Photoacoustic Computed Tomography for Pre-Operative Reconstructive Flap Angiography

Photoacoustic Computed Tomography (PACT) is a novel, non-invasive imaging technique which can perform deep tissue imaging with high spatial resolution and optical contrast. The system utilizes short-pulsed lasers to generate photoacoustic waves in biological tissues. These are then detected by a 512-element full-ring transducer array, which allows for high spatial resolution, especially in deep tissues. In addition, PACT utilizes diffuse optical tomography, in which the light absorption of hemoglobin at visible or near-infrared wavelengths, provides excellent contrast for the imaging of human vasculature.

Prior studies of PACT imaging have evaluated this technique to image the human breast as an alternative modality for breast cancer screening as well as to image human extremities for the evaluation of vascular disease. The full-ring transducer array offers a significant advantage in spatial resolution, especially in deep tissues, over the standard linear arrays employed in the standard, widely-used handheld ultrasonic transducers. In addition, diffuse optical tomography allows for strong vascular contrast over a large field of view without the use of exogenous contrast agents.

Flap reconstructive surgery utilizes a patient's own soft tissues to recreate structures, fill large soft tissue defects, provide joint coverage, or perform other reconstructive operations. Examples of patients who would require flap reconstructive surgery include patients undergoing mastectomies and patients who have suffered from trauma with significant tissue loss. Tissue flaps have a defined blood supply which originate from the original site of the tissue. The flap can be compromised if the arterial supply or venous drainage is jeopardized during tissue transfer. Therefore, an accurate understanding of the blood supply of the tissue flap is crucial for successful flap reconstructive surgery.

Current pre-operative vascular imaging modalities for flap reconstructive surgery include handheld Doppler ultrasonography, magnetic resonance angiography (MRA), and the gold standard computed tomography angiography (CTA). Doppler ultrasonography is technician-dependent, inaccurate, and lacks optical contrast. MRA is expensive, requires a lengthy imaging time, and requires the administration of intravenous contrast. CTA is also expensive, also requires the administration of intravenous contrast, and requires the administration of ionizing radiation. PACT does not require the administration of intravenous contrast or ionizing radiation, and provides excellent spatial resolution and optical contrast. Therefore, PACT would be an optimal pre-operative vascular imaging modality for flap reconstructive surgery.