Biomedical subjects

Kristina T Johnson

Publications and source records attributed to Kristina T Johnson.

4 recordsLinked to original sources

PubMed2007

Development of a cathartic-free colorectal cancer screening test using virtual colonoscopy: a feasibility study.

OBJECTIVE: The purpose of our study was to develop a method to subtract barium-labeled stool from the colon using a phantom and to evaluate the performance of the technique in a pilot human population. MATERIALS AND METHODS: A phantom containing 6-mm flat polyps and three types of simulated stool (homogeneous, moderately heterogeneous, and severely heterogeneous) mixed with barium was created, scanned, and tested using three stool subtraction algorithms but no cathartic. Thirty patients with suspected colorectal polyps were studied using stool tagging to determine which was the most effective stool subtraction algorithm. Colonoscopy was the reference standard. Examinations were evaluated blindly using the unsubtracted and 6 weeks later both the unsubtracted and subtracted data sets. RESULTS: A threshold of 200 H and expansion and convolution techniques were the most effective tools for subtracting stool and minimizing artifacts. When applied to the human population, sensitivities using the unsubtracted data sets were 90% (18/20) and 68% (26/38) for polyps > or = 1 cm and > or = 5 mm, respectively. Specificities were 100% (4/4) and 75% (3/4) for polyps > or = 1 cm and > or = 5 mm. For the stool-subtracted data sets, sensitivities were 90% (18/20) and 71% (27/38) for polyps > or = 1 cm and > or = 5 mm. Per patient sensitivities were 88% (15/17) and 77% (20/26) for > or = 1 cm and > or = 5 mm polyps. Specificities were 100% (4/4) for large polyps and 25% (1/4) for smaller polyps. CONCLUSION: Image processing tools combining thresholding, expansion, and convolution were the most useful for stool subtraction. Laxative-free colon examinations using barium for stool labeling can be performed at CT colonography with or without stool subtraction with high accuracy. Further study is warranted.

Algorithms↗

PubMed2007

Polyp measurement with CT colonography: multiple-reader, multiple-workstation comparison.

OBJECTIVE: The risk of invasive colorectal cancer in colorectal polyps correlates with lesion size. Our purpose was to define the most accurate methods for measuring polyp size at CT colonography (CTC) using three models of workstations and multiple observers. MATERIALS AND METHODS: Six reviewers measured 24 unique polyps of known size (5, 7, 10, and 12 mm), shape (sessile, flat, and pedunculated), and location (straight or curved bowel segment) using CTC data sets obtained at two doses (5 mAs and 65 mAs) and a previously described colonic phantom model. Reviewers measured the largest diameter of polyps on three proprietary workstations. Each polyp was measured with lung and soft-tissue windows on axial, 2D multiplanar reconstruction (MPR), and 3D images. RESULTS: There were significant differences among measurements obtained at various settings within each workstation (p < 0.0001). Measurements on 2D images were more accurate with lung window than with soft-tissue window settings (p < 0.0001). For the 65-mAs data set, the most accurate measurements were obtained in analysis of axial images with lung window, 2D MPR images with lung window, and 3D tissue cube images for Wizard, Advantage, and Vitrea workstations, respectively, without significant differences in accuracy among techniques (0.11 < p < 0.59). The mean absolute error values for these optimal settings were 0.48 mm, 0.61 mm, and 0.76 mm, respectively, for the three workstations. Within the ultralow-dose 5-mAs data set the best methods for Wizard, Advantage, and Vitrea were axial with lung window, 2D MPR with lung window, and 2D MPR with lung window, respectively. Use of nearly all measurement methods, except for the Vitrea 3D tissue cube and the Wizard 2D MPR with lung window, resulted in undermeasurement of the true size of the polyps. CONCLUSION: Use of CTC computer workstations facilitates accurate polyp measurement. For routine CTC examinations, polyps should be measured with lung window settings on 2D axial or MPR images (Wizard and Advantage) or 3D images (Vitrea). When these optimal methods are used, these three commercial workstations do not differ significantly in acquisition of accurate polyp measurements at routine dose settings.

Algorithms↗

PubMed2006

Visceral fat analysis at CT colonography.

RATIONALE AND OBJECTIVES: Obesity is associated with increased risks for colorectal neoplasia. Few studies have examined quantitative body fat measurements as predictors of colorectal polyps. The objective is to determine whether visceral fat is associated with colorectal polyps at computed tomography (CT) colonography. MATERIALS AND METHODS: Case (n = 25) and control (n = 25) subjects with proven large (>1 cm) colorectal adenomas or normal colons respectively were randomly selected from among an established CT colonography research study cohort. Using supine CT colonography data, the body wall was traced at three levels: top of the right kidney, iliac crest, and superior acetabulum. Total area from the three slices and each slice area were determined within the visceral fat range (-170 to -45 Hounsfield units) and recorded within the selected region. Visceral fat measures were compared between patient groups with and without polyps. RESULTS: None of the single slice visceral fat area measures or summed measures predicted case or control status. The most informative visceral fat measure was obtained at the top of the right kidney with a maximum area under the received operator characteristic curve of 0.77 (0.05 SE). For a selected sensitivity of 75%, the maximum specificity for a large (>or=1 cm) polyp was 64%. CONCLUSION: In this pilot study, visceral fat measures at CT colonography were not significantly associated with the presence of large colorectal adenomas. However, odd ratios were elevated by a factor of 2. This suggests that a larger study may be justified.

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PubMed2006

CT colonography using 360-degree virtual dissection: a feasibility study.

OBJECTIVE: Using a 3D rendering technique called "virtual dissection," we sought to evaluate polyp and fold distortion using a colon phantom, estimate the polyp detection performance in humans, and estimate the added benefit of double interpretation and computer-aided diagnosis. MATERIALS AND METHODS: A colon phantom containing 144 polyps of varying sizes (5-12 mm) and shapes (flat, sessile, pedunculated) was scanned. Polyp shape and distortion at virtual dissection were categorized as flame, club, pea, or bizarre. Haustral fold distortion was graded. The CT colonography examinations in 20 consecutive patients (colonoscopically proven normal findings, n = 5; polyps > or = 1 cm, n = 17 in 15 patients) were blindly reviewed by three radiologists using the virtual dissection technique. The added benefits of double interpretation and computer-aided diagnosis were tabulated. RESULTS: Sessile polyps appeared flame (35/48 [73%]) or pea (11/48 [23%]) in shape. Flat polyps appeared flame-shaped (31/47 [66%]) or pea-shaped (16/47 [34%]). Pedunculated polyps were flame (15/45 [33%]), club (20/45 [44%]), or pea (6/45 [13%]) in shape. Axial distortion occurred along the longitudinal axis. The sensitivities of the three observers for polyps of 1 cm or more were 16/17 (94%), 14/17 (82%), and 15/17 (88%). The specificities were 5/5 (100%), 5/5 (100%), and 4/5 (80%). Sensitivities after double interpretation and computer-aided diagnosis improved but did not reach statistical significance. CONCLUSION: Although distortion of colonic structures exists at virtual dissection, it does so in recognizable patterns, so that sensitivity for polyp detection is not compromised.

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