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Published online before print November 17, 2005, 10.1148/radiol.2381050489

(Radiology 2005;238:135.)

A more recent version of this article appeared on December 1, 2005
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© RSNA, 2005

Gastrointestinal Imaging

Small-Bowel Obstruction: Coronal Reformations from Isotropic Voxels at 16-Section Multi–Detector Row CT1

Tracy A. Jaffe, MD, Lucie C. Martin, MD, John Thomas, MD, Andrew R. Adamson, MD, David M. DeLong, PhD and Erik K. Paulson, MD

1 From the Department of Radiology, Duke University Medical Center, Erwin Rd, Box 3808, Durham, NC 27710. Received March 23, 2005; revision requested May 13; revision received June 23; final version accepted July 18. Supported in part by GE Healthcare. Address correspondence to T.A.J. (e-mail: jaffe002{at}mc.duke.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Purpose: To retrospectively assess the added value of coronal reformations of the abdomen and pelvis from isotropic voxels by using 16-section multi–detector row computed tomography (CT) for the diagnosis of small-bowel obstruction (SBO).

Materials and Methods: This HIPAA-compliant study was approved by the institutional review board of this medical center with a waiver of informed consent. One hundred consecutive patients (40 men and 60 women; mean age, 55 years) suspected of having SBO and abdominal pain underwent 16-section multi–detector row CT with coronal reformations. Twenty-nine patients had a final diagnosis of SBO, and 71 patients did not. Three independent readers blinded to the diagnosis interpreted the CT scout scan, then transverse scans alone, and then transverse plus coronal scans for the presence of SBO and abnormal wall enhancement. Confidence was scored with a 1–5 scale (1 = absent, 5 = present).

Results: Mean sensitivity and specificity of CT scout alone, transverse CT alone, and transverse plus coronal CT for the diagnosis of SBO were 88% and 86%, 87% and 87%, and 87% and 90%, respectively (not significant). In patients without SBO, transverse plus coronal CT enhanced confidence in the exclusion of SBO (P = .01). In patients with SBO, transverse plus coronal CT enhanced confidence in the diagnosis of SBO and identification of abnormal wall enhancement (P = .01).

Conclusion: Transverse 16-section multi–detector row CT data sets are an excellent test for the diagnosis of SBO, while the addition of coronal reformations obtained from these isotropic data sets adds confidence to the diagnosis and exclusion of SBO.

© RSNA, 2005


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Small-bowel obstruction (SBO) is a common cause of abdominal pain, accounting for up to 20% of all admissions for acute abdomen (1–6). While abdominal radiography is often still the preferred initial radiologic examination of symptomatic patients with SBO (7,8), computed tomography (CT) has gained favor because it can more consistently help determine the presence or absence of obstruction, as well as the cause, severity, and transition point of obstruction. In addition, CT can reliably depict secondary signs of bowel obstruction, such as abnormal wall thickening or enhancement, ascites, and pneumatosis. Reported sensitivity of CT for high-grade SBO is 90%–96%, with a specificity of 91%–96% and accuracy of 90%–95% (1,5,9–14). CT is reported to be less accurate in patients with low-grade or partial SBO (1,11–14).

Determining the point of transition of SBO and the severity of the obstruction is critical because this information can guide patient care. Finding the transition point can be difficult at times, especially in patients with markedly dilated loops or a paucity of intraabdominal fat (15). It has been suggested that multiplanar reformatted scans may be helpful in identification of this zone of transition (15–17). However, to our knowledge, no studies have helped determine the value of these reformatted scans.

With 16-section multi–detector row CT, it is now possible to scan the entire abdomen and pelvis within a single and comfortable breath hold at a resolution of less than 1 mm in the x, y, and z axes (18,19). These data sets result in voxels that are both submillimeter in dimension and isotropic, which suggests that reformations in any desired plane will have spatial resolution similar to that in the transverse plane (20).

Thus, the purpose of our study was to retrospectively assess the added value of coronal reformations of the abdomen and pelvis from isotropic voxels by using 16-section multi–detector row CT for the diagnosis of SBO.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Patients and Diagnosis
This retrospective, Health Insurance Portability and Accountability Act-compliant study was approved by the institutional review board of this medical center with a waiver of informed consent. The study was supported in part by GE Healthcare, who provided research technologist financial support. However, the authors had full control of the data and information included in the manuscript.

From June 1, 2003, to February 1, 2004, 100 consecutive patients with abdominal pain underwent 16-section multi–detector row CT to rule out suspected SBO. The medical records, surgical reports, and pathologic reports were reviewed (T.A.J.) to determine the diagnosis. The diagnosis of SBO (n = 29) was made if the patient had surgical proof or had relief of obstructive symptoms after a trial of bowel rest and nasogastric tube suction. The exclusion of SBO was made if an alternative diagnosis was established and treated (n = 45) or if the patient did not undergo exploratory laparotomy and had no evidence of persistent pain, abscess, or unexplained fever during the hospital stay (n = 26). Of the 100 patients who underwent scanning, 60 were women and 40 were men. The mean patient age was 55 years (range, 21–94 years).

Scanning
Scanning was performed from the dome of the diaphragm through the pubic symphysis with a CT scanner (LightSpeed 16; GE Healthcare, Milwaukee, Wis). Patients ingested 450 mL of a 2% barium sulfate suspension (Readi-Cat 2; E-Z-Em, Westbury, NY) 1–2 hours before scanning. Iopamidol, 150 mL (Isovue [300 mg of iodine per milliliter]; Bracco Diagnostics, Princeton, NJ), was injected at a rate of 3 mL/sec. Eighty-eight patients received the oral contrast agent, and 89 received the intravenous contrast agent. Imaging was performed during the portal venous phase as determined with bolus tracking and automated triggering technology. The protocol was as follows: 140 kVp; 350 mA; 16 x 0.625 mm detector configuration; pitch, 1.75; table speed, 17.5 mm per rotation; and gantry speed, 0.5 second per rotation. The transverse section data were reconstructed twice: first with 5-mm-thick sections at 5-mm intervals in the transverse plane and then with 0.625-mm-thick sections at 0.625-mm intervals. The second set of reconstructed transverse scans was then reformatted in the coronal plane with a thickness of 3 mm at 5-mm intervals.

The reconstructions were performed with a commercially available console system devoted to rapid reconstruction (Xtream; GE Healthcare) and that consists of dual 2.66-GHz processors (Xenon; Intel, Santa Clara, Calif) with a CT scan generator capable of reconstructing six to 10 scans per second. The scan generator required approximately 2 minutes to reconstruct both transverse and coronal scans. The entire process was performed by the technologist at the operator's console. The 5-mm-thick transverse and 3-mm-thick coronal scans were transferred to a picture archiving and communication system (PACS) workstation (Centricity 1.0; GE Healthcare) as a separate series of scans for interpretation.

Scan Evaluation
The CT scans were anonymized and loaded onto a workstation (Advantage Windows; GE Healthcare) for review. This included the CT scout scan, the transverse series, and the coronal reformatted series. Three readers (L.C.M., J.T., E.K.P.) with subspecialty training in CT imaging of the abdomen served as independent readers blinded to the diagnosis. The three readers had 1, 4, and 14 years of experience dedicated to CT of the abdomen. Readers were first asked to evaluate the CT scout scan and determine whether an SBO was present. The readers then scored the transverse scans alone and then immediately scored the coronal scans from the same patient. Impressions from the transverse scans were fresh in the minds of the readers. For both the transverse and coronal data sets, readers rated the scans for ability to identify the site and cause of SBO, as well as the findings of obstruction, including small-bowel wall thickening, pneumatosis, ascites, and abnormal wall enhancement. A confidence score for each of the preceding findings was obtained with a 1–5 scale as follows: score of 1 = SBO definitely absent, score of 2 = SBO probably absent, score of 3 = cannot determine SBO, score of 4 = SBO probably present, and score of 5 = SBO definitely present. For the diagnosis of SBO, a score of 4 or 5 was considered affirmative.

Statistical Analysis
The sensitivity and specificity of each reader were determined for the scout CT scan, as well as the transverse scans alone and the transverse plus coronal scans. P values for comparisons of the average reader sensitivity and specificity between transverse scans alone and transverse plus coronal scans were computed by means of the signed rank test. P values for comparisons of reader-specific values were computed by means of the McNemar test. For the purpose of this study, P < .05 was considered to indicate a significant difference.

Agreement between readers for the diagnosis of SBO on the basis of transverse scans and transverse plus coronal scans was determined by using the {kappa} statistic. The difference in the average {kappa} values between the transverse and transverse plus coronal scans was assessed by means of the jackknife method. The mean confidence ratings of each finding of SBO were classified according to reader, diagnosis, and transverse and coronal scans. Differences in ratings were determined by using the Wilcoxon signed rank test. The area under the receiver operating characteristic (ROC) curve was established for both the transverse and the transverse and coronal scans combined. These values, based on the Wilcoxon-Mann-Whitney statistic, were given for the three readers. Statistical software (SAS system, version 8.2; SAS Institute, Cary, NC) was used.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 
Diagnosis of SBO
On the basis of the CT scout view alone, readers 1, 2, and 3 identified an SBO in 38, 34, and 35 patients, respectively. The mean number of patients in which SBO was identified for all three readers was 36. This leads to a mean sensitivity of 88% and a mean specificity of 86% (Table 1). There was agreement between the readers ({kappa} = 0.66). There was no significant difference in sensitivity or specificity between transverse scans and transverse plus coronal scans for any reader (Table 1).


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  		Table 1. Sensitivity and Specificity for Diagnosis of SBO

 
Reader Agreement
For the transverse scans alone, there was good agreement ({kappa} range, 0.72–0.75) among all three readers (Table 2). For the transverse plus coronal scans, the {kappa} values (range, 0.78–0.84) were even greater, indicating a higher level of agreement for the transverse plus coronal scans than for the transverse scans alone. This difference was significant (P = .027).


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  		Table 2. Agreement among Readers for Diagnosis of SBO

 
Confidence Score for Imaging Findings and SBO
For patients without SBO, the confidence scores for the absence of SBO for each reader and the mean of the three readers showed that for the transverse and coronal scans, readers were more confident in the absence of obstruction than for the transverse scans alone (Table 3). This difference was significant (P < .001).


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  		Table 3. Mean Confidence Scores for 71 Patients without SBO

 
For patients with SBO (Table 4), the confidence scores for the presence of SBO for each reader and the mean of the three readers showed that for the transverse plus coronal scans, readers were more confident in the presence of SBO than for the transverse scans alone (Figs 1 –3).


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  		Table 4. Mean Confidence Scores in 29 Patients with SBO

 


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  		Figure 1a: CT scans in a 78-year-old woman with acute abdominal pain. (a) Transverse CT scan obtained with intravenous and oral contrast agents shows dilated proximal small-bowel loops. (b) Coronal reformation shows dilated small-bowel loops with a transition point (arrow) in the midabdomen.

 


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  		Figure 1b: CT scans in a 78-year-old woman with acute abdominal pain. (a) Transverse CT scan obtained with intravenous and oral contrast agents shows dilated proximal small-bowel loops. (b) Coronal reformation shows dilated small-bowel loops with a transition point (arrow) in the midabdomen.

 


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  		Figure 2a: CT scans in a 36-year-old woman with a 36-hour history of nausea and vomiting. (a) Transverse CT scan obtained with intravenous and oral contrast agents demonstrates multiple dilated loops of proximal small bowel (black arrow) with inflammatory mass (white arrow) in right lower quadrant, in the region of the cecum. (b) Coronal CT scan shows small-bowel dilatation leading to an inflammatory mass involving the cecum. The point of obstruction (arrow) is at the level of the cecum. Examination of subsequent biopsy specimen of this mass demonstrated adenocarcinoma.

 


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  		Figure 2b: CT scans in a 36-year-old woman with a 36-hour history of nausea and vomiting. (a) Transverse CT scan obtained with intravenous and oral contrast agents demonstrates multiple dilated loops of proximal small bowel (black arrow) with inflammatory mass (white arrow) in right lower quadrant, in the region of the cecum. (b) Coronal CT scan shows small-bowel dilatation leading to an inflammatory mass involving the cecum. The point of obstruction (arrow) is at the level of the cecum. Examination of subsequent biopsy specimen of this mass demonstrated adenocarcinoma.

 


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  		Figure 3a: CT scans in a 50-year old man with severe abdominal pain and no fever. (a) Transverse CT scan of upper abdomen obtained with intravenous and oral contrast agents shows multiple dilated loops of proximal small bowel. (b) Transverse CT scan in the pelvis shows decompressed loops (arrow) of distal small bowel. The caliber change indicates an SBO. (c) Transverse CT scan obtained at the level of pubic symphysis shows incarcerated small bowel in right inguinal hernia (arrow). (d) CT coronal reformation shows the incarcerated small-bowel loop (arrow) in the right groin. This is the level of the transition point, and all readers were confident of the diagnosis of SBO on both transverse and coronal scans.

 


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  		Figure 3b: CT scans in a 50-year old man with severe abdominal pain and no fever. (a) Transverse CT scan of upper abdomen obtained with intravenous and oral contrast agents shows multiple dilated loops of proximal small bowel. (b) Transverse CT scan in the pelvis shows decompressed loops (arrow) of distal small bowel. The caliber change indicates an SBO. (c) Transverse CT scan obtained at the level of pubic symphysis shows incarcerated small bowel in right inguinal hernia (arrow). (d) CT coronal reformation shows the incarcerated small-bowel loop (arrow) in the right groin. This is the level of the transition point, and all readers were confident of the diagnosis of SBO on both transverse and coronal scans.

 


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  		Figure 3c: CT scans in a 50-year old man with severe abdominal pain and no fever. (a) Transverse CT scan of upper abdomen obtained with intravenous and oral contrast agents shows multiple dilated loops of proximal small bowel. (b) Transverse CT scan in the pelvis shows decompressed loops (arrow) of distal small bowel. The caliber change indicates an SBO. (c) Transverse CT scan obtained at the level of pubic symphysis shows incarcerated small bowel in right inguinal hernia (arrow). (d) CT coronal reformation shows the incarcerated small-bowel loop (arrow) in the right groin. This is the level of the transition point, and all readers were confident of the diagnosis of SBO on both transverse and coronal scans.

 


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  		Figure 3d: CT scans in a 50-year old man with severe abdominal pain and no fever. (a) Transverse CT scan of upper abdomen obtained with intravenous and oral contrast agents shows multiple dilated loops of proximal small bowel. (b) Transverse CT scan in the pelvis shows decompressed loops (arrow) of distal small bowel. The caliber change indicates an SBO. (c) Transverse CT scan obtained at the level of pubic symphysis shows incarcerated small bowel in right inguinal hernia (arrow). (d) CT coronal reformation shows the incarcerated small-bowel loop (arrow) in the right groin. This is the level of the transition point, and all readers were confident of the diagnosis of SBO on both transverse and coronal scans.

 
Overall, there was no significant difference in confidence scores in the comparison of transverse scans and transverse plus coronal scans with respect to the diagnosis of secondary signs of obstruction. The one exception was abnormal wall enhancement, for which the difference in confidence scores was significant (P = .008).

Area under the ROC Curve
There was no significant difference in the area under the ROC curve between the two readings with respect to the diagnosis of SBO. The mean area under the ROC curve was 0.953 ± 0.023 for the transverse scans alone and 0.956 ± 0.016 for the transverse plus coronal scans.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
ADVANCES IN KNOWLEDGE
 References
 
While multiplanar reformations may be performed by using four-section multi–detector row CT, scan quality was restricted by limited z-axis resolution and longer acquisition times. These reformations were degraded by motion and stairstep artifacts (21). Current use of submillimeter isotropic data sets with 16-section multi–detector row CT has proved advantageous in cardiac, pulmonary, and musculoskeletal imaging by facilitating the delineation of coronary bypass grafts, pulmonary abnormalities, and complex skeletal fractures (22–27). These technological advances have stimulated interest in many applications with respect to the abdomen and pelvis. Recent reports (28–31) indicate that multi–detector row CT urography with multiplanar reformations is helpful in evaluation of the urinary tract. Paulson et al (32) proved that submillimeter coronal reformations add to the confidence level of readers for the diagnosis of acute appendicitis.

To our knowledge, no one has yet evaluated the role of the coronal reformation obtained from 16-section multi–detector row CT in the diagnosis of SBO. Caoili et al (16)and Furukawa et al (33) suggested that multiplanar reformations are helpful for the evaluation of SBO, particularly in the identification of the point of transition from dilated to decompressed bowel. Our study was designed to evaluate the contribution of the isotropic coronal multiplanar reformations in the diagnosis of SBO.

In our study, SBO was identified in 36% (36 of 100) of the CT scout scans, and there was agreement between readers. Abdominal radiography carries a reported sensitivity and specificity ranging from 55% to 85% for the diagnosis of SBO; our CT scout scan sensitivity of 85% and specificity of 93% are substantially higher (2,8,9,12). This may be due to our selected patient population, because the patients referred for CT are more likely to have an SBO than the general population of patients referred for abdominal radiography.

The sensitivity and specificity of the transverse plus coronal scans were similar to those of the transverse scans alone and ranged from 82% to 90% and from 80% to 94%, respectively. These results corroborate recent reports indicating that multi–detector row CT performed by using both intravenous and oral contrast agents is an accurate examination in patients suspected of having SBO. The reported sensitivity and specificity for high-grade SBO range between 90%–96% and 91%–96%, respectively (1,6,9,10). Overall, CT is less precise (reported accuracy, 48%–67%) for depicting low-grade SBO because changes in bowel caliber are more subtle with low-grade SBO (11,12,14). In our study, we did not specifically distinguish between high- and low-grade obstructions.

Our results suggest that the coronal plane serves as a useful addition to the transverse plane in patients suspected of having SBO. The value of the coronal reformations is apparent in measures of agreement and diagnostic confidence among independent observers. Specifically, agreement for the diagnosis of SBO among the three readers was consistently higher for the interpretations of transverse plus coronal scans than for the transverse scans alone.

In patients with or without SBO, there was a shift in the spread of the confidence scores for the three readers. That is, there was a movement toward the extremes in confidence; in the patients with SBO, confidence scores were higher for the transverse plus coronal interpretations than for the transverse interpretations alone. Similarly, in the patients without SBO, confidence scores for the diagnosis of SBO were lower for the transverse plus coronal interpretations, which indicates that the readers were more confident in the absence of findings on the coronal scans.

Despite a shift in the confidence scores toward the extremes with the addition of the coronal scan, there was no appreciable difference in the identification of the secondary signs of SBO. Specifically, the recognition of bowel wall thickening, pneumatosis, and ascites was similar despite the addition of the coronal scans. Only the identification of abnormal wall enhancement was statistically significant (P = .008). This suggests that the transverse data sets are adequate for the detection of the secondary signs of SBO and that the coronal reformations do not aid in the diagnosis of these findings.

Similarly, there was no significant difference in the area under the ROC curve when we compared the transverse scans alone with the transverse plus coronal scans. The area under the ROC curve is a measure of the probability that the perceived abnormality of the two scans will allow correct identification; the ideal area under the ROC curve is 1.0, and the worst-case scenario is 0.5 (34). The area under the ROC curve was 0.953 for the transverse scans alone and 0.956 for the transverse plus coronal scans; this finding suggests that transverse CT is an excellent test for the diagnosis of SBO and that the addition of coronal scans does not substantially improve this test.

We restricted our reformations to the coronal plane for several reasons. The course of small-bowel loops can be followed most readily in the coronal plane, and most of the colon can often be identified in a single coronal section. In addition, the coronal plane may be more intuitive for surgeons and radiologists because it is analogous to a frontal view of an abdominal radiograph. Finally, our protocol required no imaging manipulation by radiologists, either on the operator's console or at a dedicated three-dimensional workstation. In our clinical practice, the reformations are sent directly to a PACS workstation and appear as a separate series for interpretation.

The protocol described herein is used routinely in our clinical practice. The source transverse scans are reconstructed two times. The first set of reconstructions is in the transverse plane at 5-mm thickness at 5-mm intervals. For a typical patient, this series results in approximately 70–100 scans. For the second set of reconstructions, the 0.625-mm-thick scans are reconstructed at 0.625-mm intervals, resulting in approximately 560–800 scans (20,32). This series is not used for diagnostic purposes because of the very large number of scans and because noise is problematic as a result of the 0.625-mm section thickness. Rather, the second set of reconstructed transverse scans is reformatted in the coronal plane, 3 mm thick at 5-mm intervals, resulting in 50–75 scans per patient. In our practice, the 5-mm-thick transverse and coronal scans are sent to the PACS as a series for interpretation. The 0.625-mm-thick transverse scans are archived but are not interpreted or sent to the PACS.

The CT dose index of the 16-section multi–detector row CT protocol detailed here is equivalent to an analogous four-section multi–detector row CT (LightSpeed, GE Medical Systems) protocol with the following technical parameters: 140 kVp; 220 mA; 4 x 2.5 mm detector configuration; pitch, 1.5; table speed, 15 mm per rotation; gantry speed, 0.8 second per rotation; and reconstruction thickness, 5 mm (35). The effective dose equivalent is similar to that of an eight-section multi–detector row CT protocol with the following parameters: 140 kVp; 270 mA; 8 x 1.25 mm detector configuration; pitch, 1.675; table speed, 16.75 mm per rotation; and gantry speed, 0.5 second per rotation (20).

There were limitations to this project. Despite the inclusion of 100 patients in the study, the number of patients with SBO was rather small. In addition, not all patients with SBO had surgical proof of the diagnosis. Indeed, many patients with SBO are treated conservatively with bowel rest and nasogastric tube suction, and no surgical proof is obtained. Nevertheless, we considered the diagnosis to be present only when there was convincing clinical evidence of SBO.

Another potential limitation was that we did not ask readers to specifically measure bowel diameter to infer the degree of obstruction. Our rationale is that patients with chronic low-grade obstruction may have bowel diameters far greater than those seen in patients with acute high-grade obstruction. Neither did we ask the readers to quantify the grade of obstruction (low vs high grade).

It should be noted that the coronal scans were interpreted after the interpretation of the transverse scans. Impressions from the transverse scans were fresh in the minds of the interpreters. Such a design may bias the results in favor of the subsequent interpretation, in this case the coronal scans. Our intention was to demonstrate the value of the coronal reformations as an adjunct to the transverse scans alone, not as a stand-alone sequence; we believe that in most clinical settings, it is unlikely that radiologists would abandon the transverse scans in favor of the coronal scans alone.

In conclusion, we found transverse imaging with 16-section multi–detector row CT to be an excellent test for the diagnosis of SBO. The addition of coronal reformations from isotropic voxels is a valuable adjunct to the transverse scans in the evaluation of patients suspected of having SBO because it improves confidence levels in both identification and exclusion of bowel obstruction.


   ADVANCES IN KNOWLEDGE
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
References
 


   FOOTNOTES
 

Abbreviations: PACS = picture archiving and communication system • ROC = receiver operating characteristic • SBO = small-bowel obstruction

See Materials and Methods for pertinent disclosures.

Author contributions: Guarantor of integrity of entire study, T.A.J.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; approval of final version of submitted manuscript, all authors; literature research, T.A.J., L.C.M., J.T., E.K.P.; clinical studies, T.A.J., L.C.M., J.T., A.R.A., E.K.P.; statistical analysis, D.M.D.; and manuscript editing, all authors


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 ADVANCES IN KNOWLEDGE
 References
 

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