Laryngectomy plus postoperative radio(system)therapy versus primary radio(system) therapy for the treatment of locally advanced laryngeal and hypopharyngeal cancer - results from the University Clinical Cancer Registry Regensburg.

BACKGROUND: There are few adequate randomized clinical trials directly comparing the therapeutic options of primary laryngectomy (pLE) vs. primary radio(system)therapy (pR(S)T) in patients with locally advanced laryngeal and hypopharyngeal carcinoma and thus little clear scientific evidence to decide which patients will benefit most from which procedure. AIMS/OBJECTIVES: Aim was to compare survival between the therapeutic options and to learn from the limitations of this study, especially in the context of improved clinical assessment. MATERIAL AND METHODS: The clinical data of patients treated between January 2010 and February 2022 were obtained from the electronic database of the University Hospital Regensburg. Overall survival (OS) and progression-free survival (PFS) were compared between the treatment groups. RESULTS: The study included 193 patients (pLE n = 68, pR(S)T, n = 125). Median OS was 31.2 months and median PFS was 24.7 months with no significant difference between the treatment groups (p > .050). Patients who did not receive complete treatment as recommended by the tumor conference (n = 47, 24.4%) had a higher risk of death (p = .024). CONCLUSIONS AND SIGNIFICANCE: The results of our study are consistent with the survival data reported in the literature. More detailed systematic data in clinical routine (e.g. relevant comorbidities) are required to ensure guideline-based recommended therapy.

Dose reduction in pediatric computed tomography with automated exposure control.

RATIONALE AND OBJECTIVES: Since the introduction of computed tomographic (CT) imaging in the 1970s, the number of examinations has increased steadily. CT imaging is an essential part of routine workup in diagnostic radiology. The great advantage of multidetector computed tomography is the acquisition of a large amount of data in a short time period, thus speeding up diagnostic procedures. To protect patients from unnecessary radiation exposure, different approaches have been developed. In this study, the efficacy of automated exposure control (AEC) software in multidetector CT imaging with a focus on dose reduction in pediatric examinations was assessed. MATERIALS AND METHODS: Between August 2004 and September 2005, a total of 71 children (40 male, 31 female; age range, 2-13 years; mean age, 7.2 years) were examined using a multisource CT scanner. Three different regions (chest, upper abdomen, and pelvis) were examined. Overall image quality was assessed with a subjective scale (1 = excellent, 2 = diagnostic, 3 = nondiagnostic). For all examinations, AEC was used. From the scanner's patient protocol, dose-length product, volume CT dose index, and tube current-time product were calculated for each examination. RESULTS: With AEC, a mean dose reduction of 30.6% was calculated. Images were rated as excellent (n = 39) or diagnostic (n = 32). Nondiagnostic image quality was not seen. Dose-length product and volume CT dose index were reduced by 30.4% and 29.5%, respectively. Overall, a mean dose reduction of 30.1% of the effective dose (5.8 ± 3.1 vs 8.4 ± 4.6 mSv) was achieved (P < .001). CONCLUSIONS: With AEC software, a mean dose reduction of 30% without any loss in diagnostic image quality is possible.

Effect of nonlinear three-dimensional optimized reconstruction algorithm filter on image quality and radiation dose: validation on phantoms.

A new technique called the nonlinear three-dimensional optimized reconstruction algorithm filter (3D ORA filter) is currently used to improve CT image quality and reduce radiation dose. This technical note describes the comparison of image noise, slice sensitivity profile (SSP), contrast-to-noise ratio, and modulation transfer function (MTF) on phantom images processed with and without the 3D ORA filter, and the effect of the 3D ORA filter on CT images at a reduced dose. For CT head scans the noise reduction was up to 54% with typical bone reconstruction algorithms (H70) and a 0.6 mm slice thickness; for liver CT scans the noise reduction was up to 30% with typical high-resolution reconstruction algorithms (B70) and a 0.6 mm slice thickness. MTF and SSP did not change significantly with the application of 3D ORA filtering (P > 0.05), whereas noise was reduced (P < 0.05). The low contrast detectability and MTF of images obtained at a reduced dose and filtered by the 3D ORA were equivalent to those of standard dose CT images; there was no significant difference in image noise of scans taken at a reduced dose, filtered using 3D ORA and standard dose CT (P > 0.05). The 3D ORA filter shows good potential for reducing image noise without affecting image quality attributes such as sharpness. By applying this approach, the same image quality can be achieved whilst gaining a marked dose reduction.

Dose reduction during CT fluoroscopy: phantom study of angular beam modulation.

PURPOSE: To prospectively evaluate, in a phantom, the dose reductions achievable by using angular beam modulation (ABM) during computed tomographic (CT) fluoroscopy-guided thoracic interventions. MATERIALS AND METHODS: To enable measurement of organ doses and effective patient dose, a female Alderson-Rando phantom was equipped with thermoluminescent dosimeters (TLDs) in 41 positions, with three TLDs in each position. Additionally, the local dose was assessed in 22 locations above the phantom to estimate the radiation exposure to the radiologist's hand and the patient's skin dose during thoracic interventions. Radiation exposure was performed with a 64-section multidetector CT scanner in the CT fluoroscopy mode, simulating a CT fluoroscopy-guided chest intervention. Effective dose, breast dose, and the dose to the radiologist's hand during the simulated chest intervention were measured with and without ABM. Image noise as an indicator for image quality was compared for both settings. Statistical significance of the measured dose reductions and the image noise was tested by using the paired-samples t test, with P < .05 indicating a significant difference. RESULTS: ABM significantly reduced the effective patient dose by 35%, the skin dose by 75%, the breast dose by 47% (P < .001 for all), and the physician's hand dose by between 27% (scattered radiation, P = .007) and 72% (direct radiation, P < .001). No significant difference was found in a comparison of the image noise with and that without ABM. CONCLUSION: ABM leads to significant dose reductions for both patients and personnel during CT fluoroscopy-guided thoracic interventions, without impairing image quality.

The influence of heart rate, slice thickness, and calcification density on calcium scores using 64-slice multidetector computed tomography: a systematic phantom study.

OBJECTIVE: The purpose of this study was to investigate the influence of heart rate, slice thickness, and calcification density on absolute value and variability of calcium score using 64-slice multidetector computed tomography (MDCT). METHODS AND MATERIALS: Three artificial arteries containing each 3 lesions with varying density were scanned using a moving cardiac phantom at rest and at 50 to 110 beats per minute (bpm) at 10-bpm intervals on a 64-slice MDCT. Images were reconstructed at slice thicknesses (increment) of 0.6 (0.4), 0.75 (0.5), 1.5 (1.5), and 3.0 (3.0) mm. The amount of calcium was expressed as an Agatston score, volume score, and equivalent mass. RESULTS: Absolute coronary artery calcium (CAC) scores decreased [average -37% for low density calcification (LDC)] or increased [average +32% for high density calcification (HDC)] at heart rates over 60 bpm depending on slice thickness and scoring method. Thinner slice thicknesses yielded higher CAC scores. Variability of the CAC scores increased with increasing heart rates especially for low density calcifications (8% at rest vs. 50% at 110 bpm). Variability also increased for thicker slices (average 6% for 0.6 mm vs. 18% for 3.0 mm). Variability was lower for HDC compared with LDC (approximately 5% for HDC vs. 27% for LDC at 70 bpm, averaged over all methods and slice thicknesses). CONCLUSION: CAC-scoring is strongly influenced by cardiac motion, calcification density, and slice thickness. CAC scores increase for high density calcifications and decrease for low density calcifications at increasing heart rates. Heart rate should be reduced on 64-slice MDCT to obtain a lower degree of variability of CAC-scoring, preferably below 70 bpm. A thinner slice thickness further enhances the reproducibility.

Dual-source computed tomography for assessing cardiac function: a phantom study.

PURPOSE: To investigate the influence of heart rate and temporal resolution on the assessment of global ventricular function with dual-source computed tomography (DSCT). MATERIALS AND METHODS: A dynamic cardiac phantom was repeatedly scanned with a DSCT scanner applying a standardized scan protocol at different heart rates, ranging from 40 to 140 bpm. Images were reconstructed with monosegmental and bisegmental algorithms using data from a single source and from both sources. Ventricular volumes and ejection fraction (EF) were computed by semiautomated analysis. Results were compared with the phantom's real volumes. Interscan, intraobserver, and interobserver variability were calculated. RESULTS: For single-source data reconstruction temporal resolution was fixed to 165 milliseconds, whereas dual-source image reconstructions resulted in a temporal resolution of 83 milliseconds (monosegmental) and 67.7+/-14.2 milliseconds (bisegmental), respectively. In general, deviation from the phantom's real volumes was less with dual-source data reconstruction when compared with single-source data reconstruction. Comparing dual-source data reconstruction with single-source data reconstruction, the percent deviation from the phantom's real volumes for EF was 0.7% (monosegmental), 0.7% (bisegmental), and 4.3% (single source), respectively. There was no correlation between heart rate and EF for dual-source data reconstruction (r=-0.168; r=-0.157), whereas a relevant correlation was observed for single-source data reconstruction (r=-0.844). Interscan, intraobserver, and interobserver variability for EF were 1.4%, 0.9%, and 0.3%, respectively. CONCLUSIONS: DSCT allows reliable quantification of global ventricular function independent of the heart rate. Multisegmental image reconstruction is not needed for DSCT assessment of global ventricular function.

Dose performance of a 64-channel dual-source CT scanner.

PURPOSE: To prospectively compare the dose performance of a 64-channel multi-detector row computed tomographic (CT) scanner and a 64-channel dual-source CT scanner from the same manufacturer. MATERIALS AND METHODS: To minimize dose in the cardiac (dual-source) mode, the evaluated dual-source CT system uses a cardiac beam-shaping filter, three-dimensional adaptive noise reduction, heart rate-dependent pitch, and electrocardiographically based modulation of the tube current. Weighted CT dose index per 100 mAs was measured for the head, body, and cardiac beam-shaping filters. Kerma-length product was measured in the spiral cardiac mode at four pitch values and three electrocardiographic modulation temporal windows. Noise was measured in an anthropomorphic phantom. Data were compared with data from a 64-channel multi-detector row CT scanner. RESULTS: For the multi-detector row and dual-source CT systems, respectively, weighted CT dose index per 100 mAs was 14.2 and 12.2 mGy (head CT), 6.8 and 6.4 mGy (body CT), and 6.8 and 5.3 mGy (cardiac CT). In the spiral cardiac mode (no electrocardiographically based tube current modulation, 0.2 pitch), equivalent noise occurred at volume CT dose index values of 23.7 and 35.0 mGy (coronary artery calcium CT) and 58.9 and 61.2 mGy (coronary CT angiography) for multi-detector row CT and dual-source CT, respectively. The use of heart rate-dependent pitch values reduced volume CT dose index to 46.2 mGy (0.265 pitch), 34.0 mGy (0.36 pitch), and 26.6 mGy (0.46 pitch) compared with 61.2 mGy for 0.2 pitch. The use of electrocardiographically based tube current-modulation and temporal windows of 110, 210, and 310 msec further reduced volume CT dose index to 9.1-25.1 mGy, dependent on the heart rate. CONCLUSION: For electrocardiographically gated coronary CT angiography, image noise equivalent to that of multi-detector row CT can be achieved with dual-source CT at doses comparable to or up to a factor of two lower than the doses at multi-detector row CT, depending on heart rate of the patient.

Evaluation of automated attenuation-based tube current adaptation for coronary calcium scoring in MDCT in a cohort of 262 patients.

The aim of our study was to evaluate attenuation-based tube current adaptation in coronary calcium scoring using ECG-gated multi-detector-row CT (MDCT). A total of 262 patients underwent non-enhanced cardiac MDCT. Group 1 was scanned using a standard protocol with 120 kV and 150 mAs(eff). Groups 2-4 were scanned using an attenuation-based dose-adaptation template (CARE Dose) with different effective reference mAs settings (150, 180, 210 mAs(eff)). Body-mass index (BMI) and CT-dose index values were calculated for each patient. Image noise and subjective image quality were assessed. Regression analysis was performed, and the variation coefficient of image noise was determined. Compared to the standard scan protocol a dose reduction of 31.1% for group 2 and 20.1% for group 3 was observed. Measurement variation of image noise was smaller for the attenuation-based dose adaptation protocols (group 2-4) (16.2-17.1%) compared to the standard scan protocol (32.3%). Regression analysis of groups 2-4 showed better correlation with improved dose usage based on BMI (all P

Influence of heart rate and temporal resolution on left-ventricular volumes in cardiac multislice spiral computed tomography: a phantom study.

PURPOSE: We sought to investigate the influence of heart rate and temporal resolution on the assessment of left-ventricular (LV) function with multislice spiral computed tomography (CT). MATERIAL AND METHODS: A dynamic cardiac phantom was repeatedly scanned with a 64-slice CT scanner using a standardized scan protocol (64 x 0.6 mm, 120kV, 770mAs(eff), 330 milliseconds rotation time) at different simulated heart rates, ranging from 40 to 140 beats per minute. Images were reconstructed with an algorithm utilizing data from 1 to 4 cardiac cycles (RR intervals). Ejection fraction (EF), end-systolic, end-diastolic, and stroke volume as well as cardiac output were calculated. Results of the measurements were compared with the real volumes of the phantom. Interscan and intraobserver variability were calculated. RESULTS: Using a monosegmental reconstruction algorithm, the temporal resolution was fixed to 165 milliseconds. With bi-, tri-, and quad-segmental image reconstruction, mean temporal resolution was 128.3 +/- 33.2 milliseconds, 103.3 +/- 49.2 milliseconds, and 87.8 +/- 81.5 milliseconds, respectively. Multisegmental image reconstruction resulted in a lower deviation when comparing measured and real volumes. Using mono-, bi-, tri-, and quad-segmental image reconstruction, the percent deviation between measured and real values for EF was 8.2%, 4.5%, 3.3%, and 3.4%, respectively. Applying multisegmental image reconstruction with improved temporal resolution the deviation decreased with increasing heart rate when compared with mono-segmental image reconstruction. Interscan and intraobserver variability for EF were 1.1% and 1.9%, respectively. CONCLUSION: Enhanced temporal resolution improves the quantification of LV volumes in cardiac multislice spiral CT, enabling reliable assessment of LV volumes even at increased heart rates.

Ultra-high resolution flat-panel volume CT: fundamental principles, design architecture, and system characterization.

Digital flat-panel-based volume CT (VCT) represents a unique design capable of ultra-high spatial resolution, direct volumetric imaging, and dynamic CT scanning. This innovation, when fully developed, has the promise of opening a unique window on human anatomy and physiology. For example, the volumetric coverage offered by this technology enables us to observe the perfusion of an entire organ, such as the brain, liver, or kidney, tomographically (e.g., after a transplant or ischemic event). By virtue of its higher resolution, one can directly visualize the trabecular structure of bone. This paper describes the basic design architecture of VCT. Three key technical challenges, viz., scatter correction, dynamic range extension, and temporal resolution improvement, must be addressed for successful implementation of a VCT scanner. How these issues are solved in a VCT prototype and the modifications necessary to enable ultra-high resolution volumetric scanning are described. The fundamental principles of scatter correction and dose reduction are illustrated with the help of an actual prototype. The image quality metrics of this prototype are characterized and compared with a multi-detector CT (MDCT).

Comparison of angular and combined automatic tube current modulation techniques with constant tube current CT of the abdomen and pelvis.

OBJECTIVE: The objective of our study was to compare image quality and radiation dose associated with abdominopelvic CT using combined modulation, angular modulation, and constant tube current. CONCLUSION: Compared with using a constant tube current to scan the abdomen and pelvis, the use of a combined modulation technique results in a substantial reduction (42-44%) in radiation dose with acceptable image noise and diagnostic acceptability.

Multi-detector row CT pulmonary angiography: comparison of standard-dose and simulated low-dose techniques.

PURPOSE: To compare standard-dose and simulated low-dose multi-detector row computed tomography (CT) pulmonary angiography. MATERIALS AND METHODS: The institutional review board approved the study protocol and waived patient informed consent because the study was based on existing data. Raw data from 21 CT scans obtained at 90 mAs (effective) in 11 women and 10 men aged 25-74 years (mean, 52 years) that showed at least one filling defect within a pulmonary artery were used to simulate CT pulmonary angiography with reduced radiation doses, at 60, 40, 20, and 10 mAs. Three independent readers coded each central and segmental pulmonary artery twice as positive, negative, or inconclusive for presence of a filling defect. The second reading of images obtained with 90 mAs was considered the reference standard. The potential dependence of results on reader, radiation dose, and/or pulmonary artery segment was investigated with analysis of variance. Positive and negative consistent values were calculated for standard-dose scans and simulated low-dose scans in the first reading session. The branching order of the artery with the most distal filling defect was recorded. The quality of intravascular contrast at each tube current-time product setting was scored on a five-point scale. Interreader agreement was investigated with kappa statistics. RESULTS: The frequencies of positive and inconclusive results (P = .21 and .08, respectively), positive and negative consistent values (P = .19 and .34, respectively), and branching order of the most distal artery with a filling defect (P = .41) did not depend on the radiation dose. Values for inter- and intrareader agreement were higher for central arterial segments than for branch arteries but were not influenced by dose reduction, regardless of arterial segment. The quality of intravascular contrast was not significantly changed when the tube current-time product was reduced from 90 to 40 mAs (P = .10 to >.99). CONCLUSION: The evaluated parameters remained stable when tube current-time product was reduced from 90 (effective) to 10 (simulated) mAs at multi-detector row CT pulmonary angiography.

Metallic prosthesis: technique to avoid increase in CT radiation dose with automatic tube current modulation in a phantom and patients.

The institutional review board approved this Health Insurance Portability and Accountability Act-compliant study protocol, with waiver of informed consent. The purpose of the study was to retrospectively evaluate the combined automatic tube current modulation technique in patients with orthopedic metallic prostheses. Five hundred abdominal-pelvic computed tomographic (CT) studies performed with combined modulation technique were reviewed to identify nine patients with metallic prostheses (mean age, 66 years; range, 35-86 years; male-female ratio, 5:4). On the basis of age and transverse abdominal images, these patients were matched with nine others with no metallic prostheses (mean age, 56 years; range, 36-72 years; male-female ratio, 4:5) who were control patients. Images were graded for extent and severity of streak artifacts (grade 1, streak artifact present but not substantially compromising evaluation of adjacent structures; grade 2, streak artifact present and slightly compromising evaluation of adjacent structures; and grade 3, streak artifact present and severely compromising evaluation of adjacent structures). Student t test was performed for statistical analysis. There was no difference in mean effective tube current-time product between study and control patients (P > .49). With automatic tube current modulation, an increase in CT dose caused by metallic prostheses can be successfully avoided.

Dose reduction in multislice computed tomography.

OBJECTIVE: Evaluation of the attenuation-based on-line modulation of tube current on multislice computed tomography (CT) to explore the potential of this dose-saving technique. METHODS: Fifty-five patients with follow-up CT examinations were scanned without and with a CARE Dose (Siemens Medical Solutions, Erlangen, Germany). The applied dose, image noise, and subjective image quality were evaluated. The reduction in patient exposure was determined by obtaining the effective milliamperes per second for each reconstructed scan and the absolute dosage requirement for the whole scan. RESULTS: The dose reduction achieved by applying the attenuation-based on-line modulation of tube current was 29.4% +/- 3.1% (P=0.002) for all scans, 30.5% +/- 3.2% (P=0.002) for the thorax scans, 29.7% +/- 2.9% (P=0.002) for the abdomen scans, and 28.7% +/- 2.7% (P=0.003) for the thorax and abdomen scans together. No significant restrictions in image quality were observed. CONCLUSIONS: Remarkable dose reduction can be obtained using the attenuation-based on-line modulation of tube current on multislice CT without compromising image quality.

Radiation dose and image quality in pediatric CT: effect of technical factors and phantom size and shape.

PURPOSE: To evaluate effects of varying tube current and voltage on radiation dose, image noise, and image contrast with different phantom sizes and shapes. MATERIALS AND METHODS: Four round lucite phantoms with 8-32-cm diameters were scanned with multi-detector row computed tomography (CT) and 80-120 kVp. Radiation dose was based on CT dose index, image noise, and iodine contrast and measured with constant and variable tube currents that were age appropriate for each tube voltage. Radiation dose and image noise and contrast were compared in round and oval 24-cm phantoms. For various combinations of technical factors and phantom sizes and shapes, percentage differences were calculated for radiation dose and image noise and contrast. Associations between tube voltage and radiation dose, image noise, and image contrast in round and oval phantoms were determined by fitting second-degree polynomials to data. Differences in radiation dose and image noise and contrast, which were attributable to differences in tube voltage, were tested with paired t tests. RESULTS: With 165-mAs tube current, radiation doses with 140- and 80-kVp tube voltages were 103% ([41.9 mGy - 20.6 mGy]/20.6 mGy) and 58% ([10.2 mGy - 4.2 mGy]/10.1 mGy) higher in the 8-cm phantom than in the 32-cm phantom. When tube current was adapted for phantom size, radiation dose at 80 kVp in the 8-cm phantom was reduced by 82% ([10.1 mGy - 1.8 mGy]/10.1 mGy). In the 8-cm phantom, tube voltage was decreased from 120 to 80 kVp and tube current remained at 165 mAs, resulting in a 68% noise increase ([3.1 HU - 1.8 HU]/1.8 HU). With variable tube current, 80-kVp tube voltage in the 8-cm phantom led to a 138% noise increase ([7.3 HU - 3.1 HU]/3.1 HU). With reduced tube voltage, image contrast increased. In the 8-cm phantom, with a constant 165-mAs tube current and a decrease in tube voltage from 120 to 80 kVp, there was a 35% ([333 HU - 217 HU]/333 HU) increase in contrast. No difference was noted in radiation dose or noise between round and oval phantoms (P = .604 and P = .06, respectively), but a small statistically significant difference (1%) in contrast attenuation was demonstrated (P = .025). CONCLUSION: Reduced tube voltage for pediatric contrast material-enhanced CT reduces radiation dose and maintains image contrast. Image noise increases, but the effect is minimal in smaller phantoms. An additional reduction in tube current further reduces radiation dose.

Multi-detector row spiral CT angiography of the thoracic outlet: dose reduction with anatomically adapted online tube current modulation and preset dose savings.

PURPOSE: To evaluate image quality obtained with anatomically adapted online tube current modulation and preset minimum dose savings at multi-detector row spiral computed tomographic (CT) angiography of the thoracic outlet. MATERIALS AND METHODS: A total of 100 patients were evaluated for thoracic outlet arterial syndrome with spiral CT angiography (collimation, 4 x 1 mm; pitch, 1.75) both with and without dose reduction by means of anatomically adapted online tube current modulation and preset minimum dose savings. Preset minimum savings of 20% and of 32% were applied in two groups of 50 patients (groups 1 and 2). In each group, low-dose scanning was performed in 25 patients in the neutral position and in 25 patients after postural maneuver. Tube current-time product, noise, presence and quality of graininess and of linear streak artifacts on transverse CT scans, and diagnostic value of sagittal reformations and volume-rendered images were evaluated and recorded for each data set. chi2 test was used to compare frequencies; paired Wilcoxon rank test, to compare subjective and objective image quality scores. P <.05 indicated a significant difference. RESULTS: In group 1, mean tube current-time product was 3225 mAs for reference scans and 2101 mAs for low-dose scans (mean reduction, 35%; range, 27%-47%). In group 2, mean was 3070 mAs for reference scans and 2068 mAs for low-dose scans (mean reduction, 33%; range, 17%-38%). In group 1, no differences in frequencies of graininess and linear streaking or in noise level were found between images acquired with or without dose reduction. In group 2, no difference was found in noise level between low-dose and reference scans. On low-dose scans, moderate linear streaking was observed with lower frequency and moderate graininess was observed with higher frequency, but artifacts did not compromise image quality or prevent confident assessment of arterial diameter in the three compartments of the thoracic outlet. CONCLUSION: Online tube current modulation with a preset minimum dose saving of 20% allowed 35% reduction in mean tube current-time product, with no loss in image quality.

Ultra-low-dose coronary artery calcium screening using multislice CT with retrospective ECG gating.

The aim of this study was to reduce radiation exposure in multislice CT (MSCT) coronary artery calcium screening using different tube settings, and to determinate its impact on the detection and quantification of coronary artery calcification. Forty-eight patients underwent routine MSCT coronary artery calcium scoring (Somatom VolumeZoom, Siemens, Forchheim, Germany) with retrospective ECG-gated data acquisition. Scanning was performed with a 4 x 2.5-mm collimation. In each patient data acquisition was performed twice using tube settings of 120 kVp with 133 mAs (protocol 1) and of 80 kVp with 300 mAs (protocol 2). Together with the 80-kVp protocol additional online ECG-related tube current modulation (ECG pulsing) was used. Three-millimeter overlapping slices (increment 1.5 mm) were calculated for each data set. Semi-automated calcium quantification was performed calculating absolute Ca-hydroxylapatite mass. In addition to patient examinations, the radiation exposure for both protocols was evaluated using computed tomography dose index (CTDI) phantom measurements. Protocol 2 showed a significantly lower patient radiation exposure than protocol 1 (0.72 vs 2.04 mSv; p<0.0001). The CTDI phantom measurements revealed a 65% reduction of radiation dose. Calcium scoring results of both protocols showed a high correlation ( r=0.99; p<0.0001) for absolute Ca-Hydroxylapatite mass measurements. Using 80-kVp protocols patient radiation exposure can be significantly reduced in MSCT coronary artery calcium screening without affecting the detection and quantification of coronary artery calcification; therefore, this technique should be used with retrospective ECG-gated cardiac CT examinations in patients with regular sinus rhythm.

Advances in cardiac imaging with 16-section CT systems.

RATIONALE AND OBJECTIVES: The authors present advances in electrocardiographically (ECG) gated cardiac spiral scanning with recently introduced 16-section computed tomographic (CT) equipment. MATERIALS AND METHODS: The authors discuss the technical principles of ECG-gated cardiac scanning. They give an overview on system properties and on the detector design. They describe ECG-gated scan- and image-reconstruction techniques and ECG-controlled dose modulation ("ECG pulsing") for a reduction of the patient dose. They discuss key parameters for image quality and present simulation and phantom studies and they give preliminary values for the patient dose. RESULTS: An extension of the adaptive cardiac volume reconstruction for ECG-gated spiral CT provides adequate image quality for up to 16 sections. With the smallest reconstructed section width (about 0.83 mm) and overlapping image reconstruction, cylindrical holes 0.6-0.7 mm in diameter can be resolved in a transverse resolution phantom independent of the heart rate. For coronary CT angiography, the influence of transverse resolution is most pronounced for coronary segments that are only slightly tilted relative to the scan plane. In this case, visualization of stents and plaques is considerably improved with 1.0-mm or smaller section width. For 0.42-second gantry rotation time, temporal resolution reaches its optimum (105 msec) at a heart rate of 81 beats per minute. Effective patient dose for the standard protocols recommended by the manufacturer ranges from 0.45 mSv (male) for ECG-triggered calcium scoring to 7.1 mSv (male) for high-resolution ECG-gated coronary CT angiography. With ECG pulsing, the dose is reduced by 30%-50% depending on the patient's heart rate. CONCLUSION: Clinical experience will be needed to evaluate fully the potential of 16-section technology for cardiac imaging.

Multislice helical CT of the heart with retrospective ECG gating: reduction of radiation exposure by ECG-controlled tube current modulation.

Our objective was to evaluate image quality and radiation exposure of retrospectively ECG-gated multislice helical CT (MSCT) investigations of the heart with ECG-controlled tube current modulation. One hundred patients underwent MSCT scanning (Somatom VolumeZoom, Siemens, Forchheim, Germany) for detection of coronary artery calcifications. A continuous helical data set of the heart was acquired in 50 patients (group 1) using the standard protocol with constant tube current, and in 50 patients (group 2) using an alternative protocol with reduced radiation exposure during the systolic phase. The standard deviations (SD) of predefined regions of interest (ROIs) were determined as a measure of image noise and were tested for significant differences. There was no significant difference between group 1 and group 2 with respect to image noise. Radiation exposure with and without tube current modulation was 1.0 and 1.9 mSv ( p<0.0001), respectively, for males and 1.4 and 2.5 mSv ( p<0.0001), respectively, for females; thus, there was a mean dose reduction of 48% for males and 45% for females, respectively. The ECG-controlled tube current modulation allows significant dose reduction when performing retrospectively ECG-gated MSCT of the heart.