Cynthia Elizabeth Landberg Davis

Dual-Energy X-Ray Absorptiometry for Quantification of Visceral Fat

Obesity is the major risk factor for metabolic syndrome and through it diabetes as well as cardiovascular disease. Visceral fat (VF) rather than subcutaneous fat (SF) is the major predictor of adverse events. Currently, the reference standard for measuring VF is abdominal X‐ray computed tomography (CT) or magnetic resonance imaging (MRI), requiring highly used clinical equipment. Dual‐energy X‐ray absorptiometry (DXA) can accurately measure body composition with high‐precision, low X‐ray exposure, and short‐scanning time. The purpose of this study was to validate a new fully automated method whereby abdominal VF can be measured by DXA. Furthermore, we explored the association between DXA‐derived abdominal VF and several other indices for obesity: BMI, waist circumference, waist‐to‐hip ratio, and DXA‐derived total abdominal fat (AF), and SF. We studied 124 adult men and women, aged 18–90 years, representing a wide range of BMI values (18.5–40 kg/m2) measured with both DXA and CT in a fasting state within a one hour interval. The coefficient of determination (r2) for regression of CT on DXA values was 0.959 for females, 0.949 for males, and 0.957 combined. The 95% confidence interval for r was 0.968 to 0.985 for the combined data. The 95% confidence interval for the mean of the differences between CT and DXA VF volume was −96.0 to −16.3 cm3. Bland‐Altman bias was +67 cm3 for females and +43 cm3 for males. The 95% limits of agreement were −339 to +472 cm3 for females and −379 to +465 cm3 for males. Combined, the bias was +56 cm3 with 95% limits of agreement of −355 to +468 cm3. The correlations between DXA‐derived VF and BMI, waist circumference, waist‐to‐hip ratio, and DXA‐derived AF and SF ranged from poor to modest. We conclude that DXA can measure abdominal VF precisely in both men and women. This simple noninvasive method with virtually no radiation can therefore be used to measure VF in individual patients and help define diabetes and cardiovascular risk.

Fat‐referenced MR thermometry in the breast and prostate using IDEAL

To demonstrate a three‐echo fat‐referenced MR thermometry technique that estimates and corrects for time‐varying phase disturbances in heterogeneous tissues.

Relationship between dual-energy X-ray absorptiometry volumetric assessment and X-ray computed tomography-derived single-slice measurement of visceral fat

To reduce radiation exposure and cost, visceral adipose tissue (VAT) measurement on X-ray computed tomography (CT) has been limited to a single slice. Recently, the US Food and Drug Administration has approved a dual-energy X-ray absorptiometry (DXA) application validated against CT to measure VAT volume. The purpose of this study was to develop an algorithm to compute single-slice area values on DXA at 2 common landmarks, L2/3 and L4/5, from an automated volumetrically derived measurement of VAT. Volumetric CT and total body DXA were measured in 55 males (age: 21-77 yr; body mass index [BMI]: 21.1-37.9) and 60 females (age: 21-85 yr; BMI: 20.0-39.7). Equations were developed by applying the relationship of CT single-slice area and volume measurements of VAT to the DXA VAT volume measure as well as validating these against the CT single-slice measurements. Correlation coefficients between DXA estimate of single-slice area and CT were 0.94 for L2/3 and 0.96 for L4/5. The mean difference between DXA estimate of single-slice area and CT was 5 cm(2) at L2/3 and 3.8 cm(2) at L4/5. Bland-Altman analysis showed a fairly constant difference across the single-slice range in this study, and the 95% limits of agreement for the 2 methods were -44.6 to +54.6 cm(2) for L2/3 and -47.3 to +54.9 cm(2) for L4/5. In conclusion, a volumetric measurement of VAT by DXA can be used to estimate single-slice measurements at the L2/3 and the L4/5 landmarks.

Rapid HIFU autofocusing using the entire MR-ARFI image

Phase aberrations and attenuations caused by bone can defocus HIFU in the brain and organs behind the ribcage. To refocus the beam, MR-ARFI can be used to measure tissue displacements created by each element in the transducer, and optimize driving signal delays and amplitudes. We introduce a new MR-ARFI-based autofocusing method that requires many fewer image acquisitions than current methods. The method is validated in simulations of bone and brain HIFU transducers, and compared to a conventional method.

Preliminary Clinical Experience with a Combined Automated Breast Ultrasound and Digital Breast Tomosynthesis System

We analyzed the performance of a mammographically configured, automated breast ultrasound (McABUS) scanner combined with a digital breast tomosynthesis (DBT) system. The GE Invenia ultrasound system was modified for integration with GE DBT systems. Ultrasound and DBT imaging were performed in the same mammographic compression. Our small preliminary study included 13 cases, six of whom had contained invasive cancers. From analysis of these cases, current limitations and corresponding potential improvements of the system were determined. A registration analysis was performed to compare the ease of McABUS to DBT registration for this system with that of two systems designed previously. It was observed that in comparison to data from an earlier study, the McABUS-to-DBT registration alignment errors for both this system and a previously built combined system were smaller than those for a previously built standalone McABUS system.

Image registration for microwave tomography of the breast using priors from non-simultaneous previous magnetic resonance images

Microwave tomography (MT), a novel imaging modality in which the body is probed non-invasively using non-ionizing high-frequency radio-frequency waves, has shown promise for breast cancer screening and more recently for the monitoring of chemotherapy treatment. As an inherently low-resolution modality, it has been shown that prior structural information from another imaging modality, such as magnetic resonance imaging (MRI), can be used to improve the spatial resolution and quantitative accuracy of MT. In this paper, we show the results of a single-patient trial in which we co-register a non-simultaneous prior MRI with MT data acquired in a fluid bath. For the purposes of registration evaluation, two MRI images were acquired, one in air and one in fluid, and the registration errors were evaluated for manually selected internal image features, for a number of image registration algorithms.