Home Lung Image Quality with 320-row Wide-volume CT Scans The Effect of Prospective ECG-gating and Comparisons with 64-row Helical CT Scans
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Lung Image Quality with 320-row Wide-volume CT Scans The Effect of Prospective ECG-gating and Comparisons with 64-row Helical CT Scans

Posted Mar 31, 2012 Updated Apr 10, 2023
By Tsuneo Yamashiro MD , Tetsuhiro Miyara MD , Masashi Takahashi MD , Ayano Kikuyama MD , Hisashi Kamiya MD , Hisanobu Koyama MD PhD , Yoshiharu Ohno MD PhD , Hiroshi Moriya MD PhD , Mitsuru Matsuki MD PhD , Yuko Tanaka MS , Satoshi Noma MD PhD , Sadayuki Murayama MD PhD
12 min read

Rationales and Objectives

To evaluate the image quality of 320-row wide-volume (WV) computed tomography (CT) scans in comparison with 64-row helical scans for the lung.

Materials and Methods

The Institutional Review Board of each institution approved this prospective, multicenter study and informed consent was obtained. A total of 73 subjects underwent two types of chest CT, including 320-row WV scans and 64-row helical scans. Both scans used the same tube voltage, tube current, exposure time setting, and slice thickness. The helical scans were not electrocardiogram (ECG)-gated. For the WV scans, prospective ECG-gating was used for 38 subjects, whereas the other 35 subjects did not have ECG-gating. Using a 5-point scale from 1 (nondiagnostic) to 5 (excellent), three blinded observers independently evaluated image quality for five lobes and the lingula. The differences in the scores between WV scans and helical scans were compared using Wilcoxon’s signed-rank test.

Results

The WV scans with ECG-gating had significantly higher scores than 64-row helical scans for all lobes and lingula (right lower lobe, P < .01; other lobes and lingula, P < .0001, respectively). The 320-row WV scans without ECG-gating also had significantly higher scores than 64-row helical scans ( P < .05), except for nonsignificant differences for the left upper lobe.

Conclusions

Lung image quality of ECG-gated WV scans, which do not require any additional radiation exposure, is better than that of non–ECG-gated 64-row helical scans. Non–ECG-gated 320-row WV scans are comparable or slightly superior to non–ECG-gated 64-row helical scans.

A 320-row multidetector computed tomography (MDCT) scanner provides a unique scanning method, known as wide-volume (WV) scanning, as well as conventional 64-row helical scanning. The 320-row WV scan is characterized by a long scan field (16-cm length) using a single gantry rotation (step-and-shoot scanning), which makes it possible to obtain volumetric scan data for the entire lung with a few rotations during a single breathhold. In addition, when combined with prospective electrocardiogram (ECG)-gating (triggering), ECG-gated images are obtained without additional radiation exposure.

Although some studies have demonstrated the image quality of 320-row MDCT scans of the heart, brain, and abdominal vessels , published information on 320-row WV scans of the lung is very limited : it remains unclear whether 320-row WV scans have better image quality than 64-row helical scans for depicting the lung field.

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Materials and methods

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Subjects

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CT Scans

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Figure 1, Illustrations of 64-row helical scanning and 320-row wide volume scanning. For 64-row helical scanning (a) , the beam pitch is 0.828 (helical pitch of 53) with a collimation of 0.5 mm × 64, resulting in 12 to 16 gantry rotations for the entire chest. For 320-row wide volume scanning (b) , the detector collimation is 0.5 mm × 320 or ×280 and a series of three rotations covers the entire chest. Note that prospective electrocardiogram (ECG)-gating does not change the total number of gantry rotations, thus requiring the same radiation dose as non–ECG-gated wide-volume scans.

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Qualitative Assessment of Image Quality

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Figure 2, Computed tomography (CT) images of a non-electrocardiogram (ECG)-gated 64-row helical scan (a) and an ECG-gated 320-row wide-volume scan (b) in an 82-year-old male. On a 64-helical CT image (a) , relatively large motion blurs are observed along the margins of the heart ( arrowheads ). The bronchial walls in the left lower lobes are also blurred ( arrows ). Final scores were as follows: four for the right middle lobe; five for the right lower lobe; three for the left lingula; and four for the left lower lobe. On an ECG-gated 320-row wide-volume image (b) , no major motion blur is observed and the bronchial walls in the left lower lobes are clearly visualized. Final scores were five for all lobes and the lingula. Note that these scores for each lobe or the lingula were determined after observing all images including the lobe (lingula), not based on a single image. Also, helical and wide-volume scans for the same subject were randomly presented to the readers from a total of 146 CT scans, which were not shown contiguously or side by side on the screen.

Figure 3, Computed tomography images of a non-electrocardiogram (ECG)-gated 64-row helical scan (a) and a non–ECG-gated 320-row wide-volume scan (b) in a 60-year-old female. Motion blurs caused by the ascending aorta and the pulmonary artery are shown on a non–ECG-gated 64-row helical image ( arrowheads ) (a) . On a non–ECG-gated 320-row wide-volume image, no major motion blur is observed (b) .

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Quantitative Assessment of Image Quality

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Figure 4, An example for measuring standard deviation (SD) of computed tomography density in the thoracic descending aorta. The measured density SD in the circular region of interest is 79.41 HU in this subject.

Figure 5, Examples for measuring cardiac motion blurs in a 32-year-old male. The measured maximum motion blur of the left ventricle was 5.6 mm on the 64-row helical image (a) and 1.4 mm on the 320-row wide-volume image with electrocardiogram-gating (b) .

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Statistical Analysis

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Results

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Interobserver Agreement for Qualitative Assessments

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Table 1

Interobserver Agreement for the Qualitative Assessment

64-row Helical Scans (n = 73) 320-row Wide-volume Scans (n = 73) W_P_ Value W_P_ Value Right upper lobe 0.507 .003 0.564 .0002 Right middle lobe 0.706 <.0001 0.761 <.0001 Right lower lobe 0.609 <.0001 0.659 <.0001 Left upper lobe 0.668 <.0001 0.542 .0006 Left lingula 0.590 <.0001 0.756 <.0001 Left lower lobe 0.730 <.0001 0.811 <.0001 Pulmonary nodule ∗ 0.692 <.0001 0.646 <.0001

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Reproducibility of Quantitative Measurements

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Table 2

Reproducibility of Quantitative Measurements

Mean Difference ± SD Limit of Agreement Intraobserver error SD of attenuation in the descending aorta (HU) −0.63 ± 1.42 −3.47 to 2.20 Maximum motion blur of the left ventricle (mm) 0.11 ± 0.47 −0.83 to 1.04 Interobserver error SD of attenuation in the descending aorta (HU) 0.15 ± 2.95 −5.75 to 6.04 Maximum motion blur of the left ventricle (mm) 0.18 ± 0.51 −0.84 to 1.20

HU, hounsfield unit; SD, standard deviation.

Figure 6, Intra- and interobserver reproducibility for quantitative measurements. Plots show intraobserver (a,b) and interobserver (c,d) errors for attenuation standard deviation of the descending aorta (a,c) and the maximum motion blur of the left ventricle (b,d) , according to the Bland-Altman analysis. The mean of the two measurements and the difference between them are plotted. The mean difference does not appreciably deviate from zero, and the limits of agreement are small.

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Comparisons between Non–ECG-gated 320-row WV Scans and Non-ECG-gated 64-row Helical Scans

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Table 3

Comparisons of Image Quality between Non–ECG-gated Helical Scans and Non–ECG-gated Wide-volume Scans (n = 35)

Mean Scores or Mean ± SD_P_ Value 64-row Helical Scans without ECG Gating 320-row WV Scans without ECG Gating Qualitative assessment ∗ Lung lobe: overall 3.60 3.90 .001 Right upper lobe 4.14 4.40 .04 Right middle lobe 3.60 3.94 .02 Right lower lobe 3.91 4.23 .03 Left upper lobe 4.09 4.20 NS (.50) Left lingula 3.11 3.43 .03 Left lower lobe 2.71 3.17 .03 Pulmonary nodule † 3.56 3.72 NS (.29) Quantitative assessment SD of attenuation in the descending aorta (HU) 94.28 ± 22.65 99.14 ± 23.57 .001 Maximum motion blur of the left ventricle (mm) 5.25 ± 2.08 3.53 ± 1.91 <.0001

WV, wide volume.

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Comparisons between ECG-gated 320-row WV Scans and Non–ECG-gated 64-row Helical Scans

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Table 4

Comparisons of Image Quality between Non–ECG-gated Helical Scans and ECG-gated WV Scans (n = 38)

Mean Scores or Mean ± SD_P_ Value 64-row Helical Scans without ECG Gating 320-row WV Scans with ECG Gating Qualitative assessment ∗ Lung lobe: overall 3.72 4.34 <.0001 Right upper lobe 4.16 4.63 <.0001 Right middle lobe 3.63 4.26 <.0001 Right lower lobe 3.97 4.39 .002 Left upper lobe 4.11 4.63 <.0001 Left lingula 3.45 4.21 <.0001 Left lower lobe 3.03 3.92 <.0001 Pulmonary nodule † 3.83 4.14 .004 Quantitative assessment SD of attenuation in the descending aorta (HU) 93.57 ± 24.57 99.72 ± 25.45 .0002 Maximum motion blur of the left ventricle (mm) 4.42 ± 1.94 2.26 ± 1.26 <.0001

WV, wide volume.

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Comparisons between ECG-gated 320-row WV Scans and Non–ECG-gated 320-row WV Scans

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Table 5

Comparisons of Image Quality between Non–ECG-gated Wide-volume Scans and ECG-gated Wide-volume Scans

Mean Scores or Mean ± SD_P_ Value 320-row WV Scans without ECG Gating (n = 35) 320-row WV Scans with ECG Gating (n = 38) Qualitative assessment ∗ Lung lobe: overall 3.90 4.34 .0001 Right upper lobe 4.40 4.63 .0006 Right middle lobe 3.94 4.26 .0009 Right lower lobe 4.23 4.39 .0004 Left upper lobe 4.20 4.63 .0003 Left lingula 3.43 4.21 <.0001 Left lower lobe 3.17 3.92 <.0001 Pulmonary nodule 3.72 † 4.14 ‡ .02 Quantitative assessment SD of attenuation in the descending aorta (HU) 99.14 ± 23.57 99.72 ± 25.45 NS (.93) Maximum motion blur of the left ventricle (mm) 3.53 ± 1.91 2.26 ± 1.26 .003

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Discussion

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Comparing Prospective ECG-gated WV Scanning with Retrospective ECG-gated Helical Scanning

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Comparing Prospective ECG-gated WV Scanning with Prospective ECG-gated Scanning of Conventional CT Machines

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Positive Effect of Prospective ECG-gating in WV Scanning for Chest CT

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Acknowledgments

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Academic Radiology, Volume 19, Issue 4
Journals General Radiology
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