Multimodal Diffuse Optical Imaging - Biomedical Optical Imaging Technologies: Design and Applications - page 362

quantitative functional information to calibrate BOLD signals and to monitor
accurately the oxygenation state of the tissue. To date, the clinical integration of
optical imaging with fMRI has been limited to brain imaging. Numerous studies
have demonstrated the good correlation both spatially and temporally between the
BOLD MRI and optical imaging [ 77 - 79 ]. Application of this approach to other
clinical scenarios such as functional imaging of tumors is ongoing [ 80 ].

10.5.2 Computer Tomography

Application of optical techniques to breast oncology has been one of the main
driving forces behind development in the field of diffuse optical imaging. While
some breast lesions are still discovered by palpation, the majority of breast cancer
diagnoses are made with X-ray mammography [ 81 ]. Therefore, the combination of
optical imaging with X-ray imaging is a logical step toward clinical acceptance of
optical imaging.
Hardware fusion of both techniques is not as challenging as MRI-optical fusion.
X-ray mammographers offer an open architecture that provides more flexibility to
couple optical hardware. However, in the case of breast examination, the acquisition
for both modalities should not be performed simultaneously but sequentially. Thus,
the challenge in the hardware fusion of both techniques resides in designing an
optical probe that can be mounted/unmounted on the X-ray compression plates in
minimal time but still with great precision for accurate registration and without
displacement of the breast.
The hardware fusion of X-ray and optical imaging is still very limited for clinical
applications. Figure 10.4 provides an overview of the system built at Massachusetts
General Hospital (MGH). In this implementation, an optical system based on both
CW and FD laser modules was integrated with a digital breast tomosynthesis (DBT)
imager [ 82 ]. The optical probes are embedded in anodized aluminum covers that
can be securely attached to an optically transparent cassette that is fastened to the
DBT system. The source and detector aluminum probes can be easily inserted in
the cassette and released prior to the X-ray scans without movement of the imaged
specimen. Such approach allows for true coregistration between the two modalities.
Then, spatial priors derived from the X-ray scans can be used to guide the inverse
optical problem. An example of a clinical examination performed with this dual-
modality system is provided in Fig. 10.4 .

10.5.3 Ultrasound

Ultrasound (US) is a well-established clinical modality in breast oncology used as
an adjunct to mammography to discriminate cyst from solid lesions. Ultrasound
is also a useful imaging modality to guide minimally invasive procedures such
as core needle biopsy [ 83 ]. Ultrasound imaging systems are based on a handheld