Biomedical subjects

T Q Bartlett

Publications and source records attributed to T Q Bartlett.

4 recordsLinked to original sources

PubMed1998

Reliability of linear alveolar bone loss measurements of mandibular posterior teeth from digitized bitewing radiographs.

Observer reliability in performing linear measurements between the cementoenamel junction and alveolar crest was determined for mandibular posterior teeth from digitized clinical bitewing radiographs acquired during recall examinations. 6 measurements (corresponding to traditional probing measurements) were made per tooth by 3 observers. Mesial and distal measurements made to the most coronal aspects of the alveolar crest were the most reliable and least biased. As was anticipated, intra-observer reliability was better than inter-observer reliability although the 3 observers of our study were able to detect a significant mean change (0.1 mm, p<0.0001) in alveolar bone height over a 1-year period for 10 patients. For our most reliable and unbiased measurements (mesial measurements to the alveolar crest), a change of 0.54 mm (90th percentile) would be required to indicate change at a site from one time to the next. Based on the reliability of our digital radiographic measurements, with the alpha error rate set at 0.05 and beta at 0.20, a difference in alveolar bone height of 0.3 mm could be detected with a patient sample size of between 13 (best case) and 54 (worst case).

Alveolar Bone Loss↗

PubMed1996

Histogram-matching and histogram-flattening contrast correction methods: a comparison.

OBJECTIVES: To compare the results or two methods of histogram matching and two methods of histogram flattening for their ability to correct for contrast variations in digital dental images. METHODS: A custom-built, aluminium stepwedge with 0.1, 0.5 and 1.0 mm steps was placed over Ektaspeed films and exposed for 0.06, 0.12 and 0.25 s, respectively. Radiographs were digitized at 50 microns spatial resolution and 12-bit contrast resolution. Contrast corrections were performed using Rüttimann et al.'s algorithm (1986) for one method of matching (RM) and flattening (RF) and Castleman's algorithm (1979) for the other method of matching (CM) and flattening (CF). Mean pixel grey-scale values were determined for each step. The 0.12 s exposure was considered to be the target image exposure. Absolute differences in pixel grey-scale values between the target images and the modified images were determined. RESULTS: The median values of the absolute differences in pixel grey-scale values between the target images and the contrast corrected images were: CM = 4.3; RM = 4.1; CF = 70.2 and RF = 70.2. CONCLUSION: Castleman's and Rüttimann's matching algorithms perform equally well in correcting digital image contrast. Histogram flattening was less effective.

Algorithms↗

PubMed1994

Bitewing-based alveolar bone densitometry: digital imaging resolution requirements.

The resolution requirements were determined for detection of incremental alveolar bone loss from digitized Ektaspeed radiographs. Ten clinical radiographs were examined with a calibrated optical microscope to measure the smallest feature of interest discernible for alveolar bone. Images of trabeculae > 100 microns in diameter could be identified, but smaller ones could not be resolved. The Nyquist Criterion requires sampling with 50 microns (or smaller) pixels to measure such features. Numerous 25 microns Ag aggregates were present. Fifty microns resolution is a practical compromise between noise level and feature resolution. In another example of 10 bitewings digitized at 8 bit grey scale, about half the available range was used for alveolar bone, resulting in uncertainty, over a range of 2 optical density (OD) units, of about 1.42% at the average OD for alveolar bone (1.1). With the same radiographs digitized at 12 bit resolution, over 2000 of 4096 grey scales were used with a corresponding uncertainty of about 0.09%. Twelve-bit precision was also able to resolve smaller increments in an aluminium stepwedge than was 8 bit precision. Twelve-bit grey scale and 50 microns spatial resolution are recommended for alveolar bone densitometry performed with Ektaspeed radiographs.

Absorptiometry, Photon↗

PubMedDate not supplied

Interactive segmentation of cerebral gray matter, white matter, and CSF: photographic and MR images.

Digital photography of postmortem brain slices was compared with magnetic resonance imaging (MRI) for morphological analysis of human brain atrophy. In this study, we used two human brains obtained at autopsy: a cognitively defined nondemented control (70-yr-old male) and a demented Alzheimer's disease (AD) subject (82-yr-old female). For each of two brains, interactive manual image segmentation was performed by two observers on two image sets: (a) four coronal T1-weighted MR images (5 mm slices); and (b) four digitized photographic images from comparable rostrocaudal levels. Microcomputer image analysis software was used to measure the areas of three segmented cerebral compartments--gray matter (GM), white matter (WM) and CSF--for both image types. Resegmentation error was defined as the absolute difference between the areas derived from two segmentation trials divided by the value from trial 1 and multiplied by 100. This yielded the percent difference between the area measurements from the two trials. We found intra-observer agreement was better (error rates 1-18%) than inter-observer agreement (3-70%) with best agreement for WM and least for CSF, the smallest object class. MRI overestimated GM area relative to digitized photographs in the control but not the AD brain. The results define limitations of manual image segmentations and comparison of MRI with pathologic section photographic images.

Aged↗