UC San Diego

Periodontitis is a public issue and imaging periodontal pocket is important to evaluate periodontitis. Dental ultrasound imaging has been increasingly studied for the diagnosis of periodontitis. Previous studies showed that the distances between several anatomical landmarks including alveolar bone crest (ABC), cementoenamel junction (CEJ), and gingival margin (GM) are significantly different among the healthy and diseased groups. However, these works were limited to anterior teeth (incisors and canines) due to the bulky size of the transducer. Moreover, ultrasound imaing lack the contrast to resolve the periodontal probing depth (PPD) due to the lack of contrast. In this dissertation, I will focus on developing compact photoacoustic and ultrasound imaging techniques that aims at full-mouth periodontal imaging. In Chapter 1, I will demonstrate a simple, yet versatile method named “Scissors” to help synchronize ultrasound open platforms (UOPs) for photoacoustic imaging with improved imaging quality. Scissors is a programmed function that can cut or add a fixed delay to RF data and thus synchronize it before reconstruction for real time imaging. In Chapter 2, I will report a new method named interleave-sampled PA imaging that enables high-frequency imaging with a relatively low sampling rate, e.g., a 41.67-MHz sampling rate with a 30-MHz transducer. High-frequency photoacoustic (PA) imaging (>20 MHz) requires data acquisition (DAQ) with commensurately high sampling rate, which leads to hardware challenges and increased costs. This method harnesses two acquisitions at a low sampling rate to effectively double the sampling rate for high-frequency imaging. It modulates the delay of the light pulses and can thus be applied to any PA DAQ system. In Chapter 3, I will report a clinical “hockey-stick”-style transducer integrated with fibers for periodontal photoacoustic imaging, which allows us to measure the periodontal probing depth (PPD). The unique angle shape of hockey-stick transducer allows it to image more posterior teeth than regular linear transducers. We used cuttlefish ink to label the periodontal pocket as a photoacoustic contrast agent. We characterized the imaging system, and then measured the pocket depth of 35 swine teeth. Three raters evaluated the performance of the hockey-stick transducer. The measurements between the Williams probing (gold standard) and the photoacoustic methods were blinded but highly correlated. We showed a bias of ~0.3 mm for the imaging-based technique versus Williams probing. The minimum inter-reliability was over 0.60 for three different raters of varying experience suggesting that this approach to measure periodontal pocket is reproducible. Finally, we imaged the three pre-molars of a human subject. We could access additional upper and posterior teeth than conventional linear transducers. In chapter 4, we characterized a transducer that can image the entire human mouth including assessment of periodontal pockets via a combination of photoacoustic and ultrasound imaging. Unlike conventional transducer design, this device has a toothbrush-shaped form factor with a side-view transducer to image molars (total size: 1 x 1.9 cm). A laser diode was integrated as the light source to reduce the cost and size and facilitates clinical transition. The in vivo imaging of a molar of a periodontal patient demonstrated that the transducer could image in the posterior area of gum in vivo; the value determined by imaging was within 7% of the value measured clinically. In Chapter 5, we used a commercially available 9-MHz hockey-stick transducer for clinical periodontal imaging. The hypothesis is that the distances between several anatomical landmarks including alveolar bone crest (ABC), cementoenamel junction (CEJ), and gingival margin (GM) are significantly different among the healthy and diseased groups. Here, the unique angle design of the hockey-stick transducer allows it to image posterior teeth of patients. We imaged 13 subjects including 53 premolars, 30 molars, and 79 incisors and canines. The inter-examiner tests demonstrated that the clinical parameters obtained from ultrasound imaging with the hockey-stick transducer were reproducible. We further compared the measurements from ultrasound imaging and periodontal probing among periodontally healthy and diseased patients. Notably, the average imaging-based gingival recession (iGR) measurements were -1.12 mm (i.e., 1.12 mm above the CEJ) for gingivitis and Stage I periodontitis, and -0.56 mm for Stage III patients, demonstrating a significant increase of gingival recession in patients with severe periodontitis (Student t-test, unpaired, two-tailed, p < 0.0001). Our results showed that ultrasound imaging has value in periodontal diagnosis.