Sentinel Lymph Nodes in the Rat: Noninvasive Photoacoustic and US Imaging with a Clinical US System

Abstract

Purpose:To evaluate in vivo sentinel lymph node (SLN) mapping by using photoacoustic and ultrasonographic (US) imaging with a modifi ed clinical US imaging system. Materials and Methods:Animal protocols were approved by the Animal Studies Committee. Methylene blue dye accumulation in axillary lymph nodes of seven healthy Sprague-Dawley rats was imaged by using a photoacoustic imaging system adapted from a clinical US imaging system. To investigate clinical translation, the imaging depth was extended up to 2.5 cm by adding chicken or turkey breast on top of the rat skin surface. Three-dimensional photoacoustic images were acquired by mechanically scanning the US transducer and light delivery fi ber bundle along the elevational direction. Results:Photoacoustic images of rat SLNs clearly help visualization of methylene blue accumulation, whereas coregistered photoacoustic/US images depict lymph node positions relative to surrounding anatomy. Twenty minutes following methylene blue injection, photoacoustic signals from SLN regions increased nearly 33-fold from baseline signals in preinjection images, and mean contrast between SLNs and background tissue was 76.0 6 23.7 (standard deviation). Methylene blue accumulation in SLNs was confi rmed photoacoustically by using the optical absorption spectrum of the dye. Three-dimensional photoacoustic images demonstrate dynamic accumulation of methylene blue in SLNs after traveling through lymph vessels. Conclusion:In vivo photoacoustic and US mapping of SLNs was successfully demonstrated with a modifi ed clinical US scanner. These results raise confi dence that photoacoustic and US imaging can be used clinically for accurate, noninvasive imaging of SLNs for axillary lymph node staging in breast cancer patients.q RSNA, 2010

Effects of the approximations of light propagation on quantitative photoacoustic tomography using two-dimensional photon diffusion equation and linearization

“…Angiogenesis in cancer tissues increases the concentration of hemoglobin, which increases the absorption coefficient [9][10][11][12][13][14][15]. Some contrast agent molecules and nanoparticles increasing the light absorption coefficient are useful for finding diseased tissues [16,17] and mapping the sentinel lymph nodes [18,19]. Therefore, QPAT reconstructing the absorption coefficient will be useful in medical diagnoses.…”

In vivo three-dimensional photoacoustic imaging based on a clinical matrix array ultrasound probe

“…PA imaging, however, provides a high ultrasonic spatial resolution for deep imaging by utilizing ultrasonic detection of the PA wave generated by absorbed diffuse light. 2,3 Deep PA imaging has been used to image both biological structure (e.g., internal organs, 4,5 and sentinel lymph nodes 6 ) and function (e.g., tumor hypoxia, 7 and brain oxygenation 8,9 ). The ability of PA imaging (PA microscopy and PA computed tomography 1 ) systems to render three-dimensional (3-D) volumetric images relies on recording the PA time-of-flight signals on a two-dimensional (2-D) surface facing the photoacoustic source, light-absorbing chromophores.…”

“…Due to the system cost and complexity when employing a large number of data acquisition (DAQ) channels, currently most PA imaging systems utilize a single-element ultrasound (US) transducer [7][8][9][10] or a one-dimensional (1-D) array US probe. [4][5][6]11 Mechanical scanning of the US probe required by these systems to form 3-D PA images limits the volumetric imaging frame rate. Thus, 3-D PA imaging systems using 2-D array US probes have been recently studied.…”

“…2 Our group previously reported a modified clinical US scanner using a linear US array for clinical translation of PA sentinel lymph node mapping. 6 In this report, we evaluated the performance of the matrix US array based multi-modal 3-D imaging system using a resolution phantom, and demonstrated 3-D in vivo PA SLN mapping in a rat model.…”

A 2.5-mm outer diameter photoacoustic endoscopic mini-probe based on a highly sensitive PMN-PT ultrasonic transducer

“…To date, a penetration depth more than ~1 cm has been demonstrated in human subjects [16][17][18] . Angiographic or lymphangiographic imaging capabilities are clinically relevant because such images can provide vital information for disease staging [18][19][20][21] . PAT can provide images with endogenous contrast or can be enhanced by numerous contrast agents 6,10 .…”