Current Clinical Concerns in CT: Results : Protocols
Temporal bones/IAC
1. I need a good internal auditory canal protocol for my new Phillips ultra Z CT machine. This is a single slice acquisition.
| Answer: I would use the thinnest slice possible at a spacing of .5 mm. |
2. What is the appropriate scan angle when doing axial temporal bones on a single slice scanner? Is angling +25 degrees to the Reid's base line correct?
| Answer: There are a range of different positions possible; however, in this era of 16 slice or volume scanning, positioning becomes less critical because of isotropic datasets. |
3. Do you sedate < 4 year old patients for CT TEMP BONE?
| Answer: With a 16 slice MDCT, the answer is usually there is no need, but sometimes we do. |
4. I'm looking for a protocol that visualizes temporal bones with and without contrast. We had a patient with some type of growth in the temporal region and I assume they were looking to see if there was any vascularity. The scanner we are using is a GE HiSpeed FX/i.
| Answer: You could do a CT angiogram with thin collimation and overlapping reconstructions. |
References
Caldemeyer KS, Sandrasegaran K, Shinaver CN, Mathews VP, Smith RR and Kopecky KK. Temporal bone: comparison of isotropic helical CT and conventional direct axial and coronal CT. AJR 1999; 172: 1675-1682.
- Summary: The utility of isotropic datasets was demonstrated in this study comparing 0.5 mm helical CT to 1 mm conventional CT. The isotropic datasets were superior for evaluation of the whole temporal bone and many individual structures.
- Summary: This study involved protocol optimization with a cadaveric phantom of the temporal bone, followed by application of the protocol for multislice CT on 38 patients. The HR kernels (FC 80-89), slice thickness (.5 to 1.0 mm), reconstruction intervals (0.2 - 0.3 mm) and mA (100 to 300) were varied for imaging the phantom. Source images, 2D and 3D reconstructions were evaluated for quality and diagnostic value. The authors report that the HR reconstruction algorithm was the most significant factor for image quality. The protocol selected for scanning patients included .5 mm slice thickness, .2 mm reconstruction interval, pitch factor of 3.5 and HR reconstruction algorithm (FC 81).