Biomedical subjects

Raleigh F Johnson

Publications and source records attributed to Raleigh F Johnson.

4 recordsLinked to original sources

PubMed2005

Thickness of molybdenum filter and squared contrast-to-noise ratio per dose for digital mammography.

OBJECTIVE: The objective of our study was to test whether the lesion-tissue contrast-to-noise ratio (CNR) at a given dose level can be improved by increasing the thickness of the molybdenum (Mo) filter currently used in digital mammography. MATERIALS AND METHODS: We studied how the CNR between breast and a 5-mm simulated infiltrating ductal carcinoma (IDC) embedded in a 5-cm-thick breast changes with Mo filter thickness. We performed phantom imaging experiments by modifying the filter wheel of a Senographe 2000D unit with Mo filters that ranged from 15 to 90 microm in thickness. A 5-cm-thick 50% glandular-50% adipose breast phantom with a 5-mm insert simulating IDC was used as the phantom for all the cases. The CNRs between the breast phantom and the IDC insert were measured, and average glandular doses were calculated using a filtration-dependent X-ray spectra model and a breast dosimetry model based on a validated Monte Carlo simulation. RESULTS: The lesion-tissue CNR at a given dose level increases with increasing Mo filter thickness from 15 to 90 microm. The measured squared CNR per dose increased by 8%, 14%, 17%, and 17% for 45-, 60-, 75-, and 90-microm Mo filters, respectively, compared with the standard 30-microm Mo filter. Meanwhile, the exposure times were increased by 35% (45 microm), 71% (60 microm), 177% (75 microm), and 229% (90 microm). CONCLUSION: Increasing Mo filter thickness from 30 to 60 microm can increase lesion-tissue squared CNR per dose by 14% with a tolerable increase in the duration of exposure.

Breast Neoplasms↗

PubMed2003

Aeration following intact canal wall mastoidectomy.

This study examines the prevalence and extent of re-aeration of the mastoid cavity following intact canal wall (ICW) mastoidectomy. Temporal bone computed tomography scans from patients with prior unilateral ICW mastoidectomy were identified. Three-dimensional volume reconstruction of the temporal bone was performed to measure aeration bilaterally. Thirty-five scans were analyzed; 16 (46%) showed good aeration in the operated ear and 19 showed poor aeration. The aeration (volume) in the surgical ears and the contralateral ears was significantly less than that in subjects without a history of ear disease. Those with poor aeration were more likely to require additional surgery. For temporal bone pairs with greater volume in the operated ear, the average difference was 1.3 cm3. Surgical creation of a mastoid cavity does not produce a large increase in aeration as compared with the contralateral ear. Following surgery, mastoid opacification may presage recurrent disease. Routine use of mastoidectomy in an attempt to improve aeration is not advocated.

Adolescent↗

PubMed2002

Evaluation of the internal auditory canal with virtual endoscopy.

OBJECTIVE: Three-dimensional imaging can improve the understanding and comprehension of complex anatomy. Recent advances in software development allow the construction of a virtual endoscopic view of anatomic structures. This report applies virtual endoscopic capabilities to imaging of the internal auditory canal. STUDY DESIGN, SETTING, AND PATIENTS: We conducted a retrospective case review at a tertiary referral center of patients with abnormal internal auditory canal anatomy on computed tomography. INTERVENTIONS: Computed tomography images were obtained using conventional clinical algorithms involving multiple, 1-mm-thick slices through the temporal bone. Three-dimensional reconstructions were made using General Electric Advantage Windows Navigator software. The virtual endoscopic image-processing algorithm used selected image intensity threshold levels to visualize internal auditory canal anatomy from an endoscopic perspective. RESULTS: Eleven cases of abnormalities of the internal auditory canal were retrospectively identified. Clinical applications using the virtual endoscopic images are presented. The virtual endoscopic images supported prior clinical decision making in 6 of the 11 cases evaluated. CONCLUSION: This technique shows promise for the diagnosis, surgical planning, and teaching of temporal bone anatomy. Usefulness is dependent on acquisition parameters and clinical indications for examination.

Algorithms↗

PubMed2002

3D CT imaging method for measuring temporal bone aeration.

OBJECTIVE: 3D volume reconstruction of CT images can be used to measure temporal bone aeration. This study evaluates the technique with respect to reproducibility and acquisition parameters. MATERIAL AND METHODS: Helical CT images acquired from patients with radiographically normal temporal bones using standard clinical protocols were retrospectively analyzed. 3D image reconstruction was performed to measure the volume of air within the temporal bone. The appropriate threshold values for air were determined from reconstruction of a phantom with a known air volume imaged using the same clinical protocols. The appropriate air threshold values were applied to the clinical material. RESULTS: Air volume was measured according to an acquisition algorithm. The average volume in the temporal bone CT group was 5.56 ml, compared to 5.19 ml in the head CT group (p = 0.59). The correlation coefficient between examiners was > 0.92. There was a wide range of aeration volumes among individual ears (0.76-18.84 ml); however, paired temporal bones differed by an average of just 1.11 ml. CONCLUSIONS: The method of volume measurement from 3D reconstruction reported here is widely available, easy to perform and produces consistent results among examiners. Application of the technique to archival CT data is possible using corrections for air segmentation thresholds according to acquisition parameters.

Adult↗