Towards nonionizing photoacoustic cystography

Normally, urine flows down from kidneys to bladders. Vesicoureteral reflux (VUR) is the abnormal flow of urine from bladders back to kidneys. VUR commonly follows urinary tract infection and leads to renal infection. Fluoroscopic voiding cystourethrography and direct radionuclide voiding cystography have been clinical gold standards for VUR imaging, but these methods are ionizing. Here, we demonstrate the feasibility of a novel and nonionizing process for VUR mapping in vivo, called photoacoustic cystography (PAC). Using a photoacoustic (PA) imaging system, we have successfully imaged a rat bladder filled with clinically being used methylene blue dye. An image contrast of ~8 was achieved. Further, spectroscopic PAC confirmed the accumulation of methylene blue in the bladder. Using a laser pulse energy of less than 1 mJ/cm2, bladder was clearly visible in the PA image. Our results suggest that this technology would be a useful clinical tool, allowing clinicians to identify bladder noninvasively in vivo.