Comparison of Single‐slice Computed Tomography Protocols for Detection of Pulmonary Nodules in Dogs

Abstract

Two dogs (4 and 38 kg) with radiographic evidence of pulmonary nodules were evaluated using single-slice, helical computed tomography (CT). Each thorax was scanned using 12 combinations of examination parameters that included slice collimation width (3 and 5mm for the small dog and 5 and 7mm for the large dog), pitch (1, 1.5, and 2), and reconstruction interval (0.5 and 1). Sensitivity, specificity, and accuracy for nodule detection were evaluated for each protocol by three different observers, their results being compared with a consensus evaluation of images acquired with the protocol providing the best theoretic resolution (narrow collimation, pitch of 1, reconstruction interval of 0.5). For all observers, sensitivity and accuracy were significantly increased when using a protocol with narrow collimation (P < 0.0001-0.005 and P = 0.0003-0.005, respectively). Pitch and reconstruction interval did not significantly influence the accuracy, sensitivity, or specificity for at least two of the observers. Additionally, nodule size (< 3mm vs. > 3mm) did not significantly affect nodule detection. Interobserver repeatability was variable among protocols (K = 0.32-0.78), highlighting the fact that nodule detection may be more dependent on the observer than on the choice of the CT protocol. For single-slice CT, the results of this study suggest that narrow collimation (3-5 mm, depending on the animal's size), a pitch of 2 and a reconstruction interval of 1 should be used in dogs for the detection of pulmonary nodules.

A Comparison of Computed Tomography, Computed Radiography, and Film‐screen Radiography for the Detection of Canine Pulmonary Nodules

“…Another contributing explanation is that the comparison standard comes from a consensus reading, selected to avoid the pitfalls in a single observer's reliability. There exists individual variation in determination of positive or negative status and even larger variation in identification of individual pulmonary nodules . Thus, an appropriately structured multiple‐reader consensus is used in many clinical studies to obtain a true diagnosis .…”

“…This has several unfortunate implications. First, when only CT examination is available, atelectasis in this region can potentially cause an interpretation error . Second, when recommending CT examination for confirmation of a radiographically suspected pulmonary nodule in this area, the potential of atelectasis masking the nodule should be considered.…”

“…CT consisted of a noncontrast enhanced helical scan performed under general anesthesia with positive‐pressure (15 mmHg) breath‐hold using a third‐generation single‐slice CT scanner (HiSpeed ZXi, )§. Slice thickness was 3 (small dogs) or 5 mm (medium‐sized and large dogs) with either a 0.5:1 or 1:1 reconstruction interval and pitch was 1:1 . Image matrix was 512 × 512 and display field of view varied with patient size.…”

Computed Tomography Characteristics of Canine Tracheobronchial Lymph Node Metastasis

“…Respiratory motion also caused difficulty in interpretation and reconstruction of images, which can easily be remedied in future studies with either breath holding techniques 33 or hyperventilation‐induced brief apnea while scanning a series of thin slices through the area of the tracheal bifurcation. Multislice detector units may minimize the need for breath control.…”

THE VETMOUSETRAP™: A DEVICE FOR COMPUTED TOMOGRAPHIC IMAGING OF THE THORAX OF AWAKE CATS

“…The selection of pitch is a trade‐off between patient coverage and accuracy. Larger pitches reduce scanning time, allowing more coverage of a patient per unit of time, but slice data must be interpolated using scan data that is farther from the actual slice, producing more artifacts 31,32 . In pediatric thoracic CT, although no single helical CT technique has gained universal acceptance, in general, a pitch of at least 1.3 is used and several authors use a pitch from 1.3 to 1.6 16 .…”