. PATIENTS AND METHODS: For measurements of the dose outside the primary radiation field an acrylic-PVC phantom was used which was irradiated with a single field (4 x 4 cm2). Eight patients with pituitary tumors were treated isocentrically with a combination of sagittal and transverse rotational arcs. To measure the dose in critical organs. LiF thermoluminescence dosimeters (TLD) in chip form were placed onto 1 eyelid, the skin over the thyroid, and the patient's clothes covering the region of breasts and ovaries of female patients and the testicles of male patients. Measurements were performed for all patients during 1 sagittal irradiation and for the majority of patients during 1 transverse irradiation. RESULTS: The phantom measurements demonstrated that the secondary dose measured on the patients surface can be considered as a good approximation for the dose in adjacent organs. The median dose in critical organs for sagittal irradiation was in the range of 25.8 mGy (eyes) to 1.9 mGy (testicles), and for transverse irradiation in the range of 23.3 mGy (eyes) to 1.3 mGy (testicles). The ratio of median organ doses for sagittal and transverse irradiation was 2.1 for the thyroid gland, 1.1 for the eyes, and 1.5 for the other organs. CONCLUSIONS: The dose in critical organs due to non-coplanar irradiation of the pituitary gland is only a small fraction of the dose delivered to the reference point of the planning target volume. The risk of a radiation-induced tumor and a genetic consequence associated with these small doses is generally less than 1% and 0.1%, respectively.     

Surgical margins and prognostic factors in patients with thick (>4mm) primary melanoma

PURPOSE: The aim of this project was to analyze and validate the diagnostic applications of Volumetric High Resolution CT in the study of focal or diffuse infiltrative lung disease compared with High Resolution CT. To date HRCT is the gold standard in the assessment of infiltrative lung diseases, but it shows some limitations such as artifacts due to both respiratory and cardiac motions, as well as the need for multiple breath-holds. MATERIAL AND METHODS: September, 1996, to September, 1997, anthropomorphic test phantoms and a group of 34 subjects (8 without lung disease and 26 with aspecific lung disease: TBC, BPCO, micronodular conditions, cardiogenic interstitial pulmonary edema) were submitted to both HRCT and VHRCT. VHRCT was carried out with a 3-mm slab thickness and the images were reconstructed with a 1-mm interval and processed with MIP and MinIP reconstructions. With both techniques we compared some physical parameters (slice sensitivity profile, noise, longitudinal resolution) and some radiographic findings (central and peripheral airways lumen, peripheral vessels, nodular and interstitial abnormalities, emphysema foci, focal areas of ground glass pattern and bronchiectasis). We calculated the radiation exposure dose of both HRCT and VHRCT, also testing a low-dose protocol. RESULTS: The analysis of physical parameters showed no major differences between HRCT and VHRCT regarding longitudinal resolution, while minimal advantages were found with HRCT for slice sensitivity profile and image noise. Radiographic analysis showed additional findings in 27% of patients with nodular disease using VHRCT-MIP in 8% of patients with emphysema and 25% of cases with focal areas of ground glass opacities, using VHRCT-MinIP. Relative to HRCT findings, VHRCT better depicted all patterns but subpleural nodules. The surface radiation dose was 2.8 times higher with VHRCT than HRCT. It is possible to halve radiation exposure using a low dose protocol (120 kV, 110-150 mA). CONCLUSIONS: Our study provides conclusive results concerning the use of VHRCT with standard technical parameters because this technique showed some advantages in the study of a wide range of diffuse or focal lung diseases. We suggest that this protocol be applied only in patients with mild forms of lung disease or in the cases of difficult interpretation, such as suspicious abnormal areas at HRCT, because its doses are higher. Out low-dose protocol is currently on trial but we expect promising results.     

An automated image-registration technique based on multiple structure matching

A new image-registration technique that matches multiple structures on complementary imaging data sets (e.g., CT and MRI) has been developed and tested with both phantom and patient data. The algorithm assumes a rigid-body transformation and is suitable for correlating structures within the cranium or at the skull base. The basic premise of the new technique is that an optimum transformation is achieved when the relative volume lying outside of the intersection between a structure and its transformed counterpart is a minimum. This relative volume is calculated numerically using a random sampling approach, and a binary searching algorithm was used to step through the nine-dimensional parameter space consisting of three rotation angles, three scaling factors and three components of a translation vector. For the nine tests using phantom data, the automated structure-matching technique was able to predict the correct rotation angles to within +/- 1 degree. The expected clinical performance of the new technique was assessed by comparing results obtained with the new method to those obtained using other techniques for 12 patients who were treated with charged particles at Lawrence Berkeley Laboratory (LBL) and who had image-registration studies performed as part of their treatment plan. For 9 of the 12 patients considered, the new structure-matching technique produced a significantly better registration than the older methods, as measured by the resultant average relative volume lying outside of the intersection between any structure and its transformed counterpart. For the other three patients, results were not significantly different for the new structure-matching method and the older techniques.     

Detection of coronary artery calcifications predicting coronary heart disease: comparison of fluoroscopy and spiral CT

The aim of this study was to evaluate the clinical relevance of coronary artery calcifications detected by spiral CT, congruence with fluoroscopy (FS) and coronary angiography, and comparison with studies reporting on application of double-helical CT and ultrafast CT. Forty patients underwent spiral CT (2-mm slice thickness, table feed 3 mm/s), coronary angiography, and FS (performed in the usual manner). Stenosis and calcifications were evaluated semiquantitatively. Nineteen patients suffering from a stenosis >/= 75 % were verified at coronary angiography. All had coronary artery calcification on spiral CT. Fluoroscopy did not detect 8 of 19 patients with a stenosis >/= 75 % (1 vessel: n = 1; 2 vessels: n = 3; 3 vessels: n = 4). In spiral CT sensitivity was 100 % and specificity was 33 % (FS: 58 and 48 %). Positive predictive value was 83 % for spiral CT (FS: 50 %), and negative predictive value was 100 % (FS: 56 %). A significant linear increase in the calcification score was found for increasing maximal stenosis (p < 0.005). Spiral CT is more sensitive than FS in the recognition of hemodynamic relevant stenoses using the detection of coronary artery calcifications. Statistical parameters are comparable to ultrafast-CT. Spiral CT is a suitable non-invasive diagnostic technique in coronary heart disease. Coronary calcifications found incidentally in symptomatic patients at chest CT should be reported to the referring physician for further cardiological workup.