ALADA Dose Optimization in the Computed Tomography of the Temporal Bone: The Diagnostic Potential of Different Low-Dose CT Protocols

Abstract

Objective: Repeated computed tomography (CT) is essential for diagnosis, surgical planning and follow-up in patients with middle and inner ear pathology. Dose reduction to “as low as diagnostically acceptable” (ALADA) is preferable but challenging. We aimed to compare the diagnostic quality of images of subtle temporal bone structures produced with low doses (LD) and reference protocols (RP). Methods: Two formalin-fixed human cadaver heads were scanned using a 64-slice CT scanner and cone-beam CT (CBCT). The protocols were: RP (120 kV, 250 mA, CTDIvol 83.72 mGy), LD1 (100 kV, 80 mA, CTDIvol 26.79 mGy), LD2 (100 kV, 35 mA, CTDIvol 7.66 mGy), LD3 (80 kV, 40 mA, CTDIvol 4.82 mGy), and CBCT standard protocol. Temporal bone structures were assessed using a 5-point scale. Results: A median score of ≥2 was achieved with protocols such as the tendons of m. tensor tympani (RP/LD1/LD2/CBCT) and m. stapedius (CBCT), the incudostapedial joint (RP/LD1/CBCT), the incudomalleolar joint (RP/LD1/LD2/CBCT), the stapes feet (RP/LD1/CBCT), the stapes head (RP/LD1/LD2/CBCT), the tympanic membrane (RP/LD1/LD2/CBCT), the lamina spiralis ossea (none), the chorda tympani (RP/LD1/CBCT), and the modiolus (RP/LD1/LD2/CBCT). Adaptive statistical iterative reconstructions did not show advantages over the filtered back projection. Conclusions: LD protocols using a CTDIvol of 7.66 mGy may be sufficient for the identification of temporal bone structures.

Spectral Shaping Via Tin Prefiltration in Ultra-High-Resolution Photon-Counting and Energy-Integrating Detector CT of the Temporal Bone

“…With acquisition settings based on our institutional stan-dards and previous literature on temporal bone EID-CT, the maximum dose reduction potential inherent in the PCD may be even greater with alternate tube potential settings. 5,30 It is important to note that lower kVp protocols with tin prefiltration (eg, Sn 100 kVp) were not included in this investigation, because they could not technically achieve the tube current-time product required for dose-equivalent comparison to 120 kVp and Sn 150/ 140 kVp protocols on either scanner. Although the energy spectrum of Sn 100 kVp is closer to that of standard 120 kVp imaging, which may be beneficial in patients with osteoporosis and for ultra-low-dose imaging tasks (eg, assessment of the paranasal sinuses), the maximum achievable radiation dose with this potential setting is far below the clinical standard for temporal bone CT. 19 Finally, it must be stated that 2 of the most advanced scanners were compared for this investigation, hence the presented image quality and radiation dose levels may not be replicable with most CT systems currently on the market.…”

“…3 Although lowering of the radiation burden remains one of the main goals in current CT research, dose reduction with the latest generation of energy-integrating multidetector and even cone-beam CT systems is hampered by constructional limitations that prevent scanners from reaching a higher geometric dose efficacy. 4,5 Ultra-high-resolution imaging in particular is limited with current detector models, because a mechanical comb filter needs to be deployed before the detector to narrow its aperture size and achieve the maximum resolution. 6 Nevertheless, dose reduction efforts in energy-integrating detector CT (EID-CT) have benefitted immensely from the introduction of spectral shaping via tin prefiltration in dual-source (and modern single-source) CT scanners.…”

Quantitative bone imaging biomarkers and joint space analysis of the articular Fossa in temporomandibular joint osteoarthritis using artificial intelligence models

“…The TMJ acquisition protocol was as follows: field of view (FOV) of 40 × 40 mm, 90 kVp, 5 mAs and scanning time of 30.8s. The limitation of the exposure to the smallest FOV possible is in accordance to the ALARA (as low as reasonably achievable) principle, and this radiation reduction to the patient, maintaining or even improving the level of precision and accuracy in the diagnosis, supports the concept "as low as diagnostically acceptable" (ALADA) (25). Imaging features of one condyle per patient were included to reduce possible bias due to non-specific side data in systemic biological samples and comorbidities, technical problems in the hr-CBCT image acquisition, and presence of unilateral TMJ OA.…”

Ultra-low-dose CBCT scan: rational map for ear surgery

“…High-resolution computed tomography (HRCT) is the gold standard for imaging the temporal bone. This method provides crisp, clear images of the bony structure with radiation doses ranging from 1.6 mSv for adults to 7.1 mSv for new-borns, an amount equivalent to 6–24 months of background radiation [ 8 , 12 ]. CBCT can produce images that are as good or even better [ 5 – 7 , 9 ].…”

“…As early as 15 years ago, Peltonen et al [5] demonstrated the substantial potential of CBCT for imaging the middle ear; however, multi-slice computed tomography (MSCT) is still the standard method. The most recent articles rank CBCT as equal or superior to MSCT in terms of image quality (IQ) and resolution [6][7][8]. However, these studies compared images of cadaver heads and are thus free of reallife motion artifacts.…”