Biomedical subjects

R Choe

Publications and source records attributed to R Choe.

5 recordsLinked to original sources

PubMed2003

Three-dimensional diffuse optical tomography in the parallel plane transmission geometry: evaluation of a hybrid frequency domain/continuous wave clinical system for breast imaging.

Three-dimensional diffuse optical tomography (DOT) of breast requires large data sets for even modest resolution (1 cm). We present a hybrid DOT system that combines a limited number of frequency domain (FD) measurements with a large set of continuous wave (cw) measurements. The FD measurements are used to quantitatively determine tissue averaged absorption and scattering coefficients. The larger cw data sets (10(5) measurements) collected with a lens coupled CCD, permit 3D DOT reconstructions of a 1-liter tissue volume. To address the computational complexity of large data sets and 3D volumes we employ finite difference based reconstructions computed in parallel. Tissue phantom measurements evaluate imaging performance. The tests include the following: point spread function measures of resolution, characterization of the size and contrast of single objects, field of view measurements and spectral characterization of constituent concentrations. We also report in vivo measurements. Average tissue optical properties of a healthy breast are used to deduce oxy- and deoxy-hemoglobin concentrations. Differential imaging with a tumor simulating target adhered to the surface of a healthy breast evaluates the influence of physiologic fluctuations on image noise. This tomography system provides robust, quantitative, full 3D image reconstructions with the advantages of high data throughput, single detector-tissue coupling path, and large (1L) imaging domains. In addition, we find that point spread function measurements provide a useful and comprehensive representation of system performance.

Adult↗

PubMed2002

Bulk optical properties of healthy female breast tissue.

We have measured the bulk optical properties of healthy female breast tissues in vivo in the parallel plate, transmission geometry. Fifty-two volunteers were measured. Blood volume and blood oxygen saturation were derived from the optical property data using a novel method that employed a priori spectral information to overcome limitations associated with simple homogeneous tissue models. The measurements provide an estimate of the variation of normal breast tissue optical properties in a fairly large population. The mean blood volume was 34 +/- 9 microM and the mean blood oxygen saturation was 68 +/- 8%. We also investigated the correlation of these optical properties with demographic factors such as body mass index (BMI) and age. We observed a weak correlation of blood volume and reduced scattering coefficient with BMI: correlation with age, however, was not evident within the statistical error of these experiments. The new information on healthy breast tissue provides insight about the potential contrasts available for diffuse optical tomography of breast tumours.

Adult↗

PubMed2001

Optic disk characteristics before the occurrence of disk hemorrhage in glaucoma patients.

PURPOSE: To evaluate qualitatively the structural characteristics and the associated features that antedate the occurrence of a disk hemorrhage in patients with glaucoma. METHODS: Retrospective observational case series. A total of 4018 pairs of stereoscopic optic disk images obtained over 15 years were reviewed. All eyes with optic disk images before the occurrence of a disk hemorrhage were enrolled. The disk images were evaluated in a masked fashion with respect to the general neural rim and peripapillary appearance. RESULTS: The optic disk characteristics and associated features that most antedate the disk hemorrhage in 33 eyes of 26 patients that had previous optic disk images for evaluation are focal neural rim notch (36%), thin sloping rim (42%), peripapillary atrophy (79%), and superior-inferior rim asymmetry (73%). In eyes with preexisting focal rim notches, all subsequent disk hemorrhages were identified at or adjacent to the notches. CONCLUSIONS: Focal rim notching may precede the occurrence of a disk hemorrhage.

Aged↗

PubMed2000

Paired parallel locking forceps.

We describe an instrument used to prevent contact between an antimetabolite and the conjunctiva-Tenon's wound edge in filtering surgery. Paired parallel locking forceps were used to keep the everted conjunctival-Tenon's wound edge from touching the antimetabolite sponge during limbal-based filtering surgery while enabling manipulation of the antimetabolite sponge. This allows the surgeon to more easily avoid the conjunctival edge, making antimetabolite touch easier and safer.

Alkylating Agents↗

PubMed2000

Modeling photon transport in transabdominal fetal oximetry.

The possibility of optical oximetry of the blood in the fetal brain measured across the maternal abdomen just prior to birth is under investigation. Such measurements could detect fetal distress prior to birth and aid in the clinical decision regarding Cesarean section. This paper uses a perturbation method to model photon transport through an 8-cm-diam fetal brain located at a constant 2.5 cm below a curved maternal abdominal surface with an air/tissue boundary. In the simulation, a near-infrared light source delivers light to the abdomen and a detector is positioned up to 10 cm from the source along the arc of the abdominal surface. The light transport [W/cm2 fluence rate per W incident power] collected at the 10 cm position is Tm = 2.2 x 10(-6) cm(-2) if the fetal brain has the same optical properties as the mother and Tf = 1.0 x 10(-6) cm(-2) for an optically perturbing fetal brain with typical brain optical properties. The perturbation P=(Tf - Tm)/Tm is -53% due to the fetal brain. The model illustrates the challenge and feasibility of transabdominal oximetry of the fetal brain.

Abdomen↗