The Thickness and Texture of Temporal Bone in Brain CT Predict Acoustic Window Failure of Transcranial Doppler Jee-Hyun Kwon, MD, PhD Jong S. Kim, MD, PhD Dong-Wha Kang, MD, PhD Kyun-Seop Bae, MD, PhD Sun U. Kwon, MD, PhD ABSTRACT Background and Purpose: Although transcranial Doppler (TCD) is useful for evaluation and treatment of ischemic stroke, tem- poral acoustic window failure (TAWF) limits its application. We performed this study to reveal whether initial brain CT of acute stroke patients predicted TAWF. Methods: We performed TCD in 92 acute ischemic stroke pa- tients (57 males, aged 38-84 years) with brain CT scans. We measured the thickness (BTW) and evaluated the texture of the temporal bone in acoustic windows shown in the CT scan with the use of picture archiving and communication system. The bone mineral density (BMD) of the vertebral bodies, femurs, and whole body was also measured. Results: Doppler signals were adequately obtained in 121 (65.8%) of the 184 middle cerebral arteries (MCA) from both cerebral hemispheres. BTW and inhomogeneity of tempo- ral bone, besides age, sex, and hypercholesterolemia, was strongly correlated with TAWF. BMD was not directly corre- lated with TAWF, but inhomogeneous temporal bone was corre- lated with lower BMD scores. If the brain CT scan showed thick (BTW ≥ 2.7 mm) and inhomogeneous temporal bone, the pos- sibility of TAWF was 93.5%, while if brain CT scan showed thin (BTW < 2.7 mm) and homogenous temporal bone, it was only 5.4%. Conclusions: The texture as well as the thickness of the tempo- ral bone was the most important determinant of TAWF. When Received April 7, 2006, and in revised form June 30, 2006. Accepted August 2, 2006. From the Department of Neurology, Ulsan Univer- sity Hospital, University of Ulsan, College of Medicine (J-HK); Department of Neurology, Asan Medical Cen- ter, University of Ulsan, College of Medicine ( JSK, D- WK, SUK); and Department of Clinical Pharmacology, Asan Medical Center, University of Ulsan, College of Medicine, Seoul, Korea (K-SB). Address correspondence to Sun U. Kwon, MD, PhD, De- partment of Neurology, Asan Medical Center, Pungnap- dong 388-1, Songpagu, Seoul, Korea. E-mail: sukwon@ amc.seoul.kr. acute stroke patients had thin and homogeneous temporal bones in initial brain CT scan, TAWF was very rare, and loss of MCA signals on TCD specifically indicated the absence of blood flow in MCA. Key words: Transcranial Doppler, temporal acoustic window failure, thickness of the temporal bone, inhomogeneity, bone mineral density, hypercholesterolemia. Kwon J-H, Kim JS, Kang D-W, Bae K-S, Kwon SU. The Thickness and Texture of Temporal Bone in Brain CT Predict Acoustic Window Failure of Transcranial Doppler. J Neuroimaging 2006;16:347-352. DOI: 10.1111/j.1552-6569.2006.00064.x Transcranial Doppler (TCD) is a useful tool for the evaluation of intracranial vessels through transmitting ul- trasound beam through the temporal bone. Nowadays the clinical applications of TCD are expanding. Presence of microembolic signals on TCD predicts the outcome of symptomatic carotid stenosis, and monitoring of TCD en- hances thrombolysis in acute stroke patients. 1 However, TCD examination is unsuccessful in 5-23% of patients 2,3 because ultrasound cannot penetrate the temporal bone sufficiently enough to analyze intracranial hemodynam- ics. This temporal acoustic window failure (TAWF) is one of the major obstacles on the clinical application of TCD. If we can specifically predict TAWF using initial brain CT scan, we may save the precious time for thromboly- sis to differentiate occlusion of the middle cerebral artery (MCA) from TAWF when acute stroke patient has no signals from the temporal window. Transmission of the ultrasound beam through the cranium may depend on the structure of the skull as well as the thickness. Inho- mogenous matrix structure of the middle layer (cancel- lous bone, diploe) must have higher chance of attenuation and scattering of the ultrasound than homogenous struc- ture. From the commonness of TAWF in the aged popu- lation and in women, we postulated that (1) osteoporosis is one of the important causes affecting the change of tem- poral bone, (2) osteoporosis and thick temporal bone are Copyright ◦ C 2006 by the American Society of Neuroimaging 347