January 1999, Volume 28, Issue 1, Pages 13 – 19

Original Article

Validity of computed tomography in imaging thin walls of the temporal bone JB Ahlqvist1 & AM Isberg Department of Oral and Maxillofacial Radiology, Umeå University, Umeå, Sweden     1Author for correspondence: Department of Oral and Maxillofacial Radiology, Umeå University, SE-901 87 Umeå, Sweden

Keywords

tomography, X-ray computed;   temporal bone;   temporomandibular joint; ear canal

Abstract

Objectives: To evaluate the validity of computed tomography (CT) for reproduction of the bone margins of the temporomandibular joint (TMJ). Methods: Seven TMJ specimens were examined with a CT and then cryosectioned. The bone separating the TMJ from the middle cranial fossa, middle ear and external auditory canal was measured as the full width at half maximum (FWHM). Measurements were compared with the true thickness of the bone wall. Results: There was good agreement when the bone walls were thicker than 1 mm: accuracy was influenced only by the angle of the bone wall to the scanning plane. Conversely, bone walls thinner than 1 mm were reproduced with a magnification that increased with decreasing bone thickness. The difference increased further as the inclination of the bone wall became greater. Conclusion: Measurements performed at FWHM are reliable within ±10% for bone walls more than approximately 1 mm thick which form an angle of less than 35° to the perpendicular of the scanning plane. For bone walls thinner than 1 mm and for those thicker than 1 mm with an inclination exceeding approximately 35°, partial volume effects result in a progressively increasing magnification of bone thickness.

Received 19 June 1998; Accepted 15 September 1998

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