Comparison of Image Quality and Dose between Intra-Venous and Intra-Arterial Liver Dynamic CT using MDCT

MDCT를 이용한 역동적 간 컴퓨터단층촬영 검사에서 정맥과 동맥 주입법에 따른 영상의 화질 및 선량 비교

Abstract

The purpose of this study was to analyze differences in imaging quality and dose difference between intra-venous (IV) and intra-arterial (IA) liver dynamic computed tomography (CT). Herein, retrospective, blinded analysis was conducted to analyze signal-to-noise and contrast-to-noise ratios in cases of patients who underwent IV or IA liver dynamic CT for transarterial chemoembolization (TACE), an interventional procedure for hepatocellular carcinoma. The dose length product (DLP) value stored in Picture Archive and Communication System (PACS) was used to calculate the effective dose and thereby compare differences in the dose between the two methods. The mean liver and spleen signal to noise ratio (SNR) was greater in IV-liver dynamic CT than in IA-liver dynamic CT; however, contrast to noise ratio (CNR) was higher in IA-liver dynamic CT than in IV-liver dynamic CT. However, there were no differences in DLP and effective dose between the two methods. In conclusion, our findings showed that IA-liver dynamic CT showed a similar effective dose and superior CNR compared with IV-liver dynamic CT. Further studies must analyze 3D angiography CT of the hepatic artery to clearly distinguish the feeding artery, which is the essential step in interventional procedures for hepatocellular carcinoma.

본 연구에서는 정맥경유 역동적 간 조영 컴퓨터단층촬영 검사와 동맥경유 역동적 간 조영 컴퓨터단층촬영 검사의 영상의 질과 선량의 차이를 분석하고자 하였다. 간세포암종의 중재적 시술인 경도관동맥화학색전술 대상으로 정맥과 동맥 경유 역동적 간 조영 컴퓨터단층촬영 검사를 한 케이스를 후향적 블라인드 방법으로 신호대잡음비와 대조도대잡음비를 분석하였다. 또한 영상저장 및 전송체계에 저장된 Dose Length Product (DLP)값을 이용하여 유효선량을 구하여 두 검사의 선량 차이를 분석하였다. 신호대잡음비는 정맥경유 역동적 간 조영 컴퓨터단층촬영 검사가 간과 지라에서 높은 결과를 보였지만 대조도대잡음비는 동맥경유 역동적 간 조영 컴퓨터단층촬영 검사가 높았다. 하지만 DLP와 유효선량 비교에서는 두 검사 간 차이가 발생하지 않았다. 결론적으로 동맥경유 역동적 간 조영 컴퓨터단층촬영 검사가 정맥경유 역동적 간 조영 컴퓨터단층촬영 검사에 비해 선량차이가 발생하지 않으면서도 대조도대잡음비가 우수한 검사임을 확인하였다. 추가로 간세포암종의 중재적 시술에서 가장 중요한 부분이 섭식동맥의 구분이 명료한가에 대한 구분이 필요하기 때문에 간동맥의 삼차원 혈관조영 컴퓨터단층촬영 검사에 대한 분석이 필요하다고 사료된다.

Ⅰ. INTRODUCTION

Computed tomography (CT) can be largely divided into two types by the X-ray beam shape: cone beam CT (CBCT) and fan beam CT (FBCT). CBCT has superior spatial resolution compared with FBFT; however, CBCT shows limitations in the diagnosis of soft tissue lesions^[1]. In studies comparing CBCT and FBCT images, FBCT provided better soft tissue differentiation and anatomical visualization compared with CBCT, suggesting it is more suitable for human body CT^[2]. Among the representative methods of FBCT, multi detector CT (MDCT) enables prompt imaging of a wide area, and hence, it offers many benefits in dynamic imaging of arterial, portal venous, and venous phases^[3]. In particular, clear differentiation of the feeding artery is essential in liver dynamic CT using MDCT for hepato-cellular carcinoma (HCC) diagnosis. As HCC receives over 90% of its nutrients from the hepatic artery, accurate identification of the feeding artery of HCC is important. In particular, transcatheter arterial chemoembolization (TACE) is conducted to embolize the feeding artery of HCC, and identifying all the feeding arteries of HCC is a key determinant of successful procedure. In liver dynamic CT, the contrast medium is generally injected intra-venously. A contrast agent is injected intra-venously and travels through the heart and aorta to be imaged along with several arteries in the abdomen. TACE involves puncturing the femoral artery and placing the catheter tip in the proper hepatic artery to conduct liver dynamic CT^[4]. As many interventional fluoroscopes in Korea are offered as CBCT type, many previous studies compared images acquired with IA-liver dynamic CT and IV-liver dynamic CT. However, currently, there is a lack of studies that analyzed images acquired using the two methods in MDCT. Therefore, herein, this study aimed to retrospectively analyze differences in imaging quality, and dose of IV-liver dynamic CT and IA-liver dynamic CT conducted using MDCT.

Ⅱ. MATERIALS AND METHODS

Patients who visit our institution are generally diagnosed with HCC using IV-liver dynamic CT, and those with adequate indications receive TACE. To conduct TACE, the right femoral artery was punctured, and a 4-French diagnostic catheter was placed in the proper hepatic artery. Subsequently, IA-liver dynamic CT was conducted in the CT scan room (Fig. 1).

Fig 1. Diagnosis of HCC with IV-liver dynamic CT using retrospectively collected data(A), catheter insertion for IA-liver dynamic CT (B), IA-liver dynamic CT(C), Post TACE image (D)

PACS data collected from 50 patients who completed the described procedures were analyzed. Patient information was blinded, and this study was exempted from review by the Institutional Review Board (IRB). IV-liver dynamic CT was conducted using MDCT (IQon Spectral CT, PHILPS, Netherlands) with Automatic Exposure Control (AEC) function and Imax300 (300 mgl/mL, IMAS DIAGNOSTIC IMAGING, CO Cork, Ireland) containing 30% iodine was used as the contrast medium. An 18-G needle was used to secure the medium injection path. IA-liver dynamic CT was conducted using MDCT (IQon Spectral CT, PHILPS, Netherlands) with AEC function, and 4-French Introducer Set and 0.035-inch Guide Wire (150 cm, Terumo, Japan, Tokyo) were injected, and a 4-French Yashrio Catheter (Yashiro, JUNGUNG MEDICAL, Korea) was used. IV-liver dynamic CT conditions were as follows: tube voltage 120 kVp, tube current 92 mAs, slice thickness 3 mm, rotation time 0.33, pitch 0.609 mm/rot, matrix 512×512, and algorithm Sharp (c). IA-liver dynamic CT conditions were as follows: tube voltage 120 kVp, tube current 82 mAs, slice thickness 3 mm, rotation time 0.33, pitch 0.609 mm/rot, matrix 512×512, and algorithm Sharp (c). Typically, IV-liver dynamic CT images are acquired as follows. An 18G needle was used to secure a vein in the arm, which was connected to an automated contrast medium injector. The contrast medium was injected at a rate of 4 ml per second for a total volume in ml equivalent to twice the body weight. Arterial phase images were acquired 15 seconds after the non-ionic contrast medium was injected. IA-liver dynamic CT images were acquired during TACE, and a standard IA-liver dynamic CT procedure is as follows. An 18G needle was used to puncture the right femoral artery, and a 0.035-inch Guide Wire was injected to conduct TACE. To protect the right femoral artery, a 4-French sheath was injected, and a 4-French diagnostic catheter was used to select the proper hepatic artery. The procedure site was covered with a sterilized cloth to prevent contamination, and the patients were transferred to the CT scan room. To prevent contamination of the sterile area, the 4-French diagnostic catheter was connected to an automated contrast medium injector. The contrast medium was injected at a rate of 1.5 ml per second for a total volume of 30 ml. Arterial phase images were acquired as the contrast medium was injected. IA-liver dynamic CT was used to identify the feeding artery of HCC, and TACE was initiated (Fig. 2).

Fig 2. Insertion of the 4-French sheath after right femoral artery puncture (A), 4-French diagnostic catheter (arrow) placed in the proper hepatic artery (B), examination in CT scan room (C), HCC feeding artery embolization in intervention room (D)

For both IV- and IA-Liver dynamic CT, region of interest (ROI) was set for the liver (segment 5), spleen, and background to measure Hounsfield (HU) value for each. A total of 50 patients in each of the IV- and IA-liver dynamic CT groups were retrospectively analyzed. As a result, a total of 300 sets of data with 150 sets for each IV- and IA-liver dynamic CT were obtained (Fig. 3). The data were used to calculate SNR as shown in Eq. (1)^[5].

Fig 3. Setting ROI in IV-liver dynamic CT (A), evaluating the mean value of set ROI (B), Avg indicates the mean value (C), IV-liver dynamic CT in the upper panel and IA-liver dynamic CT in the lower panel for the same method (D)

\(\begin{aligned}S N R=\frac{R O I_{\text {mean }}}{R O I_{S D}}\end{aligned}\)       (1)

SNR was obtained by dividing the mean ROI by the ROI standard deviation (SD). CNR was calculated using Eq. (2)^[5].

\(\begin{aligned}C N R=\frac{\text { Background }_{\text {mean }}-R O I_{\text {mean }}}{\text { Background }_{S D}}\end{aligned}\)       (2)

CNR is a value showing the level of contrast in ROI by background noise and was observed by calculating the difference between the average value of the background and ROI, which was then divided by Background standard deviation. Lastly, the dose length product (DLP) of all data was extracted using the INFINITE PACS (Version 3.0.11.6 BN1) program. As shown in Eq. (3), Eq. (4), and Eq. (5), DLP was converted to effective dose^[6].

\(\begin{aligned}C T D I_{v o l}=\frac{C T D I_{w}}{\text { pitch }}\end{aligned}\)       (3)

DLP = CTDI_vol × Scanlength       (4)

ED = DLP × CF

ED = Effective Dose, CF = Conversion Factor       (5)

DLP and effective dose were compared with reference to the abdomen, and the effective dose was calculated by multiplying DLP by the abdominal factor (0.015)^[7,8]. SPSS (Version 20.0, IBM, USA) program was used to test the normality of 50 male and female patients. An Independent sample T-test was conducted to compare the measured SNR, CNR, DLP, and the average effective dose. A p-value < 0.05 was considered statistically significant.

Ⅲ. RESULT

Table 1 shows the results of SNR, CNR, DLP, and effective dose of the liver and spleen calculated by IV-liver dynamic CT and IA-liver dynamic CT using MDCT. The mean liver SNR was 4.1 ± 1.1 in IV-liver dynamic CT, which was significantly higher than 3.5 ± 1.3 in IA-liver dynamic CT (p < 0.05). The mean spleen SNR was 6.0 ± 1.8 in IV-liver dynamic CT, which was significantly higher than 3.5 ± 3.5 in IA-liver dynamic CT (p < 0.05). The average liver and spleen CNR was -4.5 ± 3.1, in IV-liver dynamic CT, which was significantly lower than the average CNR, 8.9 ± 5.8 in IA-liver dynamic CT (p < 0.05). There were no differences in DLP and effective dose between IV-liver dynamic CT and IA-liver dynamic CT (p > 0.05).

Table 1. Comparison of Liver dynamic CT with IV and IA

※. IV-LDCT=Intra-venous Liver Dynamic CT,

※. IA-LDCT=Intra-arterial Liver Dynamic CT

SNR=Signal to Noise Ratio, CNR=Contrast to Noise Ratio

LDP=Dose Length Product, ED=Effective Dose

Ⅳ. DISCUSSION

The liver, unlike other organs, receives a dual blood supply: 75% of the blood flow from the portal vein and the rest 25% from the hepatic artery. However, liver cancer gradually leads to decreased blood supply from the portal vein to the liver tissue, and as a result, the liver receives blood mostly from the hepatic artery. In such cases, liver dynamic CT using MDCT can identify lesions to diagnose liver cancer, and IA-liver dynamic CT is used to differentiate the feeding artery and thereby conduct TACE. Herein, we aimed to compare the imaging quality and dose between IA-liver dynamic CT and liver dynamic CT using MDCT.

Patients who underwent TACE were followed-up for nine months to retrospectively analyze data of 50 patients who underwent IA-liver dynamic CT during liver dynamic CT and TACE. Arterial phase axial images were acquired from the two tests to extract the HU value of background, liver, and spleen and hence calculated SNR, CNR, DLP, and effective dose. DLP and effective dose were not significantly different between IV-liver dynamic CT and IA-liver dynamic CT. In contrast, CNR was greater in IA-liver dynamic CT than in IV-liver dynamic CT.

Although our findings showed that IA-liver dynamic CT provides images with better CNR compared with IV-liver dynamic CT, IA-liver dynamic CT is not a mandatory test during TACE. Rather, it is a special examination conducted to the needs of the operator. IA-liver dynamic CT has the benefits of angiography and CT; however, inhomogeneous injection of the contrast medium may lead to difficulties in interpreting the images, which may lead to false-positive findings. In a study by Jung et al.^[9], IA-liver dynamic CT may have technical problems in obtaining homogeneous contrast enhancement of the liver parenchyma due to arterial portosystemic shunt or anatomic modification of the hepatic artery. Such inhomogeneous contrast enhancement of the liver parenchyma may lead to difficulties in interpreting the images. Additionally, IA-liver dynamic CT has complex procedures requiring the patients to travel between the CT scan room and the angiography room, is invasive, and its cost-effectiveness is questioned in that the examination cost is high. In contrast, IV-liver dynamic CT has high specificity and sensitivity and is often used to diagnose liver cancer in clinical practice^[10]. This method is also minimally invasive, only involving intra-venous needle injection using the arm, which has low risks of infection and hence, can be conducted for other general tests. The liver can also be examined via ultrasound; however, this relies on the subjective evaluation of the examiner^[11]. On the other hand, IV-liver dynamic CT using MDCT injects a contrast medium to clearly distinguish liver segments for objective examination. Therefore, both IV- and IA-liver dynamic CT provides high-quality images for the diagnosis of lesions. However, both methods may cause blooming artifacts when an undiluted contrast medium is used^[12], and this can subsequently lead to difficulties in identifying the feeding artery. Therefore, further studies must investigate the optimal dilution ratio of contrast medium to remove blooming artifacts observed with undiluted contrast medium.

A limitation of the study was that as this was a retrospective study, independent variables were already observed, making it impossible to control the variables that had occurred during the study. However, despite this limitation, our study is significant as our findings showed that IA-liver dynamic CT has no difference in the effective dose and higher CNR compared with IV-liver dynamic CT. Further studies must compare 3D CT angiography images of the two methods for accurate image analysis of the hepatic artery. Our findings provide basic data for such additional studies.

Ⅴ. CONCLUSION

In conclusion, IA-liver dynamic CT using MDCT showed a similar effective dose and higher CNR compared with IV-liver dynamic CT. However, as IA-liver dynamic CT is a test to identify the feeding artery of liver cancer in HCC patients rather than a test to investigate the signal amplitude of the liver parenchyma, there are limitations in the interpretation of this study's findings. Therefore, an additional study is required to analyze the 3D Angiography images of the Hepatic Artery, and it is expected that this study will provide basic data.