Comparison of Transverse Computed Tomographic Excretory Urography Images and Maximum Intensity Projection Images for Diagnosing Ectopic Ureters in Dogs

Abstract

Computed tomographic maximum intensity projection (MIP) images have been shown to improve reader confidence in their diagnoses and to improve detection of vascular structures and pulmonary nodules. The objectives of this method comparison study were to compare transverse source computed tomographic excretory urography (CTEU) images to two, five, and 10 slab thick MIP images for diagnosing canine ectopic ureters, compare reader confidence, and evaluate interobserver agreement. Two board-certified veterinary radiologists and a board-certified small animal internist blindly reviewed transverse source CTEU and two, five, and 10 slab thick MIP images of 24 dogs enrolled in the study. Inclusion criteria included a diagnostic CTEU and either cystoscopic or surgical confirmation of the presence or absence of ureteral ectopia. Eleven dogs were confirmed to have 17 ectopic ureters at surgery and/or cystoscopically. There was no significant difference in reader diagnoses between viewing methods or between viewing methods and the surgical/cystoscopic findings (P < 0.001). Reader confidence was significantly greater on two (P = 0.0080) and five (P = 0.0009) slab thick MIP images with significant interobserver agreement between readers for all viewing methods (P values ranging between 0.0363 and <0.001). In addition, the diagnostic accuracy of MIP images was similar to or better than transverse source CTEU images, when assessed by a radiologist. The study results suggest that CTEU is a reliable imaging technique for diagnosing canine ectopic ureters among specialists of varied experience. In addition, thin slice reconstructed MIP images improve reader confidence and potentially diagnostic accuracy, and thus their use should be considered, especially in more challenging cases.

Four‐dimensional CT excretory urography is an accurate technique for diagnosis of canine ureteral ectopia

“…All examinations were randomized and pseudonymized in a spreadsheet file and a scoring exercise performed at least 1 month after the clinical examination of the cases and performed separately for the CTEU and 4D‐CTEU examinations. To score ureteral topia on both CTEU and 4D‐CTEU, a modified grading system was used independently by two different observers with different levels of experience (ML, a third‐year resident in veterinary diagnostic imaging, and TS, a board‐certified veterinary radiologist): 0, definitely normotopic ureter; 1, probably normotopic ureter; 2, equivocal ureteral topia; 3, probably ectopic ureter; 4, definitively ectopic ureter 14 . Both observers were unaware of the confirmation of diagnosis results at the time of scoring.…”

“…Moreover, murality of the ectopic ureters was scored by the same observers by consensus (ML and TS) during the second session as follows: 0, definitely extramural bridging (coursing extramurally); 1, probably extramural bridging; 2, equivocally intra/extramural; 3, probably intramural tunneling; 4, definitely intramural tunneling; 5, normal exam; 6, nondiagnostic exam for tunneling/bridging determination. If needed, multiplanar maximum intensity projections were used by the reviewers in a combined session with slab thickness of 2‐5 mm as previously reported 13,14 . In all ureters, the UVJ angle was measured on the 4D‐CTEU study on multiplanar reconstructed images at a temporal window displaying the ureter contrast bolus, using the angle tool of the DICOM viewer software by a single author who was experienced in the imaging anatomy and the DICOM viewer software (ML).…”

“…Computed tomographic excretory urography in dogs was established two decades ago 11 and promoted more than a decade ago as the modality of choice for canine UE workup 9 . However, only recent investigations focused on the technical improvement of this modality in order to increase readers’ confidence and diagnostic accuracy 12–14 . Most of these recent advances describe the use of postprocessing techniques such as the application of maximum intensity projection to highlight the pathways of the ureters or else they focus on the description of common features of ureteral ectopia (UE) seen in CT 14–16 .…”

“…However, only recent investigations focused on the technical improvement of this modality in order to increase readers’ confidence and diagnostic accuracy 12–14 . Most of these recent advances describe the use of postprocessing techniques such as the application of maximum intensity projection to highlight the pathways of the ureters or else they focus on the description of common features of ureteral ectopia (UE) seen in CT 14–16 . No substantial changes in the acquisition process of the CT images have been proposed other than using bolus tracking techniques or furosemide administration to increase ureteral visibility 13,14 .…”

“…Most of these recent advances describe the use of postprocessing techniques such as the application of maximum intensity projection to highlight the pathways of the ureters or else they focus on the description of common features of ureteral ectopia (UE) seen in CT 14–16 . No substantial changes in the acquisition process of the CT images have been proposed other than using bolus tracking techniques or furosemide administration to increase ureteral visibility 13,14 . Four‐dimensional CT is a new image acquisition technique available in the latest generation of multi‐slice CT scanners, in which a patient area is scanned with a continuous series of helical scans in back and forward directions.…”