Automatic Tube Current Modulation Technique Research Articles

Automatic tube current modulation for volume scan in a 320-detector row CT scanner

The x-y plane combined with z-axis automatic tube current modulation (ATCM) technique is one of the most comprehensive approaches to CT dose reduction because the radiation dose is adjusted according to patient attenuation in three dimensions. The 320-detector row CT scanner has the widest scan range (16 cm) within one axial rotation and equips with volume scan ATCM (VS-ATCM) mode. Special attention is needed while utilizing VS-ATCM mode in CT acquisitions especially scanning different anatomical regions, such as neck and shoulder in a single volume. However, the mechanism of VS-ATCM of the 320-detector row CT scanner remains unclear. This study aims to evaluate the performance of VS-ATCM mode in a 320-detector row CT scanner. A phantom set consists of three simple-shaped phantoms was scanned with the VS-ATCM mode. A solid-state detector was inserted into the central position of the phantom set to measure the real-time dose profiles at seven positions within five scan volumes. The effective tube-current time product of each slice was recorded. The standard deviation of the CT numbers measured at each image slice was used as a noise measurement. The performance of helical scan ATCM (HS-ATCM) mode was in comparison of VS-ATCM mode. The results indicated that VS-ATCM mode can provide a less dose CT scanning to a patient but resulted in a higher image noise in comparison with those of HS-ATCM mode. In clinical practice, radiologists or radiological technologists should pay more attention on the volume position when using VS-ATCM mode for patient imaging. Our experience can be a reference to others for implementation of clinical practices.

The application of automatic tube current modulation (ATCM) on image quality and radiation dose at abdominal computed tomography (CT): A phantom study

Multi-phase spiral Computed tomography (CT) of abdomen has been widely used as an effective imaging modality to diagnose variety of diseases. As a result, the accumulated radiation exposure on the abdomen is substantially higher than other human organ regions. According to ALARA (as low as reasonably achievable) principle, how to control radiation dose without compromising imaging quality becomes a research topic of high interest. However, how to achieve dose optimization of the abdomen CT examinations in Chinese patients have not been fully investigated in previous studies. In this study, we develop an abdomen-equivalent tissue model made by well-known CTP579 auxiliary testing model and the real CT data acquired from 68 Chinese male subjects. Combining with catphan600, we simulated the visibility of low and high contrast objects at adult abdomen under variety of x-ray dose levels. Using the automatic tube current modulation (ATCM) technique, we reduced the total radiation dose and identified a proper noise index (NI) for Chinese patients to maintain low or high contrast detectability of abdominal CT image. Our numerical experiments showed that in the phantom study for Chinese patients, when a NI was set at 10, the radiation dose reduced by 34.3% with low contrast objects detectable, while setting NI at 14 the dose level decreased by 65.1% without change the detectability of high contrast targets. The subjective ratings from three radiologists also yielded high consistence with Kappa > 0.75. This study demonstrated the feasibility of performing the CT dose optimization studies through a unique phantom with the ATCM method.

Adenosine-stress dynamic myocardial perfusion imaging using 128-slice dual-source CT: optimization of the CT protocol to reduce the radiation dose

The aim of this study was to compare the radiation dose and image quality of different adenosine-stress dynamic myocardial perfusion CT protocols using a 128-slice dual-source computed tomography (DSCT) scanner. We included 330 consecutive patients with suspected coronary artery disease. Protocols employed the following dynamic scan parameters: protocol I, a 30-s scan with a fixed tube current (FTC, n = 172); protocol II, a 30-s scan using an automatic tube current modulation (ATCM) technique (n = 108); protocol III, a 14-s scan using an ATCM (n = 50). To determine the scan interval for protocol III, we analyzed time-attenuation curves of 26 patients with myocardial perfusion who had been scanned using protocol I or II. The maximum attenuation difference between normal and abnormal myocardium occurred at 18.0 s to 30.3 s after initiation of contrast injection. Myocardial perfusion images of FTC and ATCM were of diagnostic image quality based on visual analysis. The mean radiation dose associated with protocols I, II, and III was 12.1 ± 1.6 mSv, 7.7 ± 2.5 mSv, and 3.8 ± 1.3 mSv, respectively (p < 0.01). Use of a dose-modulation technique and a 14-s scan duration for adenosine-stress CT enables significant dose reduction while maintaining diagnostic image quality.

Comparison of image quality and radiation dose between combined automatic tube current modulation and fixed tube current technique in CT of abdomen and pelvis

Tube current is an important determinant of radiation dose and image quality in X-ray-based examination. The combined automatic tube current modulation technique (ATCM) enables automatic adjustment of the tube current in various planes (x-y and z) based on the size and attenuation of the body area scanned. To compare image quality and radiation dose of the ATCM with those of a fixed tube current technique (FTC) in CT of the abdomen and pelvis performed with a 16-slice multidetector row CT. We reviewed 100 patients in whom initial and follow-up CT of the abdomen and pelvis were performed with FTC and ATCM. All acquisition parameters were identical in both techniques except for tube current. We recorded objective image noise in liver parenchyma, subjective image noise and diagnostic acceptability by using a five-point scale, radiation dose, and body mass index (BMI, kg/m(2)). Data were analyzed with parametric and non-parametric statistical tests. There was no significant difference in image noise and diagnostic acceptability between two techniques. All subjects had acceptable subjective image noise in both techniques. The significant reduction in radiation dose (45.25% reduction) was noted with combined ATCM (P < 0.001). There was a significant linear statistical correlation between BMI and dose reduction (r = -0.78, P < 0.05). The ATCM for CT of the abdomen and pelvis substantially reduced radiation dose while maintaining diagnostic image quality. Patients with lower BMI showed more reduction in radiation dose.

Organ dose evaluation for multi-slice spiral CT scans based on China Sichuan chest anthropomorphic phantom measurements

The authors measured organ radiation doses during multi-slice computed tomography (MSCT) chest scans using a China Sichuan anthropomorphic phantom (CDP-1C). Chest CT images from live volunteers based on automatic tube current modulation (ATCM) techniques were similar to those obtained using the CDP-1C phantom, indicating that the phantom accurately modelled the anatomic structure and X-ray absorbance of the human torso. Indeed, attenuation values differed by <5%. Organ radiation doses were measured using thermoluminescence dosemeters in the CDP-1C. With increased noise index, the CT dose index, the dose-length product and the average organ dose all decreased. Thus, the CDP-1C phantom can also assess dose levels during CT examinations in Chinese patients. The noise index (based on ATCM techniques) should be set to 8.5 or higher to reduce X-ray exposure while maintaining appropriate resolution for diagnosis.

The measurement of organic radiation dose of multi-slice CT scanning by using the Chinese anthropomorphic chest phantom

Objective Using the Chinese anthropomorphic chest phantom to measure the absorbed dose of various tissues and organs under different noise index, and to assess the radiation dose of MSCT chest scanning with the effective dose(ED). Methods The equivalence of the Chinese anthropomorphic chest phantom(CDP-1C) and the adult chest on CT sectional anatomy and X-ray attenuation was demonstrated. The absorbed doses of various tissues and organs under different noise index were measured by laying thermoluminescent dosimeters(TLD) inside the phantom, and the corresponding dose-length products(DLP) were recorded. Both of them were later converted into ED and comparison was conducted to analyze the dose levels of chest CT scanning with automatic tube current modulation (ATCM) under different noise index. Student t-test was applied using SPSS 12.0 statistical software. Results The Phantom was similar to the human body on CT sectional anatomy. The average CT value of phantom are -788.04 HU in lung,45.64 HU in heart,65.84 HU in liver,254.32 HU in spine and the deviations are 0.10%,3.04%, 4.49% and 4.36% respectively compared to humans. The difference of average CT value of liver was statistically significant(t=-8.705,P＜0.05),while the differences of average CT values of lung, heart and spine were not significant(t value were -0.752,-1.219,-1.138,respectively and P＞0.05).As the noise index increased from 8.5 to 22.5, the DLP decreased from 393.57 mGy·cm to 78.75 mGy·cm and the organs dose declined. For example, the average absorbed dose decreased from 22.38 mGy to 3.66 mGy in lung. Compared to ED calculating by absorbed dose, the ED calculating by DLP was lower. The ED values of the two methods were 6.69 mSv and 8.77 mSv when the noise index was set at 8.5. Conclusions Application of the Chinese anthropomorphic chest phantom to carry out CT dose assessment is more accurate. The noise index should be set more than 8.5 during the chest CT scanning based on ATCM technique. Key words: Phantoms, imaging; Densitometry,X-ray; Radiation dosage

CT Dose Index and Patient Dose: They AreNotthe Same Thing

Estimates of individual patient risk, and epidemiologic studies assessing potential late effects, must use patient size–specific dose estimates—they cannot use only scanner output (volume CT dose index or dose-length product).

Patient Size Compensated Automatic Tube Current Modulation in Multi-detector Row CT of the Abdomen and Pelvis

To evaluate the performance of a patient size-compensated automatic tube current modulation (PSC-AutomA) technique from the perspectives of image quality and radiation dose in multi-detector-row computed tomography (MDCT) scan of the abdomen and pelvis. Institutional review board approval was obtained and the study was Health Insurance Portability and Accountability Act-compliant. One hundred and seventeen patients (mean age: 48.8 years; range: 17-89 years; male/female: 57/60) underwent abdominal-pelvic CT scan on a 64-slice MDCT using the noise indexes (NI) recommended by the PSC-AutomA technique. Two radiologists independently evaluated all examinations for noise, streak artifacts, and diagnostic acceptability at the dome of liver, porta hepatis, and the upper margin of acetabulum. The CT dose index (CTDI) volume and effective dose of the CT performed using a recommended NI were compared to the CT performed using a fixed NI of 12. Statistical analysis of the data was performed with nonparametric tests. The NI recommended by the PSC-AutomA technique was strongly correlated with patient size (r = 0.98, P < .001) with a mean NI of 14.2 HU. The recommended NI of 98.2% (115/117) patients was different from the fixed NI of 12. Approximately 71.8% (84/117) subjects were scanned with a NI higher than 12, whereas 26.5% (31/117) subjects were scanned with a NI lower than 12. All examinations (100%; 117/117) were graded as possessing diagnostic image quality. Compared with the CT performed by using a fixed NI 12, the overall CTDI and effective dose reduction by the PSC-AutomA technique were 11.1% and 11.8%, respectively. The PSC-AutomA technique can recommend an appropriate NI in MDCT scan of the abdomen and pelvis according to patient size, allowing a balanced optimization of both radiation dose and image quality, simultaneously.

Does the amount of tagged stool and fluid significantly affect the radiation exposure in low-dose CT colonography performed with an automatic exposure control?

To determine whether the amount of tagged stool and fluid significantly affects the radiation exposure in low-dose screening CT colonography performed with an automatic tube-current modulation technique. The study included 311 patients. The tagging agent was barium (n = 271) or iodine (n = 40). Correlation was measured between mean volume CT dose index (CTDI (vol)) and the estimated x-ray attenuation of the tagged stool and fluid (ATT). Multiple linear regression analyses were performed to determine the effect of ATT on CTDI (vol ) and the effect of ATT on image noise while adjusting for other variables including abdominal circumference. CTDI (vol) varied from 0.88 to 2.54 mGy. There was no significant correlation between CTDI (vol) and ATT (p = 0.61). ATT did not significantly affect CTDI (vol) (p = 0.93), while abdominal circumference was the only factor significantly affecting CTDI (vol) (p < 0.001). Image noise ranged from 59.5 to 64.1 HU. The p value for the regression model explaining the noise was 0.38. The amount of stool and fluid tagging does not significantly affect radiation exposure.

Detection of urolithiasis using low-dose CT—A noise simulation study

How does an acquisition at reduced doses using automatic tube current modulation techniques compare to the normal standard dose CT? Does it affect the sensitivity for detection of calcifications? CT raw data of 54 patients with suspected urolithiasis acquired with automatic tube current modulation techniques were used for image noise simulations with 100%, 50% and 25% dose simulated. Data were analyzed by independent readers with regard to the presence of urolithiasis, stone location, size, density and differential diagnoses. The mean effective dose per standard examination/50%/25% simulation was 7.3 mSv/3.8 mSv/1.9 mSv. Sensitivities/specificities for detection of urolithiasis were calculated for all dose simulations and resulted in 0.94/0.98 in the 50% dose level group and 0.82/0.97 in the 25% dose level group. Low-dose CT with tube current modulation can be used as a standard procedure for the evaluation of patients with suspected acute renal colic.

Use of automatic tube current modulation with a standardized noise index in young children undergoing chest computed tomography scans with 64-slice multidetector computed tomography

The automatic tube current modulation (ATCM) technique is available on multidetector computed tomography (MDCT) scanners, and its dose reduction benefits in clinical applications have been documented primarily in adult patients. To evaluate the use of ATCM to reduce radiation dose while maintaining consistent image quality for young children undergoing 64-slice MDCT chest scans. Chest scans (120 kV, small-scan field of view, 5-mm image slice thickness) were performed for 50 consecutive young children (0.2-3 years) using 64-slice volume computed tomography (VCT) with ATCM method and a noise index (NI) of either 8 or 9, depending on the patient's age. The scanner automatically selected the actual tube current based on NI values and patient attenuation as determined by scout scans for the study group. Image quality and volume-weighted CT dose index (CTDI(vol)) values (measured with small-scan field of view and 16-cm diameter CTDI phantom) were compared with images from a control group of 50 children acquired earlier using a standard protocol with fixed tube current. Two experienced pediatric radiologists assessed image quality, including resolution, noise, and artifacts, on a five-point scale. Scores greater than or equal to 3 were considered to be clinically acceptable. The mean image quality score and CTDI(vol) for the study and control groups were 3.46 and 2.34+/-0.71 mGy, and 4.65 and 6.68+/-0.62 mGy, respectively. While there was a statistically significant decrease in image quality in the study group, all studies had acceptable image quality, and CTDI(vol) with ATCM was about 65% lower than that with fixed tube current. The average image noise for the control group was 4.78+/-0.58, versus 7.53+/-0.42 and 8.28+/-0.40 for children under and above 1 year of age, respectively, in the study group. Despite a higher average noise level, the study group with ATCM demonstrated a lower standard deviation of image noise. The z-axis ATCM method produces consistent image quality for young children undergoing 64-slice MDCT chest scans. With noise levels of NI=8 and 9 at 5-mm image slice thickness, one may obtain clinically acceptable images with significantly reduced radiation dose.

Image Noise and Radiation Dose Using an Automatic Tube Current Modulation Technique at 64-Detector Computed Tomography

We describe the effect of the off-center position, the bowtie filter type, and the direction of scan projection radiograph on the radiation dose and image noise of 64-detector computed tomographic scans using the automatic tube current modulation technique. On anteroposterior scan projection radiographs, the tube current ratio increased, with an increase in the off-center position of the phantom irrespective of the filter size. On lateral scan projection radiographs, it remained constant with each bowtie filter type regardless of the off-center phantom position.

Comparison of Image Quality and Radiation Dose between Fixed Tube Current and Combined Automatic Tube Current Modulation in Craniocervical CT Angiography

The combined automatic tube current modulation (ATCM) technique adapts and modulates the x-ray tube current in the x-y-z axis according to the patient's individual anatomy. We compared image quality and radiation dose of the combined ATCM technique with those of a fixed tube current (FTC) technique in craniocervical CT angiography performed with a 64-section multidetector row CT (MDCT) system. A retrospective review of craniocervical CT angiograms (CTAs) by using combined ATCM (n = 25) and FTC techniques (n = 25) was performed. Other CTA parameters, such as kilovolt (peak), matrix size, FOV, section thickness, pitch, contrast agent, and contrast injection techniques, were held constant. We recorded objective image noise in the muscles at 2 anatomic levels: radiation exposure doses (CT dose index volume and dose-length product); and subjective image quality parameters, such as vascular delineation of various arterial vessels, visibility of small arterial detail, image artifacts, and certainty of diagnosis. The Mann-Whitney U test was used for statistical analysis. No significant difference was detected in subjective image quality parameters between the FTC and combined ATCM techniques. Most subjects in both study groups (49/50, 98%) had acceptable subjective artifacts. The objective image noise values at shoulder level did not show a significant difference, but the noise value at the upper neck was higher with the combined ATCM (P < .05) technique. Significant reduction in radiation dose (18% reduction) was noted with the combined ATCM technique (P < .05). The combined ATCM technique for craniocervical CTA performed at 64-section MDCT substantially reduced radiation exposure dose but maintained diagnostic image quality.

Quantitative assessment of image noise and streak artifact on CT image: Comparison of z-axis automatic tube current modulation technique with fixed tube current technique

The purpose of our study is to quantitatively assess the effects of z-axis automatic tube current modulation technique on image noise and streak artifact, by comparing with fixed tube current technique. Standard deviation of CT-values was employed as a physical index for evaluating image noise, and streak artifact was quantitatively evaluated using our devised Gumbel evaluation method. z-Axis automatic tube current modulation technique will improve image noise and streak artifact, compared with fixed tube current technique, and will make it possible to significantly reduce radiation doses at lung levels while maintaining the same image quality as fixed tube current technique.

Misoperation of CT Automatic Tube Current Modulation Systems with Inappropriate Patient Centering: Phantom Studies

Inappropriate patient centering on the gantry changes the size of the localizer radiographs used for CT examinations, influencing the operation of CT automatic tube current modulation because tube current is controlled with information from localizer radiographs. The purpose of this study was to examine the influence of inappropriate patient centering on the gantry isocenter on automatic tube current modulation. An elliptical phantom was scanned with four automatic tube current modulation techniques after acquisition of localizer radiographs in the horizontal and vertical directions with the phantom center shifted from the gantry isocenter in the vertical direction. After scanning, the magnification rate of the frontal localizer radiographs, tube current-time product, and image noise were examined. On phantom studies, the magnification rate of localizer radiographs showed a linear relation to the vertical deviation of the phantom from the gantry isocenter. From 50 mm above to 50 mm below the gantry isocenter, tube current-time products ranged from 75% to 141% compared with those at the gantry isocenter. In addition, increases and decreases in the amount of image noise related to changes in tube current-time product were confirmed. Inappropriate patient centering causes misoperation of automatic tube current modulation systems, in which tube current is controlled with information from localizer radiographs, and thus causes increases in tube current or image noise.

Chest CT Performed with 3D and z-Axis Automatic Tube Current Modulation Technique : Breast and Effective Doses

Chest computed tomographic (CT) scans are the most effective examinations for detecting lung cancer at an early stage. In chest CT examinations, it is important to consider the reduction of radiation dose, particularly to the mammary gland. The objective of this study was to assess breast doses and effective doses on chest CT examinations between three-dimensional and z-axis automatic tube current modulation (ATCM) techniques. Absorbed dose to the breast, lung, mediastinum, and skin was evaluated with an anthropomorphic phantom and radiophotoluminescence glass dosimeters using two different CT scanners. The dosimeters were placed inside and outside the phantom. The phantom was scanned using three-dimensional and z-axis ATCM techniques after scanning localizer radiographs from the horizontal and vertical directions. After scanning, each organ dose was calculated. Moreover, the dose-length product recorded in the dose reports was examined, and each effective dose was calculated. Compared with z-axis ATCM, three-dimensional ATCM reduced breast dose by 0.7% to 18.6% and effective dose by 4.9% to 10.2%. In particular, three-dimensional ATCM reduced frontal breast dose. For other organs, three-dimensional ATCM reduced absorbed doses by 3.4% to 13.6% compared to z-axis ATCM. Three-dimensional ATCM can reduce absorbed doses to the breast and other organs, in addition to reducing effective dose, compared to z-axis ATCM.

Thyroid Shields versus z-Axis Automatic Tube Current Modulation for Dose Reduction at Neck CT

To assess the effectiveness of in-plane bismuth thyroid shields and a z-axis automatic tube current modulation (ATCM) technique with respect to dose reduction and image noise in the thyroid and other regional tissues during neck computed tomography (CT). Because this was a phantom study, neither institutional review board approval nor HIPAA compliance was required. A female phantom, thyroid shields, and an eight-section CT scanner were used. Radiation dose was measured by using thermoluminescent dosimetry (TLD) chips placed in the phantom's thyroid, cervical bone marrow, and soft tissues. Scans were performed by using fixed tube current and a z-axis ATCM technique with and without shields. Image noise was quantified as the standard deviation of the attenuation value (in Hounsfield units) on CT images. Thyroid dose was 76.9 mGy with an unshielded fixed tube current technique. Use of shields and ATCM reduced this dose to 44.7 mGy (42% reduction, P < .001) and 17.0 mGy (78% reduction, P < .001), respectively. The combination of shields and ATCM further reduced this dose to between 11.9 and 12.9 mGy (83%-85% reduction, P < .001), depending on the shield's presence in the scout scan. ATCM resulted in minimized tube current throughout the neck, which reduced dose-length product across the entire scan volume by 60% (926 vs 368 mGy . cm). Thyroid bed noise was lowest (3.9 HU) during the fixed tube current technique without shields, with noise slightly higher (6.9 HU) with the unshielded ATCM technique (P < .001). Thyroid image noise was markedly higher when using shields (P < .001), with noise measuring between 74 and 113 HU for fixed tube current and ATCM scans. z-Axis ATCM is more effective than shields at reducing thyroid radiation dose during neck CT. Shields combined with ATCM slightly further reduces dose; however, this is associated with higher image noise.

WE‐E‐332‐03: Evaluating Effective Doses and Image Quality for Multislice CT Using Automatic Tube Current Modulation

Purpose: Automatic tube current modulation (ATCM) is one of innovative techniques to lower radiation doses in computed tomography (CT) scanning. The purpose of this study is to estimate the image quality, organ doses and effective doses in clinical multi‐detector CT examinations using ATCM techniques. Method and materials: An anthropomorphic phantom was scanned on a Siemens Sensation 64 multi‐detector CT scanner with CARE Dose4D software which offered nine combinations of ATCM. The scanning regions included head, neck, chest, abdomen and pelvis. The image quality was derived from noise distributions in each image slice using MatLab. Organ does and effective doses were measured by high sensitivity thermoluminescent dosimeters (LiF: Mg, Cu, P) which were inserted into the anthropomorphic phantom at the selected organs. Results: CARE Dose 4D software tends to trigger increasing intensity modulation in the parts of shoulder (upper lung) and lower lung, but to trigger decreasing intensity modulation in the parts of head, neck, middle lung, abdomen and pelvis. Effective doses from ATCM were lower than those from fix tube current except neck examinations. The dose decreases vary from 36% to 68.5% in head examinations, 12.0% to 38.9% in chest examinations, 31.4% to 43.4% in abdomen examinations, and 33% to 55.5% in pelvis examination, but the dose increases are from 18.4% to 48% in neck examinations. The noise increase ratios, which were derived from the images using ATCM comparing with those using fix tube current, are from −1.9% to 2.5%, −15.0% to −19.9%, −13.1% to 0.7%, 7.6% to 15.7%, and 16.2% to 28.0% in head, neck, chest, abdomen and pelvis examinations, respectively. Conclusion: ATCM techniques with appropriate use could reduce effective doses but slightly increase image noises. ATCM is an efficient method to reduce patients' radiation doses during CT scanning if there is no influence on the diagnostic acceptability.

SU‐GG‐I‐44: Real‐Time Dose Measurements of Automatic Tube Current Modulation in Multislice CT

Purpose: To estimate real‐time doses which are controlled by automatic tube current modulation (ATCM) in multidetector computed tomography (MDCT), and to verify the dose decrease with the prediction by software. Method and Materials: Brilliance 40 MDCT scanner (Philips) provides five ATCM methods. Those are automatic current selection (ACS), xy‐plane dose modulation (D‐DOM), z‐axial dose modulation (Z‐DOM), ACS combined D‐DOM, and ACS combined Z‐DOM. Real‐time doses were measured by two CT pencil‐type detectors operating with a Barracuda (RTI‐e) electrometer connected to a PC running the software oRTIgo2002 (RTI‐e). One detector is DCT10 CTDI ion chamber (RTI‐e) with 100 mm sensitive length. The other is CT‐SD16 CT slice detector (RTI‐e) with 160 mm sensitive length. Several geometric phantoms, which are circular, oval, and elliptic cylinders with 15 cm height, were fabricated to simulate body shapes and to verify the xy‐plane dose modulation. An Apollo phantom was also fabricated to verify the z‐axial dose modulation. Results: For circular cylindrical phantoms with 16–24 cm diameter, doses decreased 28–69% for ACS, 28–67% for ACS combined D‐DOM, and 24–66% for ACS combined Z‐DOM. But dose increased 13–20% for 32 cm diameter. For oval and elliptic cylindrical phantoms, doses decreased 17–27% for ACS, 15–40% for D‐DOM, 31–39% for ACS combined D‐DOM, and 15–28% for ACS combined Z‐DOM. D‐DOM and Z‐DOM real‐time dose variation curves were similar for circular cylindrical phantoms. However, real‐time dose variation curves got closed along with increasing diameter. For oval and elliptic cylindrical phantoms, ACS and ACS combined Z‐DOM real‐time dose variations were resembling. But Z‐DOM real‐time dose variations were remarkable for the Apollo phantom. Conclusion: The methods established by this study could investigate the real‐time dose variations. Using ATCM techniques in MDCT scanning could decrease patient doses. However, it needs to pay more attention to use ATCM techniques for obese patients.

Automatic tube current modulation technique for multidetector CT: is it effective with a 64-detector CT?

To investigate whether it is possible to obtain adequate images at uniform image noise levels and reduced radiation exposure with our automatic tube current modulation (ATCM) technique for 64-detector CT. The study population consisted of 64 patients with known or suspected lung or abdominal disease. We used a 64-detector CT scanner (LightSpeed VCT, GE Healthcare, Waukesha, WI, USA) and a combined angular and longitudinal tube current modulation technique (Smart mA, GE Healthcare, Waukesha, WI, USA) to examine 34 patients. The scanning parameters were identical; the minimum and maximum tube current thresholds were 50 and 800 mA, respectively. For study of the constant tube current technique, 30 additional patients were examined at 350 mA. The CT number and image noise (SD of the CT number) were measured in the 64 patients at six levels, i.e., the center of the left ventricle, the liver dome, the porta hepatis, the center of the spleen and the right and left renal pelvis. When we used the ATCM technique, the mean image noise ranged from 8.40 at the center of the left ventricle to 11.31 at the porta hepatis; the mean tube current ranged from 105.9 mAs at the center of the left ventricle to 169.6 mAs at the center of the spleen. The mean dose reduction rate per constant tube current at 175 mAs ranged from 3.1 to 39.5%. By use of the ATCM technique, it is possible to maintain a constant image noise level with a 64-detector CT.