Exploration the Method of Low Dose Coronary Artery Imaging with Dual-Source CT

doi:10.4236/jbm.2013.11002

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Journal of Biosciences and Medicines, 2013, 1, 6-10 JBM

doi:10.4236/jbm.2013.11002 Published Online February 2013 (http://www.SciRP.org/journal/jbm/)

Published Online February 2013 in SciRes. http://www.scirp.org/journal/jbm

Exploration th e Met h od of Low Dose Coronar y Art ery

Imaging with Dual-Source CT

Zhiwei Huang, Bo Xiao, Lisha Zhong

Department of Bio medi cal Engineering, Lu zhou Medical Co llege, Luzhou, P.R.China

Email: [email protected]

Received 2013

ABSTRACT

Objective: On the pre mise that the image q uality meets

the requirements of clinical diagnosis, we explored

the methods to reduce the radiatio n dose of coronary

artery imaging with Dual-Source CT (DSC T) . Metho d s:

We randomly selected 200 patients with coronary

heat disease (BIM<25kg/m2), applied the scanning

technology of regulating the dose of heart electric

pulse (AUTO) on t he 100 patients in group A . In this

group for different heart rate we chose different full

dose exposure time window. For the 100 patients in

group B, we used conventional full dose (OFF) scan

mode. The DSC T a uto mat ic ally selec ted t he be st t i me

and phase to reconstruct the image. We used the 5

point system to evaluate the image quality, measured

and compared the image noise and radiation dose.

When P<0.05, t he differences between the two groups

have statistical significance. Results: The image

quality scores between the two groups showed no

significant difference (P > 0.05). The average image

noise in gro up A is (41.76 ± 7.98) HU, in group B the

average image noise is (43.97 ± 3.88) HU, the dif-

ference between the two groups was not statistically

significant (P>0.05). The average CTDIvol of group A

and B were (20.63 ± 2.24) mGy, (38.11 ± 10.69) mGy,

respectively, then P <0.01. The average DLP of group

A and B are (235.75 ± 28.64) mGycm and (492.59 ±

125.49) mGycm respectively, then P <0.01, the dif-

ference of radiation dose had statistical significance

(P<0.05). Conclusions: For coronary artery imaging

with DSCT the heart electric pul se (AUTO) regulation

technology can meet the diagnostic requirements and

effectively reduce the radiation dose.

Keywords: Dual-Sou rce CT(DS C T); Corona ry CT

Angiog raphy; L ow dose ; N oi s e;

1. INTRODUCTION

The study sho ws that t he DSCT c oronar y arter y imagin g

has a hi gh d egre e of consistency in the diag nostic results

of coronary stenosis and selective coronary arteriongra-

phy (SCA) [1]. DSCT evaluation on moderate to severe

coronary artery stenosis has higher compliance and con-

sistency with the SC A, DSCT can be used as a noninva-

sive conventional means in clinical screening and diag-

nosis [2]. DSCT has two sets of X-ray tubes and relative

detectors, two sets of DAS systems are installed in 90

degree angle on the rack. Compared with multi-slice

spiral CT ( MSCT), DSCT reaches higher time resol ution,

its detector covers more areas, its scanning speed be-

comes fa ster, so the scan time is gre atly shor ten, and the

radiation doses is significantly reduced by about 15% to

20% [3]. It also has other advantages, such as the pitch

can be automatically adjusted with the heart rate without

the limit of the heart rate, and the negative prognosis is

high [4]. With the appearance of DSCT, the radiation dose

is reduced, but the radiation dose is still widely con-

cerned. The heart disease committee declared that if

2000 patients receive CT examination with the radiation

dose of 10mSv, one of them will suffer from malignant

tumors. For the overall risk of cancer caused by radiation,

male is less than the women, and the gap between men

of different ages, and there is little gap between men of

different ages; but the overall cancer risk of women de-

creases with increasing age [5]. In this paper for coronary

artery imaging with DSCT, we compared heart electric

pulse (AUTO) wit h conventional full-dose (OFF) sc an

mode, compared the image quality, image noise, and

radiation dose of the two sets. Ensurin g the quality of the

image to meet the diagnostic requirements, we tried to

find methods to minimize the radiatio n d ose.

2. MATERIALS AND METHODS

2.1. Case Selection

From May 10, 2012 to May 25, 2012, we randomly se-

lected 200 patients from West China Ho spital of Sichuan

University, these patients were clinical suspected or di-

agnosed with coronary heart disease (BIM<25kg/m2).

100 cases are in group A (63 cases are male, female 37

Z. W. Huang et al. / Journal of Biosciences and Medicines 1 (2013) 6-10

cases are female, their ages were 34 - 82 years old, the

average age was 58 years old ), and in their scanning

mode, we used AUTO scanning mode . Another 100 cas-

es ar e i n gro up B (5 7 cases are male, 43 cases are female,

their ages were 33 - 80 years old, their average age is

56.5 years old), we applied OFF scanning mode on them.

Two groups of patients are not restricted by heart rate,

age and gender, except serious arrhythmia or frequent

premature beats patients. In b oth groups we used retros-

pective cardiac-gated imaging technique.

2.2. Scanning Preparation

We tried to understand whether patients are allergic to

iodine, and their renal functions are normal. We also

tried to eliminate the tension and depression of the pa-

tients. We conducted strict breath training on patients,

and e njoined patie n ts to keep respiratory amplitude con-

sistent for ever y time. The patients are in the supine po-

sition, the feet of the patients entered the CT gantry first.

ECG electrodes were correctly placed, and the leads

with higher R wave were selected. For the patients

without hypotension, we sprayed Nitroglycerin Aerosol

2-3 times under their tongues.

2.3. Scanning Method

2.3.1. Scanning O peratio n

We used the Siemens Somatom Definition as DSCT

scanner. For the patients in group A and B, we applied

the same time resolution, space resolution, rotation

time(0.33s), collimator width (64*0.6mm), image recon-

struction thickness (0.75mm), reconstruction interval

(0.5mm). At the same time, the scanning range (from 1

to 2cm under the bifurcation of trachea to diaphragmatic

surface of heart), contrasted medium injection scheme,

and image processing methods were kept consistent. We

chose Iopamidol (370 mgI/ml) contrast agent and Ger-

many binocular high-pressure syringe (Ulrich Medical),

Syringe needle was placed on the forearm vein. Firstly

physiological saline was injected, then contrast agent

Iopamidol was injected, at last physiological saline was

injected.

2.3.2. Iodine Concentration Monitoring

We used contrast agent tracer method. In the center of

ascending aorta (it is under the tracheal bifurcation and

away from the bi f urc atio n 2-3cm), we chose the region

of interest and detected the CT value, and the threshold

value was set to 100HU. When the CT values in the re-

gion o f i ntere st reac h 100 H U, the CT will automatically

trigge r sca n with a delay of 6s. Pay attention to avoiding

the impact of the superior vena cava.

2.3.3. ECG

We scanned the patients after their heart rate was steady

and used AUTO scanning mode: the exposure range of

the full dose scan mode was a certain time window in

the R-R interval, and the rest exposure dose was 1/4 of

the ful l d ose. The ti me wi ndow o f the ful l do se exp os ure

was in the R-R interval, and this time window corres-

ponded to different heart rate range. For relativel y fast or

slow heart rate, the ful l-dose exposure range in R-R in-

terval was the smallest. For normal heart rate, full-dose

expo sure ran ge was the maximum. O FF scanning mode:

the full dose-exp osure ra nge is the entire R-R interva l .

2.3.4 Ima ge Pos t-processing

We adopted Siemens Syngo Miltimodalit y Workp lace as

the workstation software for automatically selecting the

best time and phase. By calculating the movement speed

of each vessel coronary, the best time and phase were

selected for reconstruction of 0.75mm thickness, so we

got the best corona ry a rtery i mages at systole and dia stole.

We used the software Circulation to perform the image

post-processing, main technologies includes: Maximum

Intensity Projection, Curved Surface Reconstruction),

Volume Reproduction in order to multi-facedly show the

left main of coronar y artery and its main branches Right

Coronary Artery, Anterior Descending and Circumflex

Artery.

2.4. Image Quality Assessment and Radiation

dose Calculation

2.4.1. Image Quality Assessment

Two experienced diagnostic physicians rated images by

using the double-blind method. For the inconsistent

judgments, they jointly and secondly read the film to

reach agreement. We used 5-p oi nt sc al e in t he gr ad i ng of

the image quality. The standard of 5 points is that the

image can be display clearly without artifacts, the blood

flow filling in all the vascular is good. The stand ard o f 4

points is that there is minor artifacts, only a certain sec-

tion o f the mai n cor onar y arte ry is sligh tl y fuzz y without

split-level or ladder-like artifacts, the diagnosis is not

affected. The standard of 3 points is that in the film the

artifacts are medium, more than 1/2 of one coronary ar-

tery trunk is fuzzy, but we can diagnose the illness. The

axial image is rather vague, but the reconstructed image

can be used for diagnosis. The standard of 2 points is

that in the film the artifacts are severe, all the parts of

one coronary artery are fuzzy or discontinuous, parts of

the blood vessels ha ve split-level artifacts, and the diag-

nosis is limited. The standard of 1 point is that the coro-

nary artery can not be recognized, the tube p ulse can no t

be analyzed, and we can not diagnose the illness. If the

score of the image quality can reach 4-5 points, the im-

age can be considered to be a high-quality image; if the

score is 3 points, the image is evaluated image; if the

Z. W. Huang et al. / Journal of Biosciences and Medicines 1 (2013) 6-10

score is 1-2 points, the image has severe artifacts, it can

not be evaluated and is poor image [6].

2.4.2. Radiatio n dose and Image Noise

The dose of X-ray is provided by the equipment. ED is

the effective dose of ra d ia tion in the patient, and it can

be calculated by using the formula ED = DLP × k, where

k=0.017 [7] and DLP is the dose length product. DLP

(myGycm) is displayed on the device. CTDIvol is CT

dose index, it is also displayed on the device. We set

1cm2 region of interest (ROI) which is put on aortic

center, the ROI is on the beginning part of the left and

right coronary arter y and it is also on the level aortic roo t.

We measured the ROI’s CT value, used the value s’ stan-

dard deviation as the image noise. We calculated the

average value of the twice CT values in the left a nd rig ht

coronary artery, and used this average value as the ulti-

mate CT value. Similarly, the average value of the stan-

dard deviation was calculated twice.

2.5. Statistical Method

We analyzed the obtained data by using software

SPSS11.5. We compared the scores’ differences of image

quality between two groups by applying the values of

χ2. We also applied two independent samples t to test

and compare the radiation dose and image noise. If

P<0.05, we thought the difference had statistical signi-

ficance [8].

3. RESULTS

3.1. Image Quality

In Group A, we got 76 cases, for which the score of im-

age quality was 5 point, accounting for 76%. At the same

time we got 4 points in 20 cases, accounting for 20% and

3 points in 4 cases, accounting for 4%, 2 points and 1

point, 0 cases, accounting for 0%. In group B, we got 5

points in 84 cases, accounting for 84% and 4 points in 14

cases, accounting for 14%, 3 points in 2 cases, account-

ing for 2%, 2 points and 1 point 0 cases, accounting for

0% (Shown in Tabl e 1). For all the coronary artery im-

ages whose quality can be evaluated, the difference of

scores between two groups showed no significant dif-

ference (P> 0.05).

Table1. The comparison of the image quality in Group A and

3.2. Image Noise

The average CT value in Group A is (475.1 ± 45.75) HU,

the a vera ge CT va lue i n Group B is (451.1 ± 45.77) HU,

P>0.05. The average image noise in Group A is (41.76 ±

7.9 8) HU, the average i mage noi se in Gro up B is ( 43.97

± 3.88) HU, P> 0.05. The difference of image nose be-

tween Group A and B had no statistical significance, as

sho wn in fol lo wi ng Table 2.

3.3. Radiation Dose

The radiation dose in the process of cardiac coronary

artery examination consists of the following 3 parts:

Scan, Contrast Agent Tracer Scan and Enhanced Scan.

The radiation dose is the sum of these three parts. We

did statistical analysis, and calculated CTDIvol, mean

dose length product (△DLP) and ED, we also compared

the results. In Group A, the average CTDIvol is (20.63 ±

2.24) mGy, in Group B the average CTDvol is (38.11 ±

10.69) mGy, it reduced (17.48 ± 8.45) mGy, and it de-

creased by nearly 1 time, P <0.05. In Group A, the △

DLP is (235.75 ± 28.64)mGycm, in Group B the △DLP

is (492.59 ± 125.49) mGycm, it reduced (256.84 ± 96.85)

mGycm, it decreased more than 1 time, P <0.05. In

Group A the average ED is (4.01 ± 0.49) mSv, in Group

B the average ED is (8.37 ± 2.13) mSv, it reduced (4.36

± 1.64) mSv, it decreased more t h a n 1 t i me , P<0.05. The

radiation dose difference between two groups was statis-

tically significant, as shown in Table 3.

4. DISCUSSIONS

DSCT coronary artery imaging in the diagnosis of car-

diovascular diseases has unique advantages, more and

more clinical cardiologist take CT as an important

Table 2. Comparison of the image noise in Group A and B.

Table 3. Comparison of the radiation dose of the Group A and

Z. W. Huang et al. / Journal of Biosciences and Medicines 1 (2013) 6-10

examination tool for non-invasive coronary artery imag-

ing, it can be used as a supplement Cardiovascular Angi-

ography, sometimes it can even replace Cardiovascular

Angiography. In the process of the entire examination of

DSCT, X-ray dose is large, the radiation hazards it pro-

duces gets more and more attention. In order to follow

the principle of ALARA (as low as reasonable achieva-

ble), many scholars have done a lot of research in this

respect, including hardware, software and optimizing

programs of scan, such as Heart Bowtie, ECG Current

Control, Cardiac noise subtraction filter, etc [9]. But the

factors which affect the image quality are complex, some

of these factors are closely related and influence each

other. Some parameter settings may improve the image

quality, but on the other hand, they may reduce the im-

age quality in another aspect. So we must comprehen-

sivel y co ns i de r, and separately set the parameters of scan

according to the different clinical needs. But it is diffi-

cult for us to balance the various factors to obtain

high-quality images in order to improve the diagnostic

rate. Cur ren tl y, the re i s no sta nda rd for q ualit y co ntr ol i n

cor onar y arter y ima gi ng o f Dua l-So urce CT in o ur co un-

try.

So far, people have paid more and more attention to

the potential hazards of ionizing radiation in CT. When

ionizing radiation is wo rk ing on human body, it can

produce biological impacts and do harm to human body.

The break of the structure of DNA double helix in hu-

man body is the critical damage to the cells. Radiation

induces gene mutations or the break of the double helix

structure, the distortion increases, and eventually, the

radiation can lead to cancer [10]. The reports pointed out

that for every more radiation dose of 10mSv, the mortal-

ity rate will increase by 0.04% [11]. The actual radiation

dose of CT examination is 2-5 times the dose of effec-

tive radiation [12]. The dose of effective radiation mainly

comes from the enhanced period. In the aspect of opti-

mizing scanning program, people mostly focus on con-

trolling the radiation dose of enhanced period. In most

cases, the image quality and the radiation dose have the

inverse relationship. To balance the relationship between

them, we need to change the fixed scan mode. In prac-

tical application, we should pay attention to the individ-

ual conditions of the different patients, such as the size

of the heart, breast size of the female patient s and cardi-

othoracic ratio, etc. According to these conditions, we

determine the appropriate scan mode and scan parame-

ters. So we can achieve the personalized and reasonable

scanning. A recent survey, which is an international re-

search for radiation dose in coronary artery CTA, dis-

plays that the radiation dose in different hospitals have

obvi ous gap , fro m an a vera ge of 5 mSv to an a verage of

30 mSv. This demonstrates that reasonable scan mode

can effectively reduce the radiation dose [13]. Therefore,

on the premise that the ima ge quality meets the require-

ments of clinical diagnosis, it becomes important for us

to effectively reduce the radiation dose in the CTA ex-

amination of coronary artery, and this can reduce the

radiation damage caused by human factors.

Reducing the radiation dose is generally divided into

two categorie s: new low-dose technology and optimizing

scan parameters. The new scanning technology uses the

ECG current modulation technique, Prospective ECG

Trigger Scan Technology and noise red uction al gorithms.

The methods of optimizing scan parameters are lowering

tube current, lowering tube voltage, reducing the scan

rage of Z-axis and reducing the number of scans based

on body mass or body mass index (BMI). In this article,

in order to reduce the radiation dose, we used the tech-

nology of regulating the dose of heart electric pulse

(AUTO), and this technology belongs to retrospective

cardiac-gated i magin g techniq ue. T hrough t he stud y and

analysis, we concluded that the regulation technology of

dose of heart electric pulse (AUTO) can make the image

quality completely meets the requirements of clinical

diagnosis, and compared with the conventional full dose

(OFF), thi s techno logy can significa ntly reduce the radi-

ation dose of (4.36 ± 1.64) mSv, the radiation dose de-

creased more than 1 time. Of course, it also has inade-

quacies: 1. Data acqui sition is not ca rried o ut throughout

the whole cardiac cycle, and we can not analyze the car-

diac function. 2. If the patient’s heart rate in unstable, it

is easy for us to select the wrong full-dose regions. 3. In

the non-full-dose exposure regions of the R-R interval,

the image quality is a little bit worse than that of the

image in full-dose regions. 4. If there are heart prema-

ture beats in the scan, we can not edit the ECG.

The study has t he follo wing limitatio ns. T he ind ividu-

alized scan mode according the patient’s BMI was not

adopted, the radiation dose still has some space to be

reduced, a nd i n thi s a sp ec t t he study s ho uld b e c o nti nue d.

If the post-processing of image only uses one of the two

periods in image reconstruction, we can only reconstruct

the image of one period, therefore the radiation dose will

be reduced by 1 time, and in this aspect can be studied

much fur t her.

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