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DOI:10.2214/AJR.04.1762
AJR 2006; 187:1212-1221
© American Roentgen Ray Society


Pictorial Essay

MDCT of Small-Bowel Disease: Value of 3D Imaging

Seong Sook Hong1,2, Ah Young Kim1, Jae Ho Byun1, Hyung Jin Won1, Pyo Nyun Kim1, Moon-Gyu Lee1 and Hyun Kwon Ha1

1 Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, 388-1 Pungnap-dong, Songpa-gu, Seoul 138-736, Korea.
2 Present address: Department of Radiology, Soonchunhyang University Hospital, Seoul, Korea.

Received November 12, 2004; accepted after revision June 13, 2005.

 
Address correspondence to A. Y. Kim (aykim{at}amc.seoul.kr).


Abstract
Top
Abstract
Introduction
MDCT Protocol
Clinical Applications of MDCT
Summary
References
 
OBJECTIVE. Our objective is to show the various clinical applications of MDCT enterography for evaluating small-bowel disease, with a focus on the added value of 3D imaging.

CONCLUSION. MDCT and refined 3D imaging processes can offer a full examination of the small bowel as well as powerful information about the bowel and its surrounding structures.

Keywords: abdominal imaging • CT • MDCT • small bowel


Introduction
Top
Abstract
Introduction
MDCT Protocol
Clinical Applications of MDCT
Summary
References
 
In the evaluation of patients with suspected small-bowel disease, an accurate radiologic examination is important both for recognizing possible small-bowel disease and to help reliably document normal morphology. Small-bowel follow-through and enteroclysis are widely used for small-bowel imaging; however, these examinations provide only indirect information about the bowel wall and surrounding structures and are prone to problems caused by overlapping bowel loops.

To overcome the limitations of previous techniques, CT enteroclysis, a technique combining the advantages of enteroclysis and CT, has been extensively investigated [1, 2]. Although CT enteroclysis profits from excellent distention of the entire small bowel and precise evaluation of the extent of extraluminal disease, it has the major drawbacks of invasiveness and high radiation exposure. Recently, the role of wireless capsule endoscopy to assess small-bowel disease has been reported. The value of this technique is well documented for diagnosing obscure gastrointestinal bleeding and early Crohn's disease [3, 4]. However, problems with this technique include capsule obstruction by bowel strictures and battery failure in prolonged transit (battery life is approximately 7 hours). The technique may provide false-negative results if there is rapid peristalsis at a lesion site or if there is bowel angulation at a lesion that impairs the camera view [5, 6].

Currently, the availability of MDCT and the continuous refinement of the 3D imaging process have greatly expanded the utility of CT for evaluating patients with small-bowel disease. MDCT is now readily available and has advantages over classic helical CT in the imaging of the mesenteric vasculature and of the small bowel. We will show various clinical applications of MDCT enterography for evaluating small-bowel diseases, focusing on the added value of 3D imaging. In addition, the technical limitations and potential pitfalls in the interpretation of 3D imaging will be discussed.


MDCT Protocol
Top
Abstract
Introduction
MDCT Protocol
Clinical Applications of MDCT
Summary
References
 
MDCT scans were obtained with a 16-MDCT scanner (Somatom Sensation 16, Siemens Medical Solutions) using the following scanning parameters: collimation, 16 x 0.75 mm; table feed/rotation, 12 mm; slice width, 0.75 mm; volume pitch, 16; 120 kVp; and 165 mAs. Images were reconstructed at 1-mm intervals with a B30 soft-tissue algorithm.

At the beginning of the contrast-enhanced CT scan, 150 mL of nonionic iodinated contrast material (Ultravist 370 [iopromide], Schering) was injected IV through a 20-gauge cannula at 3 mL/s using an automated power injector. The delay between the start of contrast administration and the start of helical scanning was approximately 10 seconds to achieve the arterial phase (using the CARE bolus-triggering program [Siemens Medical Solutions]) and 72 seconds for the delayed phase. Images were obtained from the dome of the liver to the lower margin of the symphysis pubis during a single breath-hold.

To evaluate mesenteric ischemia and gastrointestinal bleeding, three-phase CT (unenhanced, arterial, and delayed phase) was performed without oral contrast material. However, the weighted CT dose index and the dose-length product accrued from one dynamic phase CT were 9.32 mGy and 526-529 mGy, respectively. Therefore, in patients with suspected small-bowel obstruction, inflammatory bowel disease, or neoplasm, a single CT scan or a two-phase CT scan (delayed phase or unenhanced phase or both) was obtained.


Figure 1
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Fig. 1A 56-year-old man with acute mesenteric ischemia. Emboli or thrombi are not definitively shown on axial arterial phase CT image.

 


Figure 2
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Fig. 1B 56-year-old man with acute mesenteric ischemia. Oblique coronal plane of volume-rendered image shows large embolus (thick arrow) and extensive vascular occlusion (arrowheads) along superior mesenteric artery and its branches, with multifocal renal infarction (thin arrows). Because this patient suffered from longstanding severe heart failure, mesenteric ischemia was conservatively managed with anticoagulant drugs.

 
To opacify obstructed bowel loops, we used an oral water-soluble contrast material (Gastrografin, [meglumine diatrizoate], Schering) that has been shown to be valuable for diagnosing bowel obstruction, perforation, and gastrointestinal fistulization. However, positive oral contrast material can obscure the opacified blood vessels or interfere with the detection of bowel-wall changes such as bowel-wall enhancement. Therefore, this contrast material should not be administered in such cases. Although positive oral water-soluble contrast material did not interfere with 3D imaging in our patients, we preferred to use water as a neutral oral contrast material in patients with suspected ischemia. Neutral oral contrast material, such as water or methylcellulose, is recommended for the diagnosis of mesenteric ischemia or acute inflammatory bowel disease.

Real-time interactive 3D imaging was created by using multiplanar reconstruction, volume rendering, maximum or minimal intensity projection or both, and surface shaded display techniques using a commercially available workstation (Leonardo, Siemens Medical Solutions). Postimaging processing was performed by one experienced abdominal radiologist and took approximately 15 minutes.


Clinical Applications of MDCT
Top
Abstract
Introduction
MDCT Protocol
Clinical Applications of MDCT
Summary
References
 
Mesenteric Ischemia
Thromboembolic occlusion is the most common cause of acute mesenteric ischemia, with the emboli mainly originating from the heart. The critical roles of CT are to detect ischemic changes in the affected bowel loops and mesentery and to determine the cause of ischemia. Bowel distention, bowel-wall thickening, mesenteric edema, and ascites are common CT findings in patients with mesenteric ischemia; however, these findings are nonspecific. CT findings such as splanchnic vascular occlusion, intramural gas, lack of bowel-wall enhancement, and multiorgan infarctions have been proposed as specific findings that suggest acute mesenteric ischemia. These findings are readily evident using MDCT (Figs. 1A, 1B, 2A, and 2B). Thickened small-bowel loops may show an absence of enhancement or, in some cases, delayed and persistent enhancement when compared with unaffected loops [7-9].


Figure 3
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Fig. 2A 43-year-old man with acute mesenteric ischemia. MDCT volume-rendered image of arterial phase clearly shows no evidence of arterial emboli.

 

Figure 4
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Fig. 2B 43-year-old man with acute mesenteric ischemia. Volume-rendered delayed phase image shows extensive thrombosis of superior mesenteric vein (arrowheads) and its tributaries with adjacent infarcted bowel segment (thin arrows). Development of periportal collateral vessels (thick arrow) is also noted. Patient underwent segmental resection of ileal bowel loops because of transmural infarction.

 
Mesenteric emboli and focal infarction of the affected bowel loops can be directly shown on an MDCT scan. Most emboli wedge at branch points in the mid to distal superior mesenteric artery (SMA), usually distal to the middle colic artery (Figs. 1A and 1B). Meanwhile, thrombosis is most likely to occur at or near the origins of the proximal mesenteric arteries (Figs. 3A and 3B). Mesenteric venous thrombosis is an uncommon (less than 15%) but potentially lethal cause of bowel ischemia [10]. There are several predisposing factors for mesenteric venous thrombosis [11]. The superior mesenteric vein (SMV) is involved in 95% of identified cases (Figs. 2A and 2B). Conversely, chronic mesenteric ischemia is primarily caused by atherosclerosis of the mesenteric arteries. Calcified atherosclerotic plaque in the aorta and its major branches can easily be observed on MDCT.


Figure 5
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Fig. 3A 36-year-old man with chronic mesenteric ischemia. Thick-slab volume-rendered image of contrast-enhanced MDCT dramatically shows small pseudoaneurysm (arrow) in proximal origin portion of superior mesenteric artery.

 

Figure 6
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Fig. 3B 36-year-old man with chronic mesenteric ischemia. On multiplanar reconstruction image, extensive thrombosis (arrowheads) is well shown yet is not evident on thick-slab volume-rendered image (A). These findings were consistently depicted on follow-up CT scans for 1 year without interval change (not shown).

 


Figure 7
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Fig. 4A 55-year-old man with intermittent abdominal pain. Initial contrast-enhanced CT scan shows partial opacification of tributary of superior mesenteric vein (arrow), mimicking mesenteric venous occlusion.

 


Figure 8
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Fig. 4B 55-year-old man with intermittent abdominal pain. Axial CT image of delayed phase reveals full opacification of this mesenteric venous structure (arrow), indicating pseudoocclusion by systemic hypotension.

 


Figure 9
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Fig. 5 56-year-old man with asymptomatic atherosclerotic plaque. On combined image of maximal intensity projection and surface shaded display, focal vascular narrowing of proximal superior mesenteric artery is observed because of small defect (arrow), suggesting atherosclerotic plaque. Similar multiple focal defects (arrowheads) are also seen along abdominal aorta, indicating underlying chronic atherosclerotic vascular disorder.

 


Figure 10
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Fig. 6 31-year-old woman with acute onset of mid upper abdominal pain and intestinal obstruction after blunt trauma. On volume-rendered image after ingestion of diluted water-soluble oral contrast medium, abrupt luminal narrowing (thin arrows) with distended proximal bowel loops is clearly identified in duodenum (D). Adjacent perienteric hematoma (H) is also shown with segmental duodenal wall thickening and perienteric infiltration (arrowheads) indicating posttraumatic change. Opacification of distal bowel loops also suggests incomplete bowel obstruction (thick arrow). S = stomach.

 


Figure 11
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Fig. 7 33-year-old man with acute postoperative small-bowel obstruction. Linear alignment of stricture sites (arrowheads) is shown on posterior view of thick-slab volume-rendered image obtained after digital removal of bone structures. These multifocal strictures, located along an imaginary perpendicular line, suggest presence of postoperative adhesive band that was confirmed at surgery.

 


Figure 12
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Fig. 8 Small-bowel obstruction in 46-year-old man who underwent segmental resection of ileum. Thick-slab volume-rendered image obtained after ingestion of diluted water-soluble oral contrast medium shows metallic surgical clips (arrows) and adjacent collapsed bowel loops (arrowheads), indicating transition point of small intestinal obstruction.

 


Figure 13
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Fig. 9 67-year-old woman with complete small-bowel obstruction. On thick-slab volume-rendered image of contrast-enhanced MDCT after ingestion of water-soluble oral contrast medium, complete bowel obstruction (O) at proximal jejunum is shown with masslike, multiconcentric bowel-wall thickening (arrows). In conjunction with hepatic metastases (arrowheads) and mesenteric lymphadenopathy, this masslike wall thickening indicates intussusception by intestinal metastasis. Sonography-guided biopsy of mesenteric node revealed distant metastasis from lung cancer.

 


Figure 14
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Fig. 10A 27-year-old man with acute intestinal obstruction. Thick-slab volume-rendered image obtained after ingestion of diluted water-soluble oral contrast medium shows markedly dilated small-bowel loops (S) with diffuse fold thickening, but passage of oral contrast medium is not interrupted or delayed through large intestine (L). No definite pathologic obstruction site is shown.

 


Figure 15
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Fig. 10B 27-year-old man with acute intestinal obstruction. Thin-slice volume-rendered image shows suspicious multifocal stenotic segments (arrows) along small intestine. Tentative diagnosis based on CT scan was low-grade small-bowel obstruction of unknown cause due to nonspecific findings. However, cause of small-bowel obstruction proved to be persimmon bezoar that was extracted just before CT. No abnormal small-intestine findings were detected on small-bowel follow-through examination 3 months later (not shown).

 
Nonocclusive mesenteric ischemia is a common cause of acute mesenteric ischemia and usually affects patients over 50 years old who have cardiac dysfunction [12]. The bowel changes are similar to those of occlusive mesenteric ischemia; however, abrupt arterial occlusion is not seen with nonocclusive mesentric ischemia.

Using MDCT to diagnose mesenteric ischemia does have some limitations. First, inadequate or nonopacified blood in the mesenteric vessels, which can be caused by hypovolemia or spasm, can lead to a falsepositive diagnosis (Figs. 4A and 4B). Second, although calcified atherosclerotic plaques in the mesenteric vessels, seen on MDCT, are common features in patients with chronic mesenteric ischemia, these plaques often can be observed at the origin of the mesenteric arteries in older individuals lacking clinical symptoms. On the other hand, the small intestine can appear normal in patients with chronic mesenteric ischemia (Fig. 5). Therefore, careful clinical correlation with the CT findings is essential in the evaluation of patients with suspected mesenteric ischemia.

Small-Bowel Obstruction
The small bowel is involved in 60-80% of cases of intestinal obstruction. Because of the possibility of strangulation, misdiagnosis or delayed diagnosis can result in lethal or life-threatening complications such as ischemia and perforation. Therefore, in patients with suspected small-bowel obstruction, the role of imaging is to determine the presence or absence of an obstruction; to identify the site, severity, and cause of an existing obstruction; and to detect the possible presence of strangulation [13-15].

Diagnosis of bowel obstruction depends on the identification of a transition zone with dilated proximal bowel loops. However, depiction of a definite transition zone is sometimes difficult because of overlapping dilated bowel loops when viewing only axial images. Similarly, it is often difficult to differentiate obstruction from adynamic ileus. In these situations, the easily accessible 3D imaging of MDCT may help to verify the site, level, and cause of the obstruction [16] (Fig. 6). In particular, 3D imaging can be helpful in evaluating indeterminate cases on the axial plane, such as volvulus or internal hernia. The additional use of positive oral contrast material can help to distinguish complete from incomplete bowel obstruction.

Strangulating obstruction is more common in closed-loop obstruction than in simple obstruction. In the assessment of strangulation, various CT findings such as thickening and increased attenuation of the affected bowel wall, serrated beaklike narrowing at the site of obstruction, target or halo sign, pneumatosis intestinalis, and gas in the portal veins have been reported to be suggestive of strangulation. Among these features, poor or absent enhancement of the bowel wall, a "serrated beak" sign, and an unusual course of mesenteric vasculature or whirl sign are more specific findings that have statistical significance [17]. Findings of haziness or obliteration of the mesenteric vessels, localized mesenteric fluid, and hemorrhage are seen in the mesentery attached to the ischemic bowel loops. These CT features can be observed using 3D imaging with MDCT. Advanced 3D imaging processing, such as slab volume rendering using MDCT, is more flexible than 2D multiplanar reconstruction and also makes it possible to display unlimited planes with markedly reduced artifacts (Figs. 7, 8, 9).


Figure 16
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Fig. 11A 35-year-old woman with relapsed active Crohn's disease. Thin-slab volume-rendered image provides excellent topographic information regarding perienteric abscess and fistulous tract formation (arrows) resulting from relapsed ileocecal Crohn's disease (IC). Deformed terminal ileum and cecum show strongly enhanced bowel walls, suggesting active inflammation.

 


Figure 17
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Fig. 11B 35-year-old woman with relapsed active Crohn's disease. Multiplanar reconstruction image using a minimal intensity projection clearly shows multidirectional fistulous tracts (arrowheads) and active abscesses (a).

 


Figure 18
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Fig. 12A 38-year-old man with longstanding Crohn's disease. Thick-slab volume-rendered image obtained after ingestion of diluted water-soluble oral contrast medium shows segmental bowel aggregation and multifocal strictures (dotted circle). Eccentric bowel-wall thickening with perienteric infiltration (arrows) is also seen along mesenteric border.

 


Figure 19
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Fig. 12B 38-year-old man with longstanding Crohn's disease. Thick-slab volume-rendered image with a surface shaded display shows longitudinal linear ulcerations along mesenteric border (arrows) of multifocal small intestines and pseudosacculations (arrowheads).

 


Figure 20
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Fig. 13A 43-year-old woman with malignant gastrointestinal stromal tumor arising from jejunum. Coronal thick-slab volume-rendered image shows well-demarcated, exophytic growing mass (arrows) with large central ulceration originating from jejunum (J).

 


Figure 21
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Fig. 13B 43-year-old woman with malignant gastrointestinal stromal tumor arising from jejunum. Thick-slab volume-rendered image mimicking maximum intensity projection shows tumor-supplying mesenteric branches (thin arrows) of superior mesenteric artery and enlarged draining veins (arrowheads) from mass (thick arrows).

 
Using MDCT to diagnose small-bowel obstruction also has some limitations. False-positive diagnosis of the obstruction site is frequently caused by incomplete luminal distention owing to overly rapid passage or transient luminal narrowing caused by peristaltic movement (Figs. 10A and 10B). Conventional CT has poor sensitivity for low-grade small-bowel obstruction. CT enteroclysis may be considered in patients suspected to have such an obstruction.

Inflammatory Bowel Disease
For a long time, small-bowel series and enteroclysis have had a primary role in the diagnosis and management of patients with suspected inflammatory bowel disease of the small intestine. However, these imaging techniques do not offer any important information about extraluminal extension of the disease or changes in surrounding structures. CT can overcome this limitation, but its effectiveness is limited because it lacks both the ability to depict fine mucosal change of the affected bowel and to depict and localize a potential fistulous tract or bowel perforation. In some complex cases, such as Crohn's disease, the exact evaluation of the disease extent or stricture segment may be difficult to identify if only axial images are reviewed [18].

In evaluating bowel inflammation complicated by fistula or abscess, as seen in Crohn's disease or tuberculosis, 3D imaging may be helpful in understanding the full extent of disease (Figs. 11A and 11B). Three-dimensional volume rendering of MDCT performed with positive oral contrast material can improve visualization of the presence and site of both the stricture and the fistula (Figs. 12A and 12B). This valuable information from 3D CT may significantly improve the observer's confidence in interpreting the imaging and the clinician's or surgeon's understanding of the extent of the disease.

Among the limitations of using MDCT to diagnose inflammatory bowel disease are that to obtain proper 3D information, optimal distention of the entire small intestine is essential. Although positive oral contrast material is valuable for diagnosing bowel obstruction, perforation, and fistulization, evaluation for bowel-wall enhancement after injection of IV contrast material can be limited because of the partial volume averaging effect. From this point of view, the use of negative oral contrast material, such as water or methylcellulose, can be considered in early active change of inflammatory bowel disease.


Figure 22
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Fig. 14 37-year-old man with obscure gastrointestinal bleeding. In this patient, two attempts at RBC scans yielded negative results. This coronal maximum-intensity-projection image obtained from arterial phase of MDCT shows direct extravasation of contrast material into proximal jejunal loop (arrow). At surgery, bleeding focus was confirmed to be angiodysplasia of proximal jejunum.

 


Figure 23
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Fig. 15A 55-year-old man with obscure gastrointestinal bleeding. Axial CT image obtained from arterial phase MDCT shows highly enhanced, tortuous vascular structure (arrows) along bowel wall of distal ileum.

 


Figure 24
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Fig. 15B 55-year-old man with obscure gastrointestinal bleeding. Thick-slab volume-rendered image shows vascular structure of distal ileum (arrows) with hypertrophied supplying arteries (arrowheads). There is an early draining vein (not shown). From these confirmatory CT features, mass was diagnosed as arteriovenous malformation of distal ileum.

 
Small-Bowel Neoplasm
Neoplasms of the small bowel are uncommon and are frequently overlooked because of their vague or nonspecific clinical manifestations [19]. Although a fluoroscopic barium study or evolving bowel enteroscopy is usually used to evaluate patients with possible small-bowel neoplasms, CT plays a critical role in the preoperative staging. With the advent of MDCT and the development of 3D image processing, the current role of CT has expanded to the diagnosis and staging of these tumors. When it is difficult to determine their site of origin, 3D imaging may be helpful to better define the site of origin and to help the surgeon plan for resection.

In addition, CT angiography can provide information regarding the vascular supply of the tumor and vascular invasion by the tumor (Figs. 13A and 13B). Therefore, in such patients, administration of a negative oral contrast material (such as water) seems preferable because of its preservation of the vascular information regarding the tumor, the affected bowel segment, and related vascular structures. However, if communication between the necrotic tumor and the adjacent bowel, fistula formation, or perforation is suspected, we prefer the use of a water-soluble positive oral contrast medium.

Obscure Gastrointestinal Bleeding
Compared with the stomach and the colon, the small intestine is an uncommon site for intestinal bleeding, and unless the bleeding is massive, it is often difficult to diagnose. Therefore, such patients may present with prolonged, chronic occult blood loss or recurrent episodes of melena without a specific diagnosis. Although various radiologic studies have been used, a bleeding site cannot be localized in approximately 5-20% of these patients who are therefore classified with obscure gastrointestinal bleeding [20]. Nevertheless, every effort should be made to determine the source of their gastrointestinal bleeding because adequate diagnosis is followed by an improved patient outcome and a decreased need for transfusion.

Although CT is still not comparable in sensitivity to scintigraphy using 99mTc-labeled RBCs or to conventional angiography, it may be an alternative to more invasive procedures when routine workup fails to determine the cause of active intestinal bleeding [21, 22]. With advanced 3D imaging, MDCT (including CT angiography) may have a role in evaluating patients with obscure gastrointestinal bleeding because it can be performed rapidly and noninvasively. Obscure gastrointestinal bleeding, unexpected bleeding foci, unexpected tumors, and inflammatory bowel disease can all be easily observed on MDCT (Figs. 14, 15A, and 15B).


Summary
Top
Abstract
Introduction
MDCT Protocol
Clinical Applications of MDCT
Summary
References
 
MDCT and refined 3D imaging processes can offer a full examination of the small intestine and powerful information about the bowel and its surrounding structures. These are inherent advantages of CT over conventional enteroclysis. In most cases of small-bowel disease, various 3D technologies can help radiologists make an easy, rapid, and accurate diagnosis while avoiding unnecessary examinations. Therefore, knowledge and awareness of the valuable 3D CT features and each proper application technique of MDCT are essential to achieve the diagnostic goal of one-step imaging.


Acknowledgments
 
We thank Bonnie Hami, Department of Radiology, University Hospitals Health System, Cleveland, OH, for editorial assistance in preparing the manuscript.


References
Top
Abstract
Introduction
MDCT Protocol
Clinical Applications of MDCT
Summary
References
 

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