Validity of computed tomography in imaging thin walls of the temporal bone.
OBJECTIVE
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.


CONCLUSIONS
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 degrees 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 degrees, partial volume effects result in a progressively increasing magnification of bone thickness.
Ahlqvist
J B
JB
Department of Oral and Maxillofacial Radiology, Umeå University, Sweden.
Isberg
A M
AM
D016616:Cryoultramicrotomy; D004424:Ear Canal / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D005069:Evaluation Studies as Topic; D006801:Humans; D011857:Radiographic Image Interpretation, Computer-Assisted; D011861:Radiography, Dental; D012044:Regression Analysis; D013701:Temporal Bone / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D013704:Temporomandibular Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*