Usefulness and limitations of dual-layer spectral detector computed tomography for diagnosing biliary stones not detected by conventional computed tomography: a report of three cases

Principles and Applications of Dual-Layer Spectral CT in Gastrointestinal Imaging

The advance in technology allows for the development of different CT scanners in the field of dual-energy computed tomography (DECT). In particular, a recently developed detector-based technology can collect data from different energy levels, thanks to its layers. The use of this system is suited for material decomposition with perfect spatial and temporal registration. Thanks to post-processing techniques, these scanners can generate conventional, material decomposition (including virtual non-contrast (VNC), iodine maps, Z-effective imaging, and uric acid pair images) and virtual monoenergetic images (VMIs). In recent years, different studies have been published regarding the use of DECT in clinical practice. On these bases, considering that different papers have been published using the DECT technology, a review regarding its clinical application can be useful. We focused on the usefulness of DECT technology in gastrointestinal imaging, where DECT plays an important role.

Dual-layer spectral detector computed tomography versus magnetic resonance cholangiopancreatography for biliary stones

OBJECTIVE

Dual-layer spectral detector computed tomography (DLCT) can detect noncalcified biliary stones. The diagnostic ability of DLCT for detecting biliary stones may be comparable to that of magnetic resonance cholangiopancreatography (MRCP). This study seeks to compare the diagnostic ability for biliary stones between these two imaging modalities.

METHODS

This retrospective study included 102 cases with a diagnosis of biliary stones including gallstones (n = 66) and common bile duct (CBD) stones (n = 25) or spontaneously passing CBD stones (n = 11). The reference standard used was operative findings, endoscopic retrograde cholangiopancreatography or follow-up over 6 months. In DLCT, 120-kVp images, 40-keV virtual monoenergetic images and material decomposition images were created. We compared the diagnostic ability of DLCT and MRCP for biliary stones using the McNemar's test.

RESULTS

The sensitivity and specificity of DLCT versus MRCP for biliary stones were 91.2% versus 95.6% and 90.9% versus 90.9%. Thus, the sensitivity and specificity were not significantly different (P = 0.25 and P = 1.0). Although in small stones (<9 mm) the sensitivity of calcified stones was not different between DLCT and MRCP (100% versus 92.5%), the sensitivity of noncalcified stones in DLCT was lower than that in MRCP (38.5% versus 100%).

CONCLUSION

The diagnostic ability of biliary stones in DLCT appears comparable to that of MRCP in overall cases. However, detecting noncalcified stones less than 9 mm in size is limited in DLCT.

Post-endoscopic retrograde cholangiopancreatography pancreatitis in patients with asymptomatic common bile duct stones

BACKGROUND AND AIM

For asymptomatic common bile duct (CBD) stones, removal by endoscopic retrograde cholangiopancreatography (ERCP) is recommended in available guidelines. However, few studies have reported the risk of post-ERCP pancreatitis (PEP), which is the most common and serious ERCP-related complication for asymptomatic CBD stones. We performed a propensity score matching analysis to examine the risk of PEP in therapeutic ERCP for asymptomatic CBD stones.

METHODS

Information from medical databases of three institutions in Japan was collected over 6 years to identify 1113 patients with native papilla who underwent therapeutic ERCP for choledocholithiasis (excluding biliary pancreatitis). We compared the risk of PEP between asymptomatic and symptomatic groups by performing one-to-one propensity score matching.

RESULTS

PEP was present in 52 (4.7%) of the 1113 patients overall. Of the 949 symptomatic patients, 28 (3.0%) had PEP, and of the 164 asymptomatic patients, 24 (14.6%) had PEP. The incidence of PEP was significantly higher in the asymptomatic group than in the symptomatic group (3.0% vs 14.6%; P < 0.001, odds ratio = 5.6). Of the 158 propensity score-matched symptomatic patients, five (3.2%) had PEP. In contrast, of the 158 propensity score-matched asymptomatic patients, 24 (15.2%) had PEP. Propensity score matching analysis revealed that the risk of PEP increased significantly in the asymptomatic group compared with the symptomatic group (3.2% vs 15.2%; P < 0.001, odds ratio = 5.5).

CONCLUSIONS

ERCP for asymptomatic CBD stones had a high risk of PEP. Endoscopists should explain in detail the risk of PEP to patients, especially those with asymptomatic CBD stones.

Evaluation of lung transplant perfusion using iodine maps from novel spectral detector computed tomography

We report the case of a 51-year-old patient who underwent bilateral lung transplantation and presented with an unstable condition and sepsis 6 days after transplantation. The performed contrast enhanced spectral detector computed tomography (CT) using a dual-layer detector showed absence of perfusion in the left lung on iodine maps, although branches of the pulmonary artery were patent. This prompted retrospective evaluation of CT images and total venous occlusion of the left pulmonary veins was found. Here, iodine maps helped in raising conspicuity of loss of lung perfusion.

Reduced iodinated contrast media for abdominal imaging by dual-layer spectral detector computed tomography for patients with kidney disease

Contrast-enhanced computed tomography using iodinated contrast media is useful for diagnosis of gastrointestinal diseases. However, contrast-induced nephropathy remains problematic for kidney diseases patients. Although current guidelines recommended the use of a minimal dose of contrast media necessary to obtain adequate images for diagnosis, obtaining adequate images with sufficient contrast enhancement is difficult with conventional computed tomography using reduced contrast media. Dual-layer spectral detector computed tomography enables the simultaneous acquisition of low- and high-energy data and the reconstruction of virtual monochromatic images ranging from 40 to 200 keV, retrospectively. Low-energy virtual monochromatic images can enhance the contrast of images, thereby facilitating reduced contrast media. In case 1, abdominal computed tomography angiography at 50 keV using 40% of the conventional dose of contrast media revealed the artery that was the source of diverticular bleeding in the ascending colon. In case 2, ischemia of the transverse colon was diagnosed by contrast-enhanced computed tomography and iodine-selective imaging using 40% of the conventional dose of contrast media. In case 3, advanced esophagogastric junctional cancer was staged and preoperative abdominal computed tomography angiography could be obtained with 30% of the conventional dose of contrast media. However, the texture of virtual monochromatic images may be a limitation at low energy.