Effect of Automatic Tube Current Modulation on Radiation Dose and Image Quality for Low Tube Voltage Multidetector Row CT Angiography: Phantom Study

doi:10.1016/j.acra.2009.02.021

Academic Radiology

Volume 16, Issue 8, August 2009, Pages 997-1002

https://doi.org/10.1016/j.acra.2009.02.021 Get rights and content

Rationale and Objectives

To evaluate the effect of automatic tube current modulation on radiation dose and image quality for low tube voltage computed tomography (CT) angiography.

Materials and Methods

An anthropomorphic phantom was scanned with a 64-section CT scanner using following tube voltages: 140 kVp (Protocol A), 120 kVp (Protocol B), 100 kVp (Protocol C), and 80 kVp (Protocol D). To achieve similar noise, combined z-axis and xy-axes automatic tube current modulation was applied. Effective dose (ED) for the four tube voltages was assessed. Three plastic vials filled with different concentrations of iodinated solution were placed on the phantom's abdomen to obtain attenuation measurements. The signal-to-noise ratio (SNR) was calculated and a figure of merit (FOM) for each iodinated solution was computed as SNR²/ED.

Results

The ED was kept similar for the four different tube voltages: (A) 5.4 mSv ± 0.3, (B) 4.1 mSv ± 0.6, (C) 3.9 mSv ± 0.5, and (D) 4.2 mSv ± 0.3 (P > .05). As the tube voltage decreased from 140 to 80 kVp, image noise was maintained (range, 13.8–14.9 HU) (P > .05). SNR increased as the tube voltage decreased, with an overall gain of 119% for the 80-kVp compared to the 140-kVp protocol (P < .05). The FOM results indicated that with a reduction of the tube voltage from 140 to 120, 100, and 80 kVp, at constant SNR, ED was reduced by a factor of 2.1, 3.3, and 5.1, respectively, (P < .001).

Conclusions

As tube voltage decreases, automatic tube current modulation for CT angiography yields either a significant increase in image quality at constant radiation dose or a significant decrease in radiation dose at a constant image quality.

Section snippets

Anthropomorphic Phantom

An adult-sized, whole-body female anthropomorphic phantom (Model 702; CIRS Inc, Norfolk, VA) was used to assess specific organ doses. The phantom was composed of 38 2.5-cm-thick sectional slabs fabricated of epoxy resin to simulate accurately the physical density and x-ray interaction of various human tissues. Phantom specifications were height, 160 cm; weight, 55 kg; abdominal dimension (anteroposterior × lateral), 17 × 22 cm; and pelvic dimension, 19 × 31 cm. To simulate contrast-enhanced

Effective Dose

The highest ED was measured for the 140-kVp protocol (5.38 mSv ± 0.33) and the lowest for the 100-kVp protocol (3.89 mSv ± 0.46) (Table 1). There was no statistically significant difference for the ED among the four different protocols (P = .12).

Image Quality Assessment

The mean attenuation values of the three iodinated solutions increased as the tube voltage dropped from 140 to 80 kVp. Comparing the mean attenuation values at 140 kVp with those at 120, 100, and 80 kVp, the percentage increases in mean attenuation were

Discussion

Our anthropomorphic phantom demonstrated that an automatic tube current modulation technique for CT angiography steadily increases the SNR of the simulated iliac arteries at a constant radiation dose while the tube voltage was reduced from 140 to 80 kVp. The twofold gain in SNR at 80 kVp compared to 140 kVp was caused by two factors. First, the attenuation values of iodinated contrast material increased at lower tube voltages, where mean photon energies approximate the k edge of iodine (33.2

References (20)

C. Briguori et al.
Contrast agent–associated nephrotoxicity
Progress in cardiovascular diseases
(2003)
C. Schueller-Weidekamm et al.
CT angiography of pulmonary arteries to detect pulmonary embolism: improvement of vascular enhancement with low kilovoltage settings
Radiology
(2006)
A. Waaijer et al.
Circle of Willis at CT angiography: dose reduction and image quality—reducing tube voltage and increasing tube current settings
Radiology
(2007)
C.M. Heyer et al.
Image quality and radiation exposure at pulmonary CT angiography with 100- or 120-kVp protocol: prospective randomized study
Radiology
(2007)
B. Wintersperger et al.
Aorto-iliac multidetector-row CT angiography with low kV settings: improved vessel enhancement and simultaneous reduction of radiation dose
Eur Radiol
(2005)
Y. Nakayama et al.
Lower tube voltage reduces contrast material and radiation doses on 16-MDCT aortography
AJR Am J Roentgenol
(2006)
D.V. Sahani et al.
16-MDCT angiography in living kidney donors at various tube potentials: impact on image quality and radiation dose
AJR Am J Roentgenol
(2007)
C. Herzog et al.
Pediatric cardiovascular CT angiography: radiation dose reduction using automatic anatomic tube current modulation
AJR Am J Roentgenol
(2008)
Z. Szucs-Farkas et al.
Effect of X-ray tube parameters, iodine concentration, and patient size on image quality in pulmonary computed tomography angiography: a chest-phantom-study
Investigative radiology
(2008)
S. Rizzo et al.
Comparison of angular and combined automatic tube current modulation techniques with constant tube current CT of the abdomen and pelvis
AJR Am J Roentgenol
(2006)

There are more references available in the full text version of this article.

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For ROI1 at the level of the carotid bifurcation, VMIs showed a higher CNR than the 120 kV SE group (p = 0.028)/ 90 kV SE group (p = 0.037) when their energy level were lower than 79 keV (56.92 ± 16.01)/56 keV (90.08 ± 22.14) respectively. The 90 kV SE (80.68 ± 24.47) showed the best CNR in all the SE groups. For CNRD, the 120/90/80 kV SE group was equivalent to 83/63/67 keV VMIs respectively. For ROI2 at the level of the origin of the common carotid artery, VMIs also showed a higher CNR than the 120 kV SE group (p = 0.015)/90 kV SE group (p = 0.034) when their energy level were lower than 83 keV (46.31 ± 14.47)/60 keV (72.23 ± 16.96) respectively. The 90 kV SE (64.98 ± 18.51) showed the best CNR in all the SE groups. For CNRD, the 120/90/80 kV SE group was equivalent to 88/72/75 keV VMIs respectively. The highest subjective rating score was 50 keV TBDE(3.70 ± 0.53). Cohen's Kappa values(0.79–0.85) suggest a substantial level of agreement between the two observers.
The novel TBDE technique with low keV VMI reconstruction provides better image quality of carotid CTA than the low tube voltage scan in the SE mode. VMIs with a keV level below 56 keV have a higher CNR than those from SE scans with 80/90/120 kV. Subjectively, the optimal keV energy level in TBDE for carotid CT angiography is 50 keV.
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Original investigationEffect of Automatic Tube Current Modulation on Radiation Dose and Image Quality for Low Tube Voltage Multidetector Row CT Angiography: Phantom Study

Rationale and Objectives

Materials and Methods

Results

Conclusions

Section snippets

Anthropomorphic Phantom

Effective Dose

Image Quality Assessment

Discussion

Progress in cardiovascular diseases

CT angiography of pulmonary arteries to detect pulmonary embolism: improvement of vascular enhancement with low kilovoltage settings

Radiology

Circle of Willis at CT angiography: dose reduction and image quality—reducing tube voltage and increasing tube current settings

Radiology

Image quality and radiation exposure at pulmonary CT angiography with 100- or 120-kVp protocol: prospective randomized study

Radiology

Aorto-iliac multidetector-row CT angiography with low kV settings: improved vessel enhancement and simultaneous reduction of radiation dose

Eur Radiol

Lower tube voltage reduces contrast material and radiation doses on 16-MDCT aortography

AJR Am J Roentgenol

16-MDCT angiography in living kidney donors at various tube potentials: impact on image quality and radiation dose

AJR Am J Roentgenol

Pediatric cardiovascular CT angiography: radiation dose reduction using automatic anatomic tube current modulation

AJR Am J Roentgenol

Effect of X-ray tube parameters, iodine concentration, and patient size on image quality in pulmonary computed tomography angiography: a chest-phantom-study

Investigative radiology

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

AJR Am J Roentgenol

Original investigation
Effect of Automatic Tube Current Modulation on Radiation Dose and Image Quality for Low Tube Voltage Multidetector Row CT Angiography: Phantom Study