Summation or Axial Slab Average Intensity Projection of Abdominal Thin-section CT Datasets: Can They Substitute for the Primary Reconstruction from Raw Projection Data?

Abstract

We hypothesized that that the summation or axial slab average intensity projection (AIP) techniques can substitute for the primary reconstruction (PR) from a raw projection data for abdominal applications. To compare with PR datasets (5-mm thick, 20% overlap) in 150 abdominal studies, corresponding summation and AIP datasets were calculated from 2-mm thick images (50% overlap). The root-mean-square error between PR and summation images was significantly greater than that between PR and AIP images (9.55 [median] vs. 7.12, pG0.0001, Wilcoxon signed-ranks test). Four radiologists independently compared 2,000 test images (PR [as control], summation, or AIP) and their corresponding PR images to prove that the identicalness of summation or AIP images to PR images was not 1% less than the assessed identicalness of PR images to themselves (Wald-type test for clustered matched-pair data in a non-inferiority design). For each reader, both summation and AIP images were not inferior to PR images in terms of being rated identical to PR (p G0.05). Although summation and AIP techniques produce images that differ from PR images, these differences are not easily perceived by radiologists. Thus, the summation or AIP techniques can substitute for PR for the primary interpretation of abdominal CT.

Detection of the Normal Appendix with Low-Dose Unenhanced CT: Use of the Sliding Slab Averaging Technique

“…As the slab moves along the viewing direction in small increments, overlapping slabs are rapidly rendered in a real-time manner, creating an illusion of image-to-image continuity. By virtue of the reduction of image noise and the preservation of spatial resolution inherent in the source thin-section images (9,10), the sliding slab averaging technique can enhance the differentiation of a small target, such as the appendix, from the surrounding structures, such as the vessels or bowel loops. In a prior study (5), we compared the sliding slab averaging mode with the conventional stack mode in the review of scans obtained with a higher radiation dose and intravenous contrast material enhancement, and we found that use of the sliding slab averaging technique improved appendiceal visualization.…”

“…While there has been considerable debate on the need for intravenous or enteric contrast material enhancement, to our knowledge, few studies have been focused on techniques for image reconstruction (17) or review (4,5); these techniques are also important in the visualization of the normal or inflamed appendix. The sliding slab averaging mode operates by rendering, within the acquired volume data, only those areas that lie between a set of parallel clipping planes oriented perpendicular to the chosen viewing direction (10,31). Averaging pixel values within the slab along the viewing direction (a 5-mm slab thickness was the default setting in our study) usually leads to an improvement in the quality of the displayed image as compared with that of noisy thin-section source images (0.67-mm slab thickness for images acquired with the 64 -detector row scanner) because the noise is reduced across the thin-section images being averaged.…”

“…The sliding slab averaging technique is a real-time image postprocessing technique that is available on most commercial CT workstations and can enhance depiction of the normal or diseased appendix (5,6) with use of the following features to take full advantage of the performance of the modern scanner (7)(8)(9)(10). First, by interactively adjusting the slab thickness according to the target lesion size, the trade-off between through-plane resolution and image noise can be adapted.…”

Patency of splenic vessels after laparoscopic spleen and splenic vessel-preserving distal pancreatectomy

“…The scans were reviewed using an interactive sliding slab ray sum technique (AquariusNET; TeraRecon, San Mateo, California, USA) with a maximum slab thickness of 3 mm. This reviewing technique 16 is available in many commercial CT workstations, and accurately depicts pathology in small tubular structures such as vessels 17,18 . To evaluate vascular patency, the radiologists used appropriate magnification, and changed the viewing plane such that it was parallel or perpendicular to the target segment of vessel being analysed.…”

Informatics in Radiology: Sliding-Thin-Slab Averaging for Improved Depiction of Low-Contrast Lesions with Radiation Dose Savings at Thin-Section CT

“…Previous studies were focused mainly on the use of this technique to obtain maximum or minimum intensity projections for pulmonary evaluations (29,30). Lee et al, in two separate studies (31,32), showed that the sliding-thin-slab display mode enhances reader confidence when compared with the stack mode in the diagnosis of acute appendicitis (31) and that the summation of thin sections is equivalent to the primary reconstruction of thicker sections (32). More recently, it was demonstrated that the optimal slab thickness depends on the size of the lesion to be detected and that the slab thickness should be interactively varied during the reading process at the workstation (11) (Movie 2 [online]).…”