Performance of cone-beam computed tomography and multidetector computed tomography in diagnostic imaging of the midface: A comparative study on Phantom and cadaver head scans.

PURPOSE: To compare multidetector computed tomography (MDCT) and cone-beam computed tomography (CBCT) regarding radiation, resolution, image noise, and image quality. METHODS: CBCT and 256-MDCT were compared based on three scan protocols: Standard-dose (≈24 mGy), reduced-dose (≈9 mGy), and low-dose (≈4 mGy). MDCT images were acquired in standard- and high-resolution mode (HR-MDCT) and reconstructed using filtered back projection (FBP) and iterative reconstruction (IR). Spatial resolution in linepairs (lp) and objective image noise (OIN) were assessed using dedicated phantoms. Image quality was assessed in scans of 25 cadaver heads using a Likert scale. RESULTS: OIN was markedly higher in FBP-MDCT when compared to CBCT. IR lowered the OIN to comparable values in standard-mode MDCT only. CBCT provided a resolution of 13 lp/cm at standard-dose and 11 lp/cm at reduced-dose vs. 11 lp/cm and 10 lp/cm in HR-MDCT. Resolution of 10 lp/cm was observed for both devices using low-dose settings. Quality scores of MDCT and CBCT did not differ at standard-dose (CBCT, 3.4; MDCT, 3.3-3.5; p > 0.05). Using reduced- and low-dose protocols, CBCT was superior (reduced-dose, 3.2 vs. 2.8; low dose, 3.0 vs. 2.3; p < 0.001). CONCLUSION: Using the low-dose protocol, the assessed CBCT provided better objective and subjective image quality and equality in resolution. Similar image quality, but better resolution using CBCT was observed at higher exposure settings. KEY POINTS: • The assessed CBCT device provided better image quality at lower doses. • Objective and subjective image quality were comparable using higher exposure settings. • CBCT showed superior spatial resolution in standard-dose and reduced-dose settings. • Modern noise-reducing tools are used in CBCT devices currently. • MDCT should be preferred for assessment of soft-tissue injuries and oncologic imaging.

Quantification of radiation dose savings in cardiac computed tomography using prospectively triggered mode and ECG pulsing: a phantom study.

OBJECTIVE: To quantify radiation dose reduction in cardiac computed tomography (CT) using a prospectively triggered mode compared with a retrospective ECG-gated helical mode. METHODS: Absorbed organ doses in cardiac 64-row multidetector CT were quantified using an anthropomorphic male Alderson phantom with 74 thermoluminescence dosimeters. Three different imaging protocols were applied: retrospective ECG-gating, retrospective ECG-gating with additional ECG-pulsing, and a prospectively triggered mode. The measured organ doses were compared with dose estimation by a mathematical phantom. RESULTS: Compared with the retrospective ECG-gating mode, the mean relative organ doses were reduced by 44% using ECG pulsing and by 76% using the prospectively triggered mode. The range of dose savings varied from 34% to 49% using ECG pulsing and from 65% to 87% using the prospectively triggered mode. The effective dose was 16.5 mSv using retrospective gating, 9.2 mSv using retrospective gating with ECG pulsing and 4.0 mSv using the prospectively triggered mode. CONCLUSIONS: Our measurements confirm the high dose-saving potential of the prospectively triggered technique in cardiac CT. The reduction in the organ doses measured corresponds to estimates determined by the mathematical phantom. The effective dose calculated by the mathematical phantom was, in some cases, significantly lower than that calculated using the anthropomorphic phantom.

Simulated low-dose computed tomography in oncological patients: a feasibility study.

OBJECTIVE: Image quality of chest and abdominal computed tomographic (CT) scans was evaluated at different doses to assess the lowest value of x-ray dose at which the image quality was not being affected. MATERIALS AND METHODS: Using multislice CT (MSCT), 29 patients who submitted to follow-up examinations were examined using a combined MSCT protocol of the chest and the abdomen on 4-raw MSCT (Siemens, Erlangen, Germany). For each examination, approximately 120 mL of contrast agent (Bracco-Altana, Konstanz, Germany) was applied intravenously. The raw data were transferred to an external personal computer equipped with an image reconstruction software (CardioRecon 6; Siemens, Forchheim, Germany) to simulate 5 different dose levels. To simulate them correctly, a milliampere second-dependent noise was added to every image, so that the changes in a current-time product could be imitated. The images were compared in consensus by 2 radiologists who were not informed about the technical scanning parameters, that is, dose parameters, and were graded in 4 different subcategories on a 1-to-5-point scale. For statistical analysis, the Friedman test was used. Additional evaluations for lesions smaller than 1.0 cm were performed and analyzed separately. RESULTS: For image noise, there was a significant change between 40 and 60 mA s. For lesion detection, there was no significant change. The contour of the small objects did not differ between 90, 60, and 40 mA s. However, a dose reduction to 30 mA s had a significant effect. The contrast did not differ between 90, 60, 40, and even down to 30 mA s. Only a maximal dose reduction to 20 mA s had a significant effect on the contrast. The level of noise was most sensitive to the current. Whereas a dose reduction to 60 mA s did not yet have a significant effect, there was a significant increase of noise at 40 mA s. CONCLUSIONS: The MSCT can be applied with a lower dose than that usually selected in examinations at present to follow-up and stage the oncological patients adequately.

Sacroplasty in a cadaveric trial: comparison of CT and fluoroscopic guidance with and without balloon assistance.

Sacral insufficiency fractures can cause severe, debilitating pain to patients concerned. The incidence of this fracture type correlates with the appearance of osteoporosis in the elderly population. A polymethylmethacrylate (PMMA) cement injection procedure called sacroplasty has been recently described as an optional method for the treatment of this fracture type. However, the correct cement placement in the complex anatomical structure of the sacrum is a surgical challenge. The aim of the study is to compare the precision, safety, and radiation exposure of standard multiplanar fluoroscopy and computed tomography (CT) guidance for PMMA application to the sacrum using both balloon-assisted sacroplasty and conventional sacroplasty. A controlled experimental investigation in a human cadaver trial has been performed. Two imaging and two application modalities to monitor percutaneous PMMA injection to the sacrum were examined. The application forms were randomized from side to side of the pelvis. We found less cement extravasation in the CT-guided groups, but also a significant higher radiation exposure (P < 0.05) by using CT guidance. The conventional fluoroscopy-guided sacroplasty revealed the shortest procedure time (incision to closure time) of all treatment groups (P < 0.01). These findings show no difference regarding cement extravasation between ballon-assisted and conventional sacroplasty. Further, in comparison to fluoroscopy-assisted technique, the CT-guided cement injection seems to decrease the risk of cement extravasation, irrespective of the use of an additional balloon assistance. However, we have to consider a greater radiation exposure using CT guidance. Further investigations will proof the suitability in the normal course of clinical life.

[Integration of cardiac computed tomography into pulmonary vein isolation in patients with paroxysmal atrial fibrillation]. / Integration einer präinterventionellen Computertomografie des Herzens in die therapeutische Pulmonalvenenisolation bei Patienten mit paroxysmalem Vorhofflimmern.

PURPOSE: Detailed anatomic information of the left atrium is necessary for securely performing radiofrequency ablation of atrial fibrillation-triggering ectopies in the pulmonary vein ostia. In this study the impact of a preinterventionally acquired cardiac computed tomography (CT) on pulmonary vein isolation (PVI) was assessed. MATERIALS AND METHODS: Examinations of 54 patients with paroxysmal atrial fibrillation undergoing PVI were analyzed. In 27 patients a supplementary cardiac CT was obtained prior to PVI (CT group, 12 women, 15 men, 59.7+/-9.9 years of age): 16 x 1.5 mm collimation, 0.2 pitch, 120 kV tube voltage, 400 effective mAs. The fluoroscopy time, effective dose and quantity of radiofrequency (RF) pulses of the following catheter ablation were compared to 27 patients undergoing stand-alone PVI (11 women, 16 men, 62.0+/-9.9 years of age). Mann-Whitney tests served for statistical comparison. RESULTS: CT datasets were successfully integrated into the ablation procedure of each patient in the CT group. The mean quantity of RF pulses was significantly lower in the CT group (22.1+/-8.0 vs. 29.1+/-11.9, p=0.030), and a significant reduction of fluoroscopy time was found (41.8+/-12.0 min vs. 51.2+/-16.0 min, p=0.005). Effective doses of the catheter ablation differed in an equivalent dimension but altogether not significantly (14.9+/-10.0 mSv vs. 20.0+/-16.0 mSv, p=0.203). The mean additive effective dose of the cardiac CT was 8.5+/-0.3 mSv. CONCLUSION: CT-guided ablation of atrial fibrillation requires less fluoroscopy time than stand-alone PVI. Due to the multi-faceted dependency of individual fluoroscopy doses, a consistent reduction of the effective dose was not observed. Since supplementary CT constitutes an additive dose, optimized CT atriography needs to be designed in order to provide sufficient image quality while reducing X-ray exposure. The reduction in RF pulses implies an increase in the effectiveness and safety of catheter ablation.

[Image quality of thickened slabs in multislice CT chest examinations: postprocessing vs. direct reconstruction]. / Bildqualität aufaddierter Schichten bei MSCT-Untersuchungen des Thorax: Bildnachverarbeitung versus Direktrekonstruktion.

PURPOSE: Postprocessing offers the possibility of real-time creation of thickened slabs from a set of thin slices. This allows the interactive change from thick to thin slices for better evaluation of unclear lesions. As a result the clinical workflow of MSCT evaluation can be improved. However, to be able to apply this postprocessing software in the clinical routine, degradations in the image quality (compared to standard original reconstructed images) have to be avoided. The purpose of this study was to compare the image quality of thickened slabs from MSCT chest examinations that have either been directly reconstructed from the raw data or have been retrospectively generated via postprocessing. MATERIALS AND METHODS: Chest MSCT examinations of 20 patients (mean age: 56 years) were performed on a 16-slice MSCT scanner (Mx8000IDT16, Philips, Best, Netherlands) using the following scan parameters: 120 kV, 94 effective mAs, 16 x 1.5 mm collimation, 512 x 512 matrix, field of view 371 x 371 mm, CTDIvol = 6.3 mGy, DLP = 210 mGyxcm). Slices with a thickness of 3 and 5 mm were generated for each examination both directly from the raw data and via postprocessing. Corresponding images from postprocessing and direct reconstruction (lung/soft tissue window) were evaluated by two radiologists with respect to 5 criteria on the basis of a five-point scale: organ structure, contour of small objects, contrast, image noise and artifacts. Differences between both data sets regarding image quality were assessed for each of the 5 criteria using a Wilcoxon test with Bonferroni correction. In addition, image noise was analyzed quantitatively in a region of interest in the aorta. RESULTS: For the lung and soft tissue window, both reviewers and all criteria, no differences in image quality were detected between the thickened slices obtained via direct reconstruction and the postprocessing method. In 96 % and 95 % of the cases images of the two reconstruction methods were graded identically for 3 mm and 5 mm slices. In the remaining 4 % and 5 %, the evaluations differed only by one point on the five-point scale. The median grade of the first reviewer was 1 and that of the second reviewer was 2. There were no differences in the quantitative analysis of image noise between both methods. CONCLUSION: The interactive creation of thickened slices is an effective tool for the evaluation of MSCT examinations. For the defined scan parameters in this study there were no differences in image quality between postprocessing methods (e. g. slab viewer) and direct image reconstruction.

Limitations in the determination of total filtration of x-ray tube assemblies.

A brief introduction is given to various inferential methods for the determination of total filtration of x-ray tube assemblies. The HVL method, which is most commonly used, was investigated in detail. The influence of a number of parameters on the relationship between filtration and HVL was systematically studied. The results clearly show that the HVL method only provides a rough estimate for filtration with errors of typically +/- 30%. As a consequence, quality assurance checks on the acceptance and status test level must consider the limited accuracy of this method. Changing requirements from minimum filtration to minimum HVL permitted at particular kVp does not considerably improve the situation.

Aluminum equivalence of materials used in diagnostic radiology and its dependence on beam quality.

A semi-empirical theory has been derived that relates the aluminum equivalence of various materials used in diagnostic radiology to their attenuation coefficients. The dependence of the aluminum hardness (AHE) and attenuation (AAE) equivalent on the beam quality is described in terms of effective energy. This 'aluminum equivalence approach' (ALEAP) gives estimates of the aluminum equivalent, regardless of spectral shape, that are usually within +/- 5% except when absorption edges are involved. A reasonable definition for the AHE of K-edge filters is offered. Suggestions are made for methods of testing for compliance with standards and regulations.

[CT-expo--a novel program for dose evaluation in CT]. / CT-Expo - ein neuartiges Programm zur Dosisevaluierung in der CT.

CT-Expo is a novel MS Excel application for assessing the radiation doses delivered to patients undergoing CT examinations, based on computational methods that were used to analyze the data collected in the German survey on CT practice in 1999. The program enables the calculation of all dose quantities of practical value, such as axial dose free-in-air, weighted CTDI, dose-length product, effective dose and uterine dose. In contrast to existing programs for CT dose assessment, CT-Expo offers a number of unique features, such as gender-specific dose calculation for all age groups (adults, children, newborns), applicability to all existing scanner models including correction of scanner-specific influences, and the possibility of comparison with the results from the German CT survey on CT practice. Three different application modules offer free and standardized dose calculations as well as a comprehensive benchmarking section including guidance on dose optimization. The program is available as shareware in both German and English version. Additional information and a demo version free of charge can be requested via e-mail from the author's address stamm.georg@mh-hannover. de) or from the web page http://www.mh-hannover.de/kliniken/radiologie/str_04.html.

[Diagnostic imaging in polytrauma: comparison of radiation exposure from whole-body MSCT and conventional radiography with organ-specific CT]. / Radiologische Bildgebung beim Polytrauma: Dosisvergleich von Ganzkörper-MSCT und konventionellem Röntgen mit organspezifischer CT.

PURPOSE: To compare the radiation dose of whole-body multislice CT (MSCT) and conventional radiography with organ-specific CT in polytrauma. MATERIALS AND METHODS: The whole-body MSCT encompassing brain, neck and midface, chest, abdomen and pelvis was performed on a Somatom Volume Zoom (Siemens). Conventional radiography consisted of chest and cervical, thoracic and lumbar spine in two views as well as pelvis (Polymat, Siemens). Three combinations of organ specific CT were chosen: CT examination of (1) head and cervical spine, (2) head, cervical spine and chest, (3) head, cervical spine and abdomen. The effective doses of whole-body MSCT and conventional radiography with organ-specific CT were calculated. RESULTS: Effective doses were 20 mSv for whole-body MSCT, 2 mSv for conventional x-ray, and 5 mSv for combination (1), 8 mSv for combination (2) and (3) 16 mSv for combination (3) of the organ-specific CT. The ratio of radiation dose between whole-body MSCT and radiography was 10 : 1. This ratio was reduced to 3 : 1, 2 : 1 and 1 : 1 when a combination of radiography and CT was performed. CONCLUSIONS: Whole-body MSCT in polytrauma compared to conventional radiography with organ-specific CT induces a threefold increased dose in unfavorable situations and no increased dose in favorable situations. Nevertheless, routine use of whole-body MSCT should be critically evaluated and should be adapted to the clinical benefit.

[Optimization of beam filtering, kv-ma regulation curve and image intensifier entrance exposure rate to reduce radiation exposure in angiographic fluoroscopy]. / Optimierung von Zusatzfilterung, Durchleuchtungskennlinie und Bildverstärker-Eingangsdosisleistung zur Reduktion der Strahlenexposition bei der Angiographie.

AIM OF STUDY: Evaluation of radiation exposure and image quality during fluoroscopy using a new vascular X-ray system. MATERIAL AND METHODS: The measurements were made on an Integris V 3000 X-ray system with MRC tube and SpectraBeam technology (Philips Medical Systems, Hamburg). Entrance dose rates were measured with phantoms for the three fluoroscopy levels (1-3) which differed with regard to beam filtering and image intensiver entrance exposure rate. We evaluated 132 diagnostic and interventional angiographic studies. The angiographic investigators were asked to start with level 1 and to change to the next fluoroscopy level only in the case of insufficient image quality. RESULTS: Entrance dose rate is reduced by approx. 74% at fluoroscopy level 1 and by approx. 46% at level 2 relative to level 3 which is comparable to angiographic X-ray systems without MRC tube and SpectraBeam technology. Because level 1 ensured a sufficient image quality in 92% of the diagnostic and 60% of the interventional angiographic procedures a change to higher fluoroscopy levels was not necessary. CONCLUSION: Reduction of the intensifier exposure rate and the optimization of beam filtering enabled us to reduce the radiation exposure considerably. The procedure was well accepted by the angiographic investigators due to the diagnostically sufficient image quality of the fluoroscopy level 1.

[Image quality of thin- and thick-slice MSCT reconstructions in low-contrast objects (liver lesions) with equal doses]. / Dünn- und dickschichtige MSCT-Untersuchungen bei Niedrigkontrastobjekten (Leberläsionen): Vergleich der Bildqualität bei gleicher Dosis.

PURPOSE: To evaluate the image quality of thin-section MSCT examinations of low-contrast objects such as liver lesions, and to find out whether a thin slice technique requires an increase in radiation dose. MATERIALS AND METHODS: MSCT examinations of the liver were performed in the portal venous phase on a Volume Zoom Scanner (Siemens, Erlangen) with a collimation of 4 x 2.5 mm, 120 kV, 125 mAs and table speed of 12.5 mm. Forty small hypodense liver lesions with a mean size of 3 mm (1 to 8 mm) were reconstructed using a slice thickness of 3, 5, 7, and 10 mm. All lesions were evaluated for each slice thickness by 3 independent radiologists using a 5-point scale (excellent to poor) for the following 7 criteria: contrast, demarcation and contour of the lesion, image noise and quality, demarcation of liver veins and liver contour. The mean values of the reviewers' scores were calculated. The correlation of the three observers in the evaluation of the criteria was determined using the Kendall's Tau coefficient. RESULTS: The 3-mm thin sections were excellent in the evaluation of lesion detection, lesion contrast and lesion contour with a mean score of 1.4 compared to 4.1 for 10-mm sections. Concerning the criteria image quality and liver contour, thin sections achieved the best results in our series. Image noise was pronounced in thin sections but did not affect negatively the image analysis. Interrater agreement was 0.53 for the criterium image noise. CONCLUSION: Thin sections in MSCT examinations of low contrast objects such as liver lesions do not require an increase in radiation dose because the increase in image noise is compensated by improved lesion contrast.

[5 years of "concerted action dose reduction in CT" -- what has been achieved and what remains to be done?]. / 5 Jahre Konzertierte Aktion Dosisreduktion CT--was wurde erreicht, was ist noch zu tun?

In May 1998, the German "Concerted Action Dose Reduction in CT" was founded by all parties involved in CT. Its intention was to achieve a significant reduction of the radiation exposure caused by CT, a matter that has increasingly been considered a major challenge since the early nineties. As a result of a number of joint efforts, the essential preconditions have been established by now. The fifth anniversary of the Concerted Action gave rise for both retrospection and outlook on the tasks that have already been accomplished and those that still need to be done. For this purpose, a one-day symposium took place in Berlin on November 4, 2003. The contents of a total of 18 contributions will be outlined here in brief.

Derivation and mapping of critical loads for nitrogen and trends in their exceedance in Germany.

The term "critical load" means a quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur, according to present knowledge. In the case of nitrogen, both oxidised and reduced compounds contribute to the total deposition of acidity, which exceeds critical loads in many forest ecosystems. These also cause negative effects through eutrophication. Critical loads of nitrogen were derived for forest soils (deciduous and coniferous forest), natural grassland, acid fens, heathland, and mesotrophic peat bogs. In Germany, a decrease in sulphur emissions over the past 15 years resulted in a reduced exceedance of critical loads for acid deposition. In the same period it was noted that reduction in the emissions of nitrogen oxides and ammonia remained insignificant. Therefore, emissions of nitrogen compounds have become relatively more important and will continue to threaten ecosystem function and stability. The risk of environmental damage remains at an unacceptable level. The German maps show the degree to which the critical loads are exceeded, and they present current developments and an expected future trend. Results indicate that recovery from pollutant stress occurs only gradually.

Impact of increasing levels of advanced iterative reconstruction on image quality in low-dose cardiac CT angiography.

PURPOSE: To investigate the effects of an advanced iterative reconstruction (IR) technique on subjective and objective image quality (IQ) in low-dose cardiac CT angiography (CCTA). MATERIALS AND METHODS: 30 datasets of prospectively triggered "step-and-shoot" CCTA scans acquired on a 256-slice CT scanner with optimized exposure settings were processed on a prototype IR system using filtered back-projection (FBP) and 4 levels of advanced IR (iDose4, Philips) providing incremental rates of IR (level 2, 4, 6, 7). In addition, the effects of different reconstruction kernels (semi-smooth [CB], standard with edge-enhancement [XCB]) and a "multi-resolution" feature [MR] to preserve the noise power spectrum were evaluated resulting in a total of n = 480 image sets. Contrast-to-noise ratios (CNR) were computed from regions of interest at 9 coronary locations. The subjective IQ was rated on a 4-point-scale with "classic" image appearance and noise-related artifacts as main criteria. RESULTS: At an effective dose of 1.7 ±â€Š0.7 mSv, the CNR significantly improved with every increasing level of IR (range: 14.2 - 27.8; p < 0.001) with the best objective IQ at the highest level of IR (level 7). The subjective IQ, however, was rated best at the medium level of IR (level 4) with minimal artifacts and a more "classic" image appearance when compared to higher IR levels. The XCB kernel provided better subjective ratings than CB (p < 0.05) and the MR feature further increased the IQ at a high level of IR. CONCLUSION: The objective IQ of low-dose CCTA progressively improves with an increasing level of IR. The best subjective IQ, however, is reached at medium levels of IR combined with an edge-enhancing kernel allowing for preservation of a "classic" image appearance suggesting application in the clinical routine. KEY POINTS: • iterative reconstruction (IR) improves image quality in low-dose coronary CTA• objective image quality (CNR) enhances with increasing level of IR• best subjective image quality is reached at medium level of IR• "multi-resolution" algorithm further improves image quality at a higher level of IR.

Intraindividual evaluation of the influence of iterative reconstruction and filter kernel on subjective and objective image quality in computed tomography of the brain.

OBJECTIVES: To intraindividually evaluate the potential of 4th generation iterative reconstruction (IR) on brain CT with regard to subjective and objective image quality. METHODS: 31 consecutive raw data sets of clinical routine native sequential brain CT scans were reconstructed with IR level 0 (= filtered back projection), 1, 3 and 4; 3 different brain filter kernels (smooth/standard/sharp) were applied respectively. Five independent radiologists with different levels of experience performed subjective image rating. Detailed ROI analysis of image contrast and noise was performed. Statistical analysis was carried out by applying a random intercept model. RESULTS: Subjective scores for the smooth and the standard kernels were best at low IR levels, but both, in particular the smooth kernel, scored inferior with an increasing IR level. The sharp kernel scored lowest at IR 0, while the scores substantially increased at high IR levels, reaching significantly best scores at IR 4. Objective measurements revealed an overall increase in contrast-to-noise ratio at higher IR levels, which was highest when applying the soft filter kernel. The absolute grey-white contrast decreased with an increasing IR level and was highest when applying the sharp filter kernel. All subjective effects were independent of the raters' experience and the patients' age and sex. CONCLUSION: Different combinations of IR level and filter kernel substantially influence subjective and objective image quality of brain CT.

Performance of an automatic dose control system for CT: patient studies.

PURPOSE: To study the effect of an automatic dose control (ADC) system with adequate noise characteristic on the individual perception of image noise and diagnostic acceptance compared to objectively measured image noise and the dose reductions achieved in a representative group of patients. MATERIALS AND METHODS: In a retrospective study two matched cohorts of 20 patients each were identified: a manual cohort with exposure settings according to body size (small - regular - large) and an ADC cohort with exposure settings calculated by the ADC system (DoseRight 2.0™, Philips Healthcare). For each patient, 12 images from 6 defined anatomic levels from contrast-enhanced scans of chest and abdomen/pelvis were analyzed by 4 independent readers concerning image noise and diagnostic acceptance on a five-point Likert scale and evaluated for objectively measured image noise. Radiation exposure was calculated from recorded exposure data. RESULTS: Use of the ADC system reduced the average effective dose for patients by 36 % in chest scans (3.2 vs. 4.9 mSv) and by 17 % in abdomen/pelvis scans (7.6 vs. 8.3 mSv). Average objective noise was slightly lower in the manual cohort (11.1 vs. 12.8 HU), correlating with a slightly better rating in subjective noise score (4.4 vs. 4.2). However, diagnostic acceptance was rated almost equal in both cohorts with excellent image quality (4.6 vs. 4.5). CONCLUSION: Use of an ADC system with adequate noise characteristic leads to significant reductions in radiation exposure for patients while maintaining excellent image quality.

Impact of a 4th generation iterative reconstruction technique on image quality in low-dose computed tomography of the chest in immunocompromised patients.

PURPOSE: To determine the image quality of an iterative reconstruction (IR) technique in low-dose MDCT (LDCT) of the chest of immunocompromised patients in an intraindividual comparison to filtered back projection (FBP) and to evaluate the dose reduction capability. MATERIALS AND METHODS: 30 chest LDCT scans were performed in immunocompromised patients (Brilliance iCT; 20-40 mAs; mean CTDIvol: 1.7 mGy). The raw data were reconstructed using FBP and the IR technique (iDose4™, Philips, Best, The Netherlands) set to seven iteration levels. 30 routine-dose MDCT (RDCT) reconstructed with FBP served as controls (mean exposure: 116 mAs; mean CDTIvol: 7.6 mGy). Three blinded radiologists scored subjective image quality and lesion conspicuity. Quantitative parameters including CT attenuation and objective image noise (OIN) were determined. RESULTS: In LDCT high iDose4™ levels lead to a significant decrease in OIN (FBP vs. iDose7: subscapular muscle 139.4 vs. 40.6 HU). The high iDose4™ levels provided significant improvements in image quality and artifact and noise reduction compared to LDCT FBP images. The conspicuity of subtle lesions was limited in LDCT FBP images. It significantly improved with high iDose4™ levels (> iDose4). LDCT with iDose4™ level 6 was determined to be of equivalent image quality as RDCT with FBP. CONCLUSION: iDose4™ substantially improves image quality and lesion conspicuity and reduces noise in low-dose chest CT. Compared to RDCT, high iDose4™ levels provide equivalent image quality in LDCT, hence suggesting a potential dose reduction of almost 80%.

Performance of an automatic dose control system for CT: specifications and basic phantom tests.

PURPOSE: To assess the performance and to provide more detailed insight into the characteristics and limitations of devices for automatic dose control (ADC) in CT. MATERIALS AND METHODS: A comprehensive study on DoseRight 2.0, the ADC system provided by Philips for its Brilliance CT scanners, was conducted. Phantom tests were carried out on a 64-slice scanner (Brilliance 64) using assorted quality control (QC) phantoms that allowed verification of the basic specifications. If feasible, the findings were verified by model calculations based on known specifications. RESULTS: For all tests, the dose reductions and modulation characteristics fully met the values expected from the specifications. Adverse effects due to increased image noise were only moderate as a result of the "adequate noise system" design that employs comparatively gentle modulation, and the additional use of adaptive filtration. CONCLUSION: Simple tests with QC phantoms allow evaluation of the most relevant characteristics of devices for ADC in CT.