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KMID : 1149020180200020071
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Journal of Korean Society of Computed Tomographic Technology
2018 Volume.20 No. 2 p.71 ~ p.78
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A study on the dose reduction effect of low-voltage 70 kVp protocol test and the usefulness of image in the CT Scanning Thyroid
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Lee Byung-Hyun
Lee Sang-Hun
Myung Seung-Gil
Kim Do-Hoon
Kang Dong-Won
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Abstract
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Purpose: In order to investigate the dose reduction effect and the usefulness of the 70 kVp protocol by comparing the image quality between the high-voltage 120 kVp protocol, currently used in the clinical CT test of Cervical(Thyroid with Neck) which is implemented to confirm thyroid nodule and lymph node metastasis After ultrasound examination and the low-voltage 70 kVp using CARE kV.
Material and methods: In 64 patients who underwent cervical(neck) CT after thyroid nodule was found by ultrasound examination, the control group (32 patients) applied the tube voltage 120 kVp protocol, whereas the experimental group(32 patients) applied the tube voltage 70 kVp protocol. Regarding the quantitative evaluation of the images, signal to noise ratio (SNR), contrast to noise ratio (CNR) and CT HU (Hounsfield Unit) were measured and compared by setting the common carotid artery (CCA), the internal jugular vein (IJ vein), the Sternocleidomastoid muscle (SC muscle), and the region of interest (ROI) and noise. Statistical analysis was implemented by independent sample t-test using PASW (PASW statistics, ver. 18.0, SPSS, Chicago, USA). Regarding the qualitative evaluation, the survey was conducted with criteria of highly agree (5point), agree (4points), average (3point), disagree(2points), strongly disagree(1point) after the blind test for one cervical(neck) CT reading specialist and eight residents. The dose assessment was implemented by comparing and analyzing DLP values shown in the Dose report after the test.
Result: As a result of quantitative evaluation, HU value has significant difference between control group (A) and experimental group (B) in Common carotid artery, internal jugular vein and Sternocleidomastoid muscle (CCA: (A) 188.22±22.33 vs (B) 248.57±33.99, I.J vein: (A) 186.51±22.98 vs (B) 244.55±33.89, S.C muscle: (A) 73.52±6.78 vs (B) 69.39±5.89 p<0.05). Image noise was significantly higher in the experimental group (B) than in the control group (CCA: (A) 4.41±1.09 vs (B) 5.75±0.97, I.J vein: (A) 4.23±1.25 vs (B) 5.97±0.99, S.C muscle (A) 3.42±0.97 vs (B) 5.53±1.34 Background: (A) 1.64±0.48 vs (B) 2.54±0.46 p<0.05). SNR was not significantly different between the control group (A) and the experimental group (B)in common carotid artery and internal jugular vein, but had a significant difference in the sternocleidomastoid muscle. (CCA: (A) 45.02±11.73 vs (B) 44.41±9.66, p=0.821, I.J vein: (A) 47.61±14.251 vs (B) 44.03±47.61, p=0.233, S.C muscle (A) 21.95±5.79 vs (B) 16.84±2.59 p<0.05). CNR has no significant between control (A) and experimental group (B) (CCA: (A) 75.65±25.87 vs (B) 72.86±19.74, p=0.629, I.J vein: (A) 74.46±25.78 vs (B) 71.14±18.80, p=0.558). As a result of the qualitative evaluation, recognition of the image quality of the experimental group and the control group was very low (2.45±4.31). In the experimental group, the recognition of insufficiency about the image quality (1.915±2.691) and the recognition of the readability (1.212±1.178) were also very low. The dose assessment showed a significant difference in the DLP values between the control group (A) and the experimental group.(DLP(A) 393.50±51.96 vs DLP(B) 98.69±30.58 p<0.05).
Conclusion: The image quality and the patient dose reduction effect were evaluated by comparing and analyzing the 120kVp protocol which was previously used upon CT test of Cervical(Thyroid with Neck) and the protocol which sets its tube voltage to 70kVp by using CARE kV. Compared to the conventional the high tube voltage protocol of 120kVp, the low tube voltage protocol of 70 kVp was able to obtain a suitable image for diagnosis of a thyroid nodule and lymph node metastasis with using a small amount of contrast medium and was able to reduce patient dose effectively. Therefore, the low tube voltage protocol is expected to be very useful for the patient with thyroid disease.
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KEYWORD
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Thyroid, CARE kV, Low tube voltage, Patient Dose
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