Balancing Radiation and Contrast Media Dose in Single-Pass Abdominal Multidetector CT

Rationale and Objectives

As both contrast and radiation dose affect the quality of CT images, a constant image quality in abdominal contrast-enhanced multidetector computed tomography (CE-MDCT) could be obtained balancing radiation and contrast media dose according to the age of the patients.

Materials and Methods

Seventy-two (38 Men; 34 women; aged 20–83 years) patients underwent a single-pass abdominal CE-MDCT. Patients were divided into three different age groups: A (20–44 years); B (45–65 years); and C (>65 years). For each group, a different noise index (NI) and contrast media dose (370 mgI/mL) was selected as follows: A (NI, 15; 2.5 mL/kg), B (NI, 12.5; 2 mL/kg), and C (NI, 10; 1.5 mL/kg). Radiation exposure was reported as dose–length product (DLP) in mGy × cm. For quantitative analysis, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were calculated for both the liver (L) and the abdominal aorta (A). Statistical analysis was performed with a one-way analysis of variance. Standard imaging criteria were used for qualitative analysis.

Results

Although peak hepatic enhancement was 152 ± 16, 128 ± 12, and 101 ± 14 Hounsfield units ( P < .001) for groups A, B, and C, respectively, no significant differences were observed in the corresponding SNR L with 9.2 ± 1.4, 9.1 ± 1.2, and 9.2 ± 3. Radiation (mGy × cm) and contrast media dose (mL) administered were 476 ± 147 and 155 ± 27 for group A, 926 ± 291 and 130 ± 16 for group B, and 1981 ± 451 and 106 ± 15 for group C, respectively ( P < .001). None of the studies was graded as poor or inadequate by both readers, and the prevalence-adjusted bias-adjusted kappa ranged between 0.48 and 0.93 for all but one criteria.

Conclusions

A constant image quality in CE-MDCT can be obtained balancing radiation and contrast media dose administered to patients of different age.

As radiation exposure resulting from multidetector computed tomography (MDCT) technology has become a major issue in the radiologic community, radiologists should accept the primary responsibility of minimizing the radiation dose delivered to patients while preserving the image quality and diagnostic efficacy of the CT examination . As the lifetime risk of radiation-induced cancer is greater the younger is the patient at the time of exposure, this radiation consciousness should be greatest with patients aged <30 years .

Several technical and electronic dose reduction strategies have been developed and successfully applied in clinical practice such as the automatic tube current modulation and the use of iterative reconstruction algorithms in place of the filtered back projection . Moreover, with the advent of dual-source CT, the effect of low-kilovoltage protocols on radiation dose and image quality has also been investigated . In particular, it has been shown that a significant reduction of the radiation dose with an acceptable image quality can be obtained by coupling the reduction of the peak kilovoltage with the use of adaptive iterative reconstruction algorithms .

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Materials and methods

Population

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CT Technique

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Tdelay=CI+25−TSD T

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Image Analysis

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Quantitative Analysis

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SNRL=μL/meanSDL;SNRA=μA/meanSDA. S

;

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CNRL=(μL−μF)/σ;CNRA=(μA−μF)/σ C

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FOML=CNR2L/ED F

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Qualitative Analysis

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Statistical Analysis

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Results

Patient Characteristics

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Table 1

Patient Characteristics

Characteristic Group A ( n = 27) Group B ( n = 28) Group C ( n = 17)P Value Age (years) 20–44 (35 ± 9) 45–65 (56 ± 8) >65 (74 ± 7) — Gender M ( n = 14); F ( n = 13) M ( n = 14); F ( n = 14) M ( n = 10); F ( n = 7) — Weight (kg) 62 ± 12 65 ± 9 71 ± 10 NS Height (cm) 167 ± 9 165 ± 7 167 ± 8 NS BMI (kg/m 2 ) 21.6 ± 3 24 ± 2 26 ± 4 NS GFR (mL/min) 106 ± 25 98 ± 40 41 ± 13 <.01 Creatinine (mg/mL) 0.84 ± 0.16 0.80 ± 0.23 1.65 ± 0.42 <.01

BMI, body mass index; F, female; GFR, glomerular filtration rate; M, male; NS, not significant.

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Nonionic Iodinated Contrast Media

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Table 2

Dose–Length Products (DLP), Effective Doses (ED), Volumes of Contrast Media (CM) Injected, Iodine Loads, and Scan Delays of the CT Acquisition Performed in Each Group

Parameter Group A Group B Group C_P_ Value DLP (mGy *cm) 476 ± 147 926 ± 291 1981 ± 451 <.001 ED (mSv) 7.1 ± 2.2 13.9 ± 4.3 29.7 ± 6.7 <.001 CM (cc) 155 ± 27 130 ± 16 106 ± 15 <.001 Iodine load (g) 58 ± 11 49 ± 6 39 ± 5 <.001 Scan delay (s) 77 ± 7 78 ± 6 82 ± 8 NS

NS, not significant.

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Effective Absorbed Dose

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Scan Delays

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Quantitative Image Analysis

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Table 3

Mean Attenuation Values (HU), Contrast-to-Noise Ratios (CNR), and Signal-to-Noise Ratios (SNR) for Liver ( L ) and Abdominal Aorta ( A ) Are Shown Along with the Figure of Merit for CNR L and the Image Noise (σ) for Each Group

Parameter Group A Group B Group C_P_ Value Mean liver (HU) 152 ± 16 128 ± 12 101 ± 14 <.01 CNR L 16.7 ± 2 18.8 ± 3 21.7 ± 4.4 <.01 SNR L 9.2 ± 1.4 9.1 ± 1.2 9.2 ± 3 NS FOM 41.8 ± 17 30 ± 17 16 ± 6 <.001 Mean aorta (HU) 221 ± 23 224 ± 51 205 ± 35 NS CNR A 21 ± 2.4 26.6 ± 5.5 32 ± 6 <.01 SNR A 12 ± 2.4 14.5 ± 3.3 17.4 ± 5.5 <.01 Sigma (σ) 15 ± 0.6 12 ± 0.5 10 ± 1.7 <.01

HU, Hounsfield unit; NS, not significant.

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Qualitative Image Analysis

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Table 4

Qualitative Analysis: Prevalence-Adjusted Bias-Adjusted Kappa (PABAK) and Grade of Interobserver Agreement for Each Image Quality Criteria Are Shown

Sharp Reproduction PABAK Agreement Intrahepatic portal veins 0.81 Almost perfect Hepatic veins 0.81 Almost perfect CBD 0.29 Fair CBD in the pancreas 0.48 Moderate Gallbladder walls 0.93 Almost perfect Splenic artery 0.5 Moderate Portal vein and SMV 0.75 Substantial Aorta and IVC 0.87 Almost perfect Coeliac trunk 0.87 Almost perfect SMA 0.81 Almost perfect

CBD, common biliary duct; IVC, inferior vena cava; SMA, superior mesenteric artery; SMV, superior mesenteric vein.

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Discussion

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Acknowledgment

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References

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Balancing Radiation and Contrast Media Dose in Single-Pass Abdominal Multidetector CT

Rationale and Objectives

Materials and Methods

Results

Conclusions

Materials and methods

Population

CT Technique

Image Analysis

Quantitative Analysis

Qualitative Analysis

Statistical Analysis

Results

Patient Characteristics

Nonionic Iodinated Contrast Media

Effective Absorbed Dose

Scan Delays

Quantitative Image Analysis

Qualitative Image Analysis

Discussion

Acknowledgment

References

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