At our institution a PCD-CT is used allowing high resolution imaging to better depict the temporal bone anatomy and to identify subtle pathologies with higher confidence. All temporal bone HRCT studies were interpreted by a board certified head and neck radiology specialist. Between January 2022 to January 2024 a total of 347 examinations were carried out using PCD-CT, with a median value of total dose-length production (tDLP) 274 mGy*cm ([Q1; Q3], [242; 313.5] mGy*cm).

Data acquisition technique: 

According to our protocol a  helical acquisition is performed of the skull base in supine position with a tube voltage of 120-140 kV, with a pitch of 0.85, and a rotation time of 0.5 sec. respectively, resulting in an effective dose of 0.5-0.74 mSv. In adherence to the As Low As Reasonably Achievable (ALARA) principle, throughout the acquisition process various radiation dose optimization functions are activated. The CARE Dose4D is set on “full” mode, with a CARE keV IQ level 194 (corresponding to effective mAs 175). These functions are based on the analysis of the patient's topogram, evaluating both antero-posterior and lateral dimensions of the patient's body size, with a focus on the X-ray attenuation characteristics [4].  

Intravenous contrast was not routinely used in the evaluation of mastoid air cells, or in case of hearing loss, although it was used in various cases: for the assessment of vascular pathologies (ex. dissection, malformations), vascularised tumors (ex. hemangiomas), or complication of otomastoiditis (ex. abscess formation, thrombosis) [5,6]. 

Reformats: 

From the acquired raw data, a standard series were reconstructed in an axial orientation, using  a dedicated bone algorithm with a kernel of head-regular 84 (Hr84), with a slice thickness of 1 mm, an increment of 1 mm, and quantum iterative reconstruction (QIR) with a strength level of 3 [7] (Figure 1). For a better visualization each side was reconstructed with a magnified, smaller field of view with a slice thickness of 0.2 mm and an increment of 0.1 mm (Figure 2). Based on the axial images standard coronal reformats were created perpendicular to the axial plane (Figure 3). 

In patients with cochlear implants 0.4 mm slice thickness offers a reduction in metallic artifact, however in our experience the loss of spatial resolution is greater than the benefit of the decreased metallic artifact compared to an acquisition with 0.2 mm slice thickness. Therefore a 0.2 mm slice thickness is used in all cases including patients with cochlear implants (Figure 4).

Other reformats ex. Poschl and Stenvers reformats are not created routinely, only in unequivocal cases. 

Pediatric patients: 

In case of neonates, or children under the age of 14, a low dose protocol is advised with a tube voltage of 70 kV, effective dose ranging between 0.17-0.28 mSv. The CARE Dose4D is set to manual, with a CARE keV IQ level of 60 (corresponding to effective mAs 117). Standard axial reformats are reconstructed with a slice thickness of 1.5 mm, and with a 1.5 mm increment respectively. Reconstructions of magnified images on both sides are executed with a slice thickness of 0.2 mm each with a corresponding 0.2 mm increment (Figure 5).

Despite the lower dosage, resolution is still adequate for a thorough assessment of temporal bones. Given the increased efficacy of low-dose HRCT protocols to two-view X-rays of the skull, we opted to substitute cochlear implant control imaging with low-dose HRCT [8]. 

In standard clinical practice, children undergo psychological preparation before the examinations, sedation is rarely required. It can be very helpful for the children to familiarize themselves with the examination room beforehand and touch the equipment. However in cases where a child is still unable to remain calm despite these measures, an X-ray is performed, or sedation can be used. Latter only occurred in one instance.