page_title: Thermoacoustic imaging
section_title: Linear array
hierarchical_section_title: Thermoacoustic imaging / Image formation principles / Detector geometries / Linear array
caption_attribution_description: English: Illustration of a linear transducer array
context_page_description: Thermoacoustic imaging was originally proposed by Theodore Bowen in 1981 as a strategy for studying the absorption properties of human tissue using virtually any kind of electromagnetic radiation. But Alexander Graham Bell first reported the physical principle upon which thermoacoustic imaging is based a century earlier. He observed that audible sound could be created by illuminating an intermittent beam of sunlight onto a rubber sheet. Shortly after Bowen's work was published, other researchers proposed methodology for thermoacoustic imaging using microwaves. In 1994 researchers used an infrared laser to produce the first thermoacoustic images of near-infrared optical absorption in a tissue-mimicking phantom, albeit in two dimensions. In 1995 other researchers formulated a general reconstruction algorithm by which 2D thermoacoustic images could be computed from their "projections," i.e. thermoacoustic computed tomography. By 1998 researchers at Indiana University Medical Center extended TCT to 3D and employed pulsed microwaves to produce the first fully three-dimensional thermoacoustic images of biologic tissue [an excised lamb kidney ].
context_section_description: Linear transducer arrays (both curved and straight) are commonly used in conventional medical ultrasound. They are available in a wide variety of sizes and shapes. They are easily adapted for use in thermoacoustic imaging. Figure 7 illustrates how a linear array is used for 2D thermoacoustic imaging. The array consists of a number of elements (64 - 256) that are focused in the vertical dimension to maintain maximum sensitivity within a 2D plane extending outward from the front face of the array. Thermoacoustic signals within the plane are localized by calculating the times-of-flight from each position within the plane to each element of the array (arrows, Fig. 7).
caption: Fig. 7: Linear transducer array used to image a 2D plane.
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