Frequency-domain techniques enhance optical mammography: initial clinical results

Abstract

We present a novel approach to optical mammography and initial clinical results. We have designed and developed a frequency-domain (110-MHz) optical scanner that performs a transillumination raster scan of the female breast in approximately 3 min. The probing light is a dual-wavelength (690 and 810 nm, 10-mW average power), 2-mm-diameter laser beam, and the detection optical fiber is 5 mm in diameter. The ac amplitude and phase data are processed with use of an algorithm that performs edge effect corrections, thereby enhancing image contrast. This contrast enhancement results in a greater tumor detectability compared with simple light intensity images. The optical mammograms are displayed on a computer screen in real time. We present x-ray and optical mammograms from two patients with breast tumors. Our initial clinical results show that the frequency-domain scanner, even at the present stage of development, has the potential to be a useful tool in mammography.

Figure 1

Schematic diagram of the frequency-domain LIMA. A radiofrequency oscillator (RF-Osc.) provides sinusoidally modulated current signals at two frequencies, namely f + Δf₁ and f + Δf₂ (f = 110 MHz, Δf₁ = 1 kHz, and Δf₂ = 0.8 kHz). These two signals supply two laser diodes (LD1 emitting at 690 nm and LD2 emitting at 810 nm) whose output beams (≈10 mW in power) are delivered to the breast. The radiofrequency oscillator also provides a signal at frequency f that modulates the gain of the detector. The frequency-domain raw data, ac amplitude and phase, are determined after signal processing of the detector output and are made available to the edge correction computer algorithm. The computer also controls the mechanical tandem scan of the laser beams and of the detector fiber, along the glass plates used for slight breast compression.

Figure 2

X-ray mammograms (A, craniocaudal; D, mediolateral) and optical mammograms (B, craniocaudal; E, mediolateral) based on the N parameter of a female left breast with a tumor. C (craniocaudal) and F (mediolateral) are the optical mammograms obtained using simple light intensity data and show the lower contrast of these images with respect to the N images. Specifically, this figure refers to a 55-year-old Caucasian woman with an invasive ductal breast cancer [UICC pT2 pN0 (0/29) M0 G2 L0 V0] in the left breast (lateral lower quadrant). The major tumor is 3.0 cm in diameter. Clinical examination, highly suspect; x-ray mammography, malignoma; breast ultrasound, malignoma. The dimensions of the breast portion shown in the x-ray mammograms are as follows: (A) craniocaudal projection, 18 cm (base width) × 11 cm (protrusion); (D) mediolateral projection, 18 cm (base width) × 10 cm (protrusion). We observe that the x-ray and optical images cannot be compared point by point because the degree of compression and the compression geometry are different in the x-ray and optical approaches.

Figure 3

X-ray mammograms (A, craniocaudal; D, mediolateral) and optical mammograms (B, craniocaudal; E, mediolateral) based on the N parameter of a female right breast with a tumor. C (craniocaudal) and F (mediolateral) are the optical mammograms obtained using simple light intensity data and show the lower contrast of these images with respect to the N images. Specifically, this figure refers to a 72-year-old Caucasian woman with an invasive ductal carcinoma of the breast, with a concomitant noninvasive ductal carcinoma in situ (UICC pT1a Nx M0 G2 L0 V0). The major tumor is 0.5 cm in diameter. Clinical examination, negative; x-ray mammography, slowly proliferating microcalcifications; in the craniocaudal mammogram, 0.5-mm suspect density correlating to microcalcifications. The dimensions of the breast portion shown in the x-ray mammograms are as follows: (A) craniocaudal projection, 18 cm (base width) × 12 cm (protrusion); (D) mediolateral projection, 18 cm (base width) × 9 cm (protrusion). We observe that the x-ray and optical images cannot be compared point by point because the degree of compression and the compression geometry are different in the x-ray and optical approaches.