The abnormal thermogram has been shown to be a reliable indicator of a high risk of breast cancer. Nevertheless, a
major weakness of current infrared breast thermography is its poor sensitivity for deeper tumors. Numerical modeling
for breast thermography provides an effective tool to investigate the complex relationships between the breast thermal
behaviors and the underlying patho-physiological conditions. We have developed a set of new modeling techniques to
take into account some subtle factors usually ignored in previous studies, such as gravity-induced elastic deformations of
the breast, nonlinear elasticity of soft tissues, and dynamic behavior of thermograms. Conventional "forward problem"
modeling cannot be used directly to improve tumor detectability, however, because the underlying tissue thermal
properties are generally unknown. Therefore, we propose an "inverse problem" modeling technique that aims to estimate
the tissue thermal properties from the breast surface thermogram. Our data suggest that the estimation of the tumor-induced
thermal contrast can be improved significantly by using the proposed inverse problem solving techniques to
provide the individual-specific thermal background, especially for deeper tumors. We expect the proposed new methods,
taken together, to provide a stronger foundation for, and greater specificity and precision in, thermographic diagnosis,
and treatment, of breast cancer.
Infrared thermography has been shown to be a useful adjunctive tool for breast cancer detection. Previous thermography
modeling techniques generally dealt with the "forward problem", i.e., to estimate the breast thermogram from known
properties of breast tissues. The present study aims to deal with the so-called "inverse problem", namely to estimate the
thermal properties of the breast tissues from the observed surface temperature distribution. By comparison, the inverse
problem is a more direct way of interpreting a breast thermogram for specific physiological and/or pathological
information. In tumor detection, for example, it is particularly important to estimate the tumor-induced thermal contrast,
even though the corresponding non-tumor thermal background usually is unknown due to the difficulty of measuring the
individual thermal properties. Inverse problem solving is technically challenging due to its ill-posed nature, which is
evident primarily by its sensitivity to imaging noise. Taking advantage of our previously developed forward-problemsolving
techniques with comprehensive thermal-elastic modeling, we examine here the feasibility of solving the inverse
problem of the breast thermography. The approach is based on a presumed spatial constraint applied to three major
thermal properties, i.e., thermal conductivity, blood perfusion, and metabolic heat generation, for each breast tissue type.
Our results indicate that the proposed inverse-problem-solving scheme can be numerically stable under imaging noise of
SNR ranging 32 ~ 40 dB, and that the proposed techniques can be effectively used to improve the estimation to the
tumor-induced thermal contrast, especially for smaller and deeper tumors.
The alterations of the fornix in mild traumatic brain injury (mTBI) were investigated using diffusion tensor imaging
(DTI) and T1-weighetd anatomical imaging. The primary goal of this study was to test that hypothesis that the fornix
might play a major role in the memory and learning dysfunctions in the post-concussion syndrome, which may related
to the white matter (WM) degradations following mild traumatic brain injury. N=24 mTBI patients were longitudinally
studied in two time points with 6-month intervals using a 4-Tesla MRI scanner to measure the WM integrity of fornix
and the fornix-to-brain ratio (FBR), and compared with matched healthy controls. Our data show that the WM
degradation in fornix onset in the acute stage after mild TBI when the post-injury time was less than 6 weeks, and that
this WM degradation continued during the following 6-month period of recovery. In summary, using DTI and structural
MRI together can effectively detect the fornix changes in both cross-sectional and longitudinal investigations. Further
studies are warranted to exam the association between the fornix alterations and neurocognitive performance of TBI
patients.
Understanding the complex relationship between the thermal contrasts on the breast surface and the underlying
physiological and pathological factors is important for thermogram-based breast cancer detection. Our previous
work introduced a combined thermal-elastic modeling method with improved ability to simultaneously
characterize both elastic-deformation-induced and tumor-induced thermal contrasts on the breast. In this paper,
the technique is further extended to investigate the dynamic behaviors of the breast thermal contrasts during cold
stress and thermal recovery procedures in the practice of dynamic thermal imaging. A finite-element method
(FEM) has been developed for dynamic thermal and elastic modeling. It is combined with a technique to address
the nonlinear elasticity of breast tissues, as would arise in the large deformations caused by gravity. Our
simulation results indicate that different sources of the thermal contrasts, such as the presence of a tumor, and
elastic deformation, have different transient time courses in dynamic thermal imaging with cold-stress and
thermal-recovery. Using appropriate quantifications of the thermal contrasts, we find that the tumor- and
deformation-induced thermal contrasts show opposite changes in the initial period of the dynamic courses,
whereas the global maxima of the contrast curves are reached at different time points during a cold-stress or
thermal-recovery procedure. Moreover, deeper tumors generally lead to smaller peaks but have larger lags in the
thermal contrast time course. These findings suggest that dynamic thermal imaging could be useful to
differentiate the sources of the thermal contrast on breast surface and hence to enhance tumor detectability.
Fluid attenuated inversion recovery (FLAIR) detects the T2 prolongation in whiter matter lesions (WML) measured on
a macroscopic scale, whereas diffusion tensor imaging (DTI) more specifically detects the white matter (WM) integrity
alterations as measured by water diffusion on a microscopic scale. Both techniques have been widely used to evaluate
WM changes associated with aging, dementia and cerebral vascular disease, however, the relationship between white
matter lesions (FLAIR) and changes of DTI remains largely unknown. We addressed this issue using a voxel based
correlation analysis between DTI and FLAIR images acquired from 33 elderly subjects at 4T. The WML volume and
intensity were correlated the fraction anisotropy (FA) or mean diffusivity (MD) across all the subjects on a voxelwise
basis. Our results revealed that significant DTI-WML correlations occur at regions overlapping the major WML
distributions with moderate intensity, and that no significant correlations were detected in periventricular regions where
the FLAIR intensities are particularly high. We investigated WM degeneration as a continuum from normal WM to
cerebrospinal fluid (CSF) using a two-compartment WM model. The simulation results indicated that the FLAIR
intensity of WML reaches a maximum when the lesion severity is around 0.7, which is the same point where
correlations between DTI and WML disappear. Based on these findings, WM degeneration in elderly subjects may be
better characterized by using regional DTI-WML correlations in different stages of WM degeneration. DTI and FLAIR,
taken together improve specificity for characterization of WM degeneration than each measure alone.
The abnormal thermogram has been shown to be a reliable indicator of a high risk of breast cancer, but an open question
is how to quantify the complex relationships between the breast thermal behaviors and the underlying
physiological/pathological conditions. Previous thermal modeling techniques generally did not utilize the breast
geometry determined by the gravity-induced elastic deformations arising from various body postures. In this paper, a 3-D
finite-element method is developed for combined modeling of the thermal and elastic properties of the breast, including
the mechanical nonlinearity associated with large deformations. The effects of the thermal and elastic properties of the
breast tissues are investigated quantitatively. For the normal breast in a standing/sitting up posture, the gravity-induced
deformation alone is found to be able to cause an asymmetric temperature distribution even though all the thermal/elastic
properties are symmetrical, and this temperature asymmetry increases for softer and more compressible breast tissues.
For a tumorous breast, we found that the surface-temperature alterations generally can be recognizable for superficial
tumors at depths less than 20 mm. Tumor size plays a less important role than the tumor depth in determining the tumor-induced
temperature difference. This result may imply that a higher thermal sensitivity is critical for a breast thermogram
system when deeper tumors are present, even if the tumor is relatively large. We expect this new method to provide a
stronger foundation for, and greater specificity and precision in, thermographic diagnosis and treatment of breast tumors.
Current techniques substantially overestimate the dimensionality of group fMRI data, and this problem worsens
when principle component analysis (PCA) based data reductions are applied at multiple levels. In this paper, the
mechanism of the overestimation is investigated, and a new method is developed for more reliable dimensionality
estimation for group fMRI data at multiple levels. Simulation suggests that small variation of the signal components
within a group is a major cause of dimensionality overestimation. To obtain an improved estimation, appropriate
colored noise is added into the group fMRI data in order to blur the signal component variations. The noise
parameters are estimated from the original fMRI data, and the improved dimensionality is determined by applying a
first-order autoregressive (AR(1)) noise fitting technique to the PCA spectrum. The proposed method was tested on
group resting-state fMRI datasets acquired from 14 normal human subjects in 5 different sessions. The PCA-based
data reductions were performed at 3 levels in either "individual-session-subject" or "individual-subject-session"
order. Results indicate that the proposed method significantly reduces the dimensionality overestimation for multiple
level data reductions. Consistency of the estimated dimensionalities is observed with different group orders of the
data reduction.
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