Article, Radiology

Optimal CT protocol for the diagnosis of active bleeding in abdominal trauma patients

a b s t r a c t

Objectives: The aim of this study is to compare the radiologic diagnostic performance of arterial pHase, portal phase and combined phase computed tomography (CT) for traumatic Abdominal injury. In addition, this study is attempted to decrease lifetime attributable risks (LARs) of cancer due to radiation exposure.by using optimal CT protocol.

Materials and methods: A total of 114 consecutive patients with a traumatic abdominal injury and an abdominal hematoma on CT were enrolled at a single tertiary regional trauma center between January 2016 and March 2017. Each CT protocol set was independently reviewed by three radiologists, and the diagnostic performance of all three CT phases were compared with regard to the capability to detect active bleeding, contained vascular injuries, and organ injuries. Additionally, LARs for cancer incidence and mortality were calculated using dose- length product values, for each phase of CT.

Results: The pooled area under the receiver operating characteristic curves for the diagnosis of active bleeding, contained vascular injuries, and organ injuries ranged from 0.910 to 0.922, 0.643 to 0.723, and 0.948 to 0.915 for arterial, portal, and combined phase CT, respectively. There was no statistically significant difference in the di- agnosis of active bleeding and organ injuries for any combination of two phase sets. The mean LARs for cancer incidence was 0.059%, 0.062% and 0.121% during arterial, portal and combined phase CT, respectively.

Conclusion: Single phase CT could be a potential protocol for abdominal trauma patients. Use of single phase CT could significantly decrease the incidence of radiation-associated cancer in the future.

(C) 2018

Introduction

Currently, abdominal pelvic computed tomography (CT) is most commonly used as the imaging modality to evaluate patients with abdominal trauma [1]. CT provides a rapid and accurate diagnosis of active bleeding and organ damage in trauma patients [2-7]. The detec- tion of active bleeding and vascular injuries is crucial in identifying the need for optimal intervention (surgery or Transcatheter embolization) [1,8-11].

The classic pattern of active bleeding is focal extravasation of con- trast media in the initial CT phase, and enlarged and faded contrast media within the hematoma in delayed images [12]. In the emergency department, physicians usually perform multiphase CT scans due to concern over misdiagnosis of active bleeding or organ injuries in patients with trauma. However, there are no regulated CT protocols

* Corresponding author.

E-mail address: [email protected] (S.J. Choi).

1 Se Jong Kim and Su Joa Ahn contributed equally to this work.

for patients with abdominal trauma [1,8]. Hence, effective radiation doses of conventional multiphase abdominal pelvic CT scans exceed 10-mSv or even 30-mSv at some institutions [13,15]. Cohort studies have shown that radiation exposure from CT is associated with carcino- genesis, especially in children and young adults. The use of the biphasic CT scans before the age of 40 years caused one additional cancer in an estimated 1000 patients as compared with using single phase CT scan. Because traumatic injury is the leading cause of death in young adults, it is important to reduce the radiation dose in patients with trauma [17]. It is important to balance the risk of radiation exposure with the benefits of making a clinically accurate diagnosis. An incomplete or sub- optimal study may lead to repeat or additional tests, ultimately adding to the total radiation dose. Thus, every effort should be made to decrease the radiation dose delivered using a revised protocol or low-radiation setting without compromising the diagnostic capability of the CT study [18-20]. The aim of this study is to compare the radiologic diag- nostic performance between single phase (arterial or portal venous pHase) and combined (both) phase CT for traumatic abdominal injury. In addition, this study is attempted to decrease lifetime attributable

https://doi.org/10.1016/j.ajem.2018.10.011

0735-6757/(C) 2018

risks (LARs) of cancer due to radiation exposure by using optimal CT protocol.

Material and methods

Patient population

Our retrospective study was approved by institutional review board, which waived the requirement for informed consent. The trauma regis- try and the picture archiving and communication system were queried to identify 201 consecutive patients (age >= 16 years) who sustained ab- dominal injury from blunt or penetrating trauma between January 2016

and March 2017, and were seen at our regional trauma center. Patients were excluded if: 1) there was no visible hematoma within the abdominoPelvic cavity on CT (n = 78), 2) the CT protocol did not in- clude both arterial and portal venous phase (n = 6), 3) the CT imaging was delayed beyond 48 h of admission (n = 3). Finally, 114 patients were included in the study.

CT protocol

In our hospital, a 64 detector CT scanner (Somatom Definition Edge; Siemens Medical Solutions, Forchheim, Germany) has been used exclusively for emergency patients. The images of the arterial and portal venous phases were obtained using a bolus tracking method, with delays of 18 and 50 s, respectively, after 100 Hounsfield units enhance- ment of the descending aorta were reached. We included seven patients who underwent outside two phase abdomino-pelvis CT scans.

CT image interpretation

Two board-certified abdominal radiologists (S.J.A and S.J.C, with 4 and 7 years of experience, respectively), and one board-certified general radiologist (D.H.P with 4 years of experience) reviewed all the images; they had no access to other images or clinical information. The radiolo- gists interpreted three different sequences of image sets, each time in a random order: (1) first interpreting Arterial phase only, (2) second interpreting portal venous phase only and (3) finally interpreting both phases. Each interpretation was separated by N6 weeks to reduce recall bias. During each interpretation session, the three radiologists assessed the images to diagnose whether there was active bleeding or contained Vascular injury.

Reference standards

Abdominal hematoma was defined as high attenuation (45-70 HU) fluid adjacent to and directly abutting the injured organ on CT scans. Active bleeding on CT scans was defined as extravasation of contrast enhanced blood from injured organs [8]. Contained vascular injury, including pseudoaneurysm or arteriovenous fistulas, was defined as foci of contained extravasation of contrast enhanced blood within the injured organ [8]. Active bleeding was finally confirmed by surgery or angiography within 24 h after admission. If the patient died without any further interventions or imaging, the final diagnosis was decided effective dose estimates”>by reviewers’ consensus.

CT effective dose estimates

Age- and sex-specific effective doses were analyzed for each body region. Effective dose was used for the quantitative risk assessment of radiation exposure. Effective dose of each CT examination was calculated using dose-length product (DLP, mGy * cm) values, and the normalized values of conversion factors (EDLP) found in the International Commission on Radiological Protection (ICRP) publica-

tion 103 [21].

The formula used for calculating the effective dose was as follows:

Effective dose(mSv) = DLP x EDLP

The Cumulative effective dose value in two-phase CT was

calculated by summing the effective doses for each CT scan (arterial and portal venous).

Estimation of LARs of radiation-induced Cancer

The DLP values of both single CT phases, conversion constant (EDLP) from ICRP publication 103, and age- and sex-specific factors based on Biological Effects of Ionizing Radiation VII methodology, were used to estimate the LARs for radiation-induced cancer inci- dence and mortality [21,22]. Biological Effects of Ionizing Radiation VII data points were interpolated to the nearest integer age of exposure by using linear interpolation [23]. The DLP value of the two phases CT was calculated as the sum of each single phase DLP value. The probability of reducing cancer incidence and mortality could be predicted by comparing the LAR values obtained in the two- phase and single-phase CT, respectively.

Statistical analysis

The diagnostic performance, in terms of detecting active bleeding, was measured in terms of area under the receiver operating characteristic (ROC) curve (AUC), as well as sensitivity and specificity. McNemar’s test was used to compare for differences in diagnostic performance with different modality sets. Mean values of continuous variables with normal distributions were compared using Student’s t-test. We used statistical

Table 1

Patient demographics.

Characteristics Study sample, n (%)

Age (years)–mean +- SD

Male 40.5 +- 18.9

Female 56.3 +- 22.3

Sex ratio (M/F) 82 (72%)/32 (28%)

Injury mechanism, n (%)

Traffic collision 79 (79/114, 70%)

Fall 19 (19/114, 16%)

penetrating injury 9 (9/114, 8%)

Blunt injury 7 (7/114, 6%)

Injured solid organ, n (%) 58/114 (51%)

Liver

27 (27/58, 47%)

Spleen

21 (21/58, 36%)

adrenal gland

15 (15/58, 26%)

Kidney

13 (13/58, 22%)

Pancreas

4 (4/58, 7%)

Testis

Actively bleeding patients, n (%)

1 (1/58, 2%)

48/114(42%)

Angiography and embolization 33 (33/48, 69%)

Branches of internal iliac artery 14 (14/33, 42%)

Hepatic artery and inferior phrenic artery 10 (10/33, 30%)

Splenic artery 9 (9/33, 27%)

Renal artery 7 (7/33, 21%)

Surgery 13 (13/48, 27%)

Mesentery 5 (5/13, 38%)

Small bowel 2 (2/13, 15%)

Liver 2 (2/13, 15%)

Spleen 2 (2/13, 15%)

Stomach 1 (1/13, 8%)

Colon 1 (1/13, 8%)

No treatment 2 (4%)

Contained vascular injuries 8/114(7%)

Angiography and embolization 7 (7/8, 87%)

Hepatic artery and inferior phrenic artery 3 (3/7, 42%)

Splenic artery 2 (2/7, 29%)

Renal artery 2 (2/7, 29%)

Surgery 1 (1/8, 13%)

Spleen 1 (1/1, 100%)

Table 2

Diagnostic performance of each CT phase for detecting active bleeding.

Readers

CT Phase

Sensitivity (%)

Specificity (%)

AUC

95% CI

p-Value

Reader 1

Arterial

93.5

91.1

0.923

0.858, 0.965

b0.001

Portal

95.7

91.2

0.934

0.872, 0.972

b0.001

Combined

95.7

89.7

0.927

0.863, 0.967

b0.001

Reader 2

Arterial

91.3

91.2

0.912

0.845, 0.957

b0.001

Portal

91.3

91.2

0.912

0.845, 0.957

b0.001

Combined

95.7

91.2

0.934

0.872, 0.972

b0.001

Reader 3

Arterial

89.1

89.7

0.894

0.823, 0.944

b0.001

Portal

89.1

94.1

0.916

0.849, 0.960

b0.001

Combined

91.3

89.7

0.905

0.836, 0.952

b0.001

Pool

Arterial

91.3

90.7

0.910

0.874, 0.938

b0.001

Portal

92.0

92.2

0.921

0.887, 0.947

b0.001

Combined

94.2

90.2

0.922

0.888, 0.948

b0.001

Note – CI = confidence interval.

software (MedCalc Software bvba, Ostend, Belgium) for analysis, and p– values of b0.05 were considered statistically significant.

Results

Patient demographics and clinical presentations of the study popula- tion are shown in Table 1. Patients included 82 men and 32 women, with ages ranging from 16 to 92 years (mean age, 47.2 years). Traffic collision were the most common cause of injury (n = 79, 70%). All penetrating in- juries were Stab wounds (n = 9, 8%). Blunt injuries included those resulting from violence, or Crush injury by heavy machinery equipment or forklift truck. Forty-eight patients (48/114, 42%) had active bleeding in the abdominal cavity. Thirty-three patients (33/48, 69%) received transcatheter arterial embolization, and thirteen patients (13/48, 27%) underwent surgical exploration. Contained vascular injuries, including pseudoaneurysms or arteriovenous fistulas, were seen in8 of the 114 pa- tients (7%). Six patients (6/8, 75%) received transcatheter arterial embo- lization and 2 patients (2/8, 25%) underwent surgical exploration.

Diagnostic performance

The results of diagnostic performance of arterial, portal venous, and combined phase CT with regard to detecting active bleeding are pre- sented in Table 2. The diagnostic AUC of the three readers ranged from 0.894 to 0.934. Pooled data showed an AUC of 0.910, 0.921 and 0.922 for arterial, portal venous, and combined phase CT, respectively (p b 0.001). There was no significant differences between the diagnostic performance of arterial, portal venous, and combined phase CT in terms of detecting active bleeding (p N 0.112). Missed cases for detecting ac- tive bleeding at the arterial, portal, and combined phases were five, six, and four cases, respectively, by all readers. These cases were reassessed by two abdominal and interventional radiologists (H.S.K

and J.H.K, with 25 and 16 years of experience, respectively) who did not participate as readers. They judged that participant readers misinterpreted the active bleeding in one case in the arterial and three cases in the portal phase. In another case, active bleeding occurred only in the portal phase. However, since the bleeding was confined to the abdominal wall with stable vital signs, they judged that this patient could be treated using conservative management sufficiently. Another one case showed severe liver injuries (American Association for the Surgery of Trauma, AAST Grade V) with hepatic infarction in both lobes of liver. However, active Bleeding focus was equivocal in both CT phases. The patient received surgical treatment regardless of active bleeding. Hence, it is likely that there was discordant interpretation between readers with regard to active bleeding in this case. In the re- maining two cases, there was no visible active bleeding in both arterial and portal phases.

The results for diagnostic performance of the arterial, portal venous, and combined phase CT with regard to detecting contained vascular in- juries are presented in Table 3. Contained vascular injuries were seen in 8 of the 114 patients (7%). The diagnostic AUC of the three readers ranged from 0.643 to 0.803. Pooled data showed an AUC of 0.723, 0.643, and 0.723 for arterial, portal venous, and combined phase CT, respectively (p b 0.003). The arterial or combined phase and portal ve- nous phase of pooled data showed only slightly significant diagnostic performance (p = 0.039). Missed cases for detecting contained vascular injuries at arterial, portal, and combined phases were five each, respec- tively, by all readers. These cases were reassessed by two radiologists (H.S.K and J.H.K). In two cases, there were discordant interpretations with regard to contained vascular injuries between participant readers. These two cases showed severe liver injuries (AAST Grade V) with hepatic infarction in both lobes of liver. However, contained vascular in- juries were equivocal at both CT phases. The patient received surgical treatment regardless of active bleeding. Hence, it was likely that there

Table 3

Diagnostic performance of each CT phase for detecting contained vascular injuries.

Readers

CT Phase

Sensitivity (%)

Specificity (%)

AUC

95% CI

p-Value

Reader 1

Arterial

62.5

98.1

0.803

0.718, 0.872

0.001

Portal

37.5

99.1

0.683

0.589, 0.767

0.046

Combined

62.5

98.1

0.803

0.718, 0.872

0.001

Reader 2

Arterial

37.5

100

0.688

0.594, 0.771

0.04

Portal

37.5

100

0.688

0.594, 0.771

0.04

Combined

37.5

100

0.688

0.594, 0.771

0.04

Reader 3

Arterial

50

98.1

0.741

0.650, 0.818

0.011

Portal

37.5

99.1

0.683

0.589, 0.767

0.046

Combined

50

99.1

0.741

0.650, 0.818

0.011

Pool

Arterial

45.8

98.7

0.723

0.672, 0.770

b0.001

Portal

29.1

99.4

0.643

0.589, 0.694

0.003

Combined

45.8

98.7

0.723

0.672, 0.770

b0.001

Note – CI = confidence interval.

Table 4

Diagnostic performance of each CT phase for detecting organ injuries.

Readers

CT Phase

Sensitivity (%)

Specificity (%)

AUC

95% CI

p-Value

Reader 1

Arterial

98.2

93.3

0.957

0.915, 1.000

b0.001

Portal

96.3

93.3

0.948

0.901, 0.995

b0.001

Combined

96.3

93.3

0.948

0.901, 0.995

b0.001

Reader 2

Arterial

96.3

93.3

0.948

0.901, 0.995

b0.001

Portal

96.3

93.3

0.948

0.901, 0.995

b0.001

Combined

96.3

93.3

0.948

0.901, 0.995

b0.001

Reader 3

Arterial

96.3

93.3

0.948

0.901, 0.995

b0.001

Portal

96.3

93.3

0.948

0.901, 0.995

b0.001

Combined

96.3

93.3

0.948

0.901, 0.995

b0.001

Pool

Arterial

96.9

93.3

0.951

0.925, 0.977

b0.001

Portal

96.3

93.3

0.948

0.921, 0.977

b0.001

Combined

96.3

93.3

0.948

0.921, 0.977

b0.001

Note – CI = confidence interval.

were discordant interpretations with regard to contained vascular injuries of the case between readers. In the remaining three cases, there were no visible active bleeding at both arterial and portal phases. The results for diagnostic performance of arterial, portal venous, and combined phase CT with regards to detecting organ injuries are pre- sented in Table 4. The diagnostic AUC of the three readers ranged from 0.948 to 0.957. Pooled data showed an AUC of 0.951, 0.948, and 0.948 for arterial, portal venous, and combined phase CT, respectively (p b 0.001). There was no significant difference between the diagnostic performance of arterial, portal venous, and combined phase CT in terms of detecting organ injuries (p N 0.317). Only six patients received surgery for organ injury, without visible active bleeding on CT. Two patients had a large Liver laceration, two patients had a large kidney laceration, and two patients had diaphragmatic rupture. Missed cases for detecting Solid organ injuries at arterial, portal, and combined phases were two each, respectively, by all readers. These cases were reassessed by two radiologists (H.S.K and J.H.K). In two cases, there were discordant interpretations between participant readers with re- gard to organ injuries. These two cases showed suspicious subcapsular low density lesions in liver at both arterial and portal phases, and follow-up CT revealed that these lesions were decreased. They were judged as liver injuries (AAST Grade I), and these patients were not

needed any additional interventions.

Estimation of cED and LAR values

The cED of each CT phase is presented in Table 5. The average cEDs of 114 patients exposed to arterial and portal venous phase abdominal CT were 8.835 mSv (median, 7.575 mSv; interquartile range [IQR], 5.95-11.30 mSv) and 9.305 mSv (median, 8.108 mSv; IQR, 6.31-11.77 mSv), respectively. The estimated mean LARs for cancer incidence and mortality with arterial phase CT were 0.059% (median, 0.050%; IQR, 0.03-0.07%) and 0.034% (median, 0.027%; IQR,

0.02-0.04%), respectively (Table 6). In portal venous phase CT, the estimated mean LARs for cancer incidence and mortality were 0.062% (median, 0.053%; IQR, 0.03-0.08%) and 0.036% (median, 0.030%; IQR,

0.02-0.04%), respectively. In combined phase CT, the estimated mean

LARs for cancer incidence and mortality were 0.121% (median, 0.104%; IQR, 0.06-0.15%) and 0.070% (median, 0.057%; IQR, 0.04-0.08%),

respectively.

Discussion

In this study, we found that the diagnostic performance of combined phase CT, with regards to detecting active bleeding, did not show a sig- nificant advantage compared to diagnosis using single (arterial or portal venous) phase CT protocol. For all CT protocols, the sensitivities and specificities were N90%, and each protocol had an AUC N0.9. We found that there was no significant difference in diagnostic performance be- tween two CT protocol sets (arterial vs portal venous, arterial vs com- bined, portal venous vs combined), with regards to active bleeding.

In the Pooled analysis, arterial and combined CT phases were slightly superior for identification of contained vascular injuries, compared to portal venous phase CT; however, the small sample size limits generali- zation of results. The detection of pseudoaneurysm is important because these injuries have an unfavorable outcome with conservative manage- ment. Pseudoaneurysms are associated with an increased incidence of overt bleeding necessitating blood transfusions, increased mortality with associated infection, and Delayed diagnosis and treatment [18,22]. Previous studies have shown that contained vascular injuries are identi- fied more accurately at the arterial phase of image acquisition compared to portal venous phase, in more than half of these cases [1,8].

Combined arterial and portal venous phase CT, is being commonly used to evaluate patients with Abdominal hemorrhage or organ damage in the emergency and trauma departments for rapid and accurate diag- nosis. However, physicians should not forget that the higher the num- ber of CT phases, the greater the patient’s exposure to radiation. Therefore, it is important to reduce the number of CT phases exposures as much as possible. In order to solve this problem, we have studied the diagnostic performance of two single phase CTs (arterial and portal ve- nous phase) and combined phase CT, and compared the performance of each phase.

Table 5

Table 6

Average LAR of cancer incidence and mortality for each CT phase.

Average cED of each CT phase.

CT phase

Incidence (%)

p-Value

Mortality (%)

p-Value

CT phase

cED (mSv) [IQR]

p-Value

[IQR]

[IQR]

Arterial Portal venous Combined

Arterial vs. portal

8.835 [5.95-11.30]

9.305 [6.31-11.77]

18.140 [12.20-22.97]

0.186

Arterial Portal venous Combined

Arterial vs. portal

0.059 [0.03-0.07]

0.062 [0.03-0.08]

0.121 [0.06-0.15]

0.327

0.034 [0.02-0.04]

0.036 [0.02-0.04]

0.070 [0.04-0.08]

0.287

Arterial vs. combined Portal vs. combined

b0.001 b0.001

Arterial vs. combined Portal vs. combined

b0.001 b0.001

b0.001 b0.001

Note -cED = cumulative effective dose, IQR = interquartile range. Note -LAR = lifetime attributable risks, IQR = interquartile range.

The cED was significantly reduced with single phase CT used alone compared to combined phase CT. Projected cancer incidence and mortality were also significantly lower with single phase pro- tocol. According to the linear no-threshold theory [22], for single phase CT, exposure was estimated to result in a lifetime excess risk of 34 cancers per 100,000 patients, and for the biphasic CT, the estimated risks were 59 cancers per 100,000 patients. These re- sults predict that the use of biphasic CT at the age of 45 years caused one additional cancer in an estimated 4000 patients as com- pared single phase CT. For the solution of high dose radiation expo- sure in patients with trauma, radiologists and physicians have strived to apply optimal CT protocol to reduce radiation dose while maintaining good Image quality. Yaniv et al. reported that re- vised single phase body CT showed better vascular and abdominal parenchymal imaging with reduction in radiation dose, compared with conventional protocol in patients with trauma [20]. Single phase protocol decreased mean (+-standard deviation, SD) effec- tive radiation dose from 18.2 +- 8.2 mSv to 12.4 +- 4.4 mSv. These results predict that the use of conventional CT at the age of 40 years caused one additional cancer in an estimated 2500 pa- tients as compared with single phase CT. However, this study did not compare diagnostic performance of active bleeding or abdom- inal organ injury between the two protocols. Alagic et al. demon- strated that multiphase low-radiation protocol improved diagnostic accuracy of arterial injuries with reduced radiation [19]. Low-radiation protocol decreased mean (+-SD) effective radi- ation dose from 1932 +- 247 mGy * cm to 1681 +- 183 mGy * cm,

compared with conventional single phase CT. These results predict

that the use of conventional CT at the age of 45 years caused one additional cancer in an estimated 5000 patients as compared with low-dose CT. On the basis of these studies, further studies on opti- mization of CT such as single phase low-radiation dose CT protocol for use in patients with trauma are expected in future.

The role of emergency physicians is important for radiation dose reduction in traumatic injury patients who visit the emer- gency department. Considerable number of young adults undergo traumatic injury, and trauma patients frequently need whole body CT scans. It is generally accepted that younger patients are more susceptible to carcinogenesis associated with radiation [17,24-26] From the recent survey, emergency physicians have greater interest in radiation dose reduction, and would like to dis- cuss cancer risk with their patients. Concerns of cancer risks from radiation will increase the applicability of using single phase CT to the ordering physicians [27].

Our study has some limitations. The small sample size of contained vascular injuries limits the conclusions that may be drawn from this study, and reduces the statistical power of our re- sults. Secondly, we included only the patients who underwent both phases of CT scan. Dual phase CT is performed in patients with se- vere injuries, but minor trauma patients usually undergo single phase CT scan. This population is not representative of all patients with trauma, and hence, there is a selection bias.

In conclusion, single phase CT could be a potential protocol for abdominal trauma patients. Use of single phase CT could significantly decrease the incidence of radiation-associated cancer in the future.

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