| 1779 Angular Dependence of Crack Detection using Radiography and Ultrasound | ||
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J.C. CHO1, M.O. CULJAT2, R.S. SINGH3, E.R. BROWN3, W.S. GRUNDFEST4, R.R. NEURGAONKAR5, D.C. YOON6, and S.N. WHITE1, 1UCLA School of Dentistry, Los Angeles, CA, USA, 2UCLA Dept of Bioengineering, Los Angeles, CA, USA, 3UCSB College of Engineering, Santa Barbara, CA, USA, 4UCLA Dept of Bioengineering, Los Angeles, USA, 5Rockwell Scientific Company, CA, USA, 6UCLA School of Dentistry, Los Angeles, USA Background: Diagnosis of cracked teeth is dependent on clinical assessment, not the use of imaging techniques. X-ray detection is limited to planar cracks that are nearly parallel to the beam. Objectives: To compare the angular dependence of crack detection of conventional radiography and a novel ultrasound imaging system. Methods: An idealized tooth phantom was prepared using glass to represent enamel and composite to represent dentin with a planar water-filled 25µm crack. Radiographs were made (70kV, 0.16s) at 0o, 2.5o, and 5o to the crack plane. For ultrasound, a novel monostatic pulse-echo system, digital signal processing, a 19 MHz single-element PLZT transducer with an 8o 3dB full beam width, and a Ga-In alloy couplant were used. The tooth was rotated relative to the ultrasound beam and output measurements made at 90o, 87.5o, and 85o. Results: Using radiography, a 0o beam orientation resulted in unequivocal radiographic crack delineation; at 2.5o the crack image was a blurred widened shadow; at 5o the crack was almost invisible. Ultrasound gave like results; at 90o crack detection was unequivocal; at 87.5o and 85o, the intensity of the crack echo decreased 7dB (80%) and 20dB (99%), respectively, relative to the crack intensity at 90o. Discussion: Like radiography, single-element monostatic pulse-echo ultrasound detection was highly angle dependent. Snell's Law predicts that electromagnetic waves are inherently more angle dependent than acoustic waves in teeth. Ultrasound angle dependence can be improved using sensors with large effective apertures, i.e. piezoelectric arrays; or a broader beam, but this has diminished lateral resolution and increased acoustic clutter. Unlike radiography, ultrasound can provide depth information, penetrate radiopaque restorations, is non-ionizing, can locate cracks smaller than the acoustic wavelength, and is favored by non-planar cracks. Conclusion: For detection of planar cracks, both conventional radiography and single element ultrasound transducers were highly angle dependant. NIH/NIDCR DE14189 | ||
| Seq #207 - Clinical Science 2:00 PM-3:00 PM, Saturday, 11 March 2006 Dolphin Hotel Pacific Hall | ||
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