Handheld photoacoustic probe to detect both melanoma depth and volume at high speed in vivo

Abstract

We applied a linear-array-based photoacoustic probe to detect melanin-containing melanoma tumor depth and volume in nude mice in vivo. This system can image melanomas at five frames per second (fps), which is much faster than our previous handheld single transducer system (0.1 fps). We first theoretically show that, in addition to the higher frame rate, almost the entire boundary of the melanoma can be detected by the linear-array-based probe, while only the horizontal boundary could be detected by the previous system. Then we demonstrate the ability of this linear-array-based system in measuring both the depth and volume of melanoma through phantom, ex vivo, and in vivo experiments. The volume detection ability also enables us to accurately calculate the rate of growth of the tumor, which is an important parameter in quantifying the tumor activity. Our results show that this system can be used for clinical melanoma diagnosis and treatment in humans at the bedside. Linear-array-based PA images of melanoma acquired in vivo on day 3 (a) and day 6 (b).

Keywords: handheld; melanoma; photoacoustic; rate of growth.

Fig. 1

Schematic diagram of the LZ250 linear transducer array with optical fiber bundle integrated. (a) View from the elevational direction (x). (b) View of the transducer array's head (enclosed by a dashed box in (a)) from the lateral direction (y).

Fig. 2

Simulation of the single focused ultrasonic transducer and the linear array. (a) Preset energy deposition distribution (A_e). Recovered A_e by the single focused ultrasonic transducer (b) and by the linear array transducer (c).

Fig. 3

Response characteristics of the linear-array probe. (a) Maximum amplitude projection of the two crossed 6-μm-diameter carbon fibers. The diameters differ because of the directional resolution differences. (b) Cross-section image of the vertical carbon fiber along the dashed line in (a). Experimental data and Gaussian fits of the PA amplitude distributions along the (c) x, (d) y, and (e) z directions.

Fig. 4

Linear-array-based PA images of melanoma phantoms. (a) Photo of the melanoma phantoms. (b1-b7) and (c1-c7) correspond to the melanoma phantoms 1-7 in (a). Melanoma phantom images acquired by PA (b1-b7) and a standard optical microscope (c1-c7).

Fig. 5

Depth (a) and volume (b) quantification of melanoma phantoms. Blue dots: experimental measurements. Red lines: ideal line if the PA measurements are identical to the standard measurements.

Fig. 6

Linear-array-based PA images of ex vivo melanomas. (a) A photo of the ex vivo melanomas. (b1-b6) and (c1-c6) correspond to the melanoma phantoms 1-6 in (a). Melanoma images acquired by PA (b1-b6) and a standard optical microscope (c1-c6).

Fig. 7

Depth (a) and volume (b) quantification of ex vivo melanomas. Blue dots: experimental measurements. Red lines: ideal line if the PA measurements are identical to the standard measurements.

Fig. 8

Linear-array-based PA images of melanoma acquired in vivo on day 3 (a) and day 6 (b).