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Background: In the field of otorhinolaryngology, the paranasal sinuses and the middle and inner ear present a clinical challenge. Radiological methods offer a stable foundation for diagnostics and preoperative decisions in this context. While many studies have explored the prevalence of maxillary sinusitis of dental origin (MSDO), the use of MSDO detected on cone beam computed tomography (CBCT) scans, rather than conventional computed tomography (CT), is a relatively new approach to detect MSDO. CBCT, with its higher ability to assess bony details, is becoming a valuable tool in detecting MSDO. Photon-counting Computed Tomography (PCCT), a cutting-edge diagnostic imaging method, enables radiological examinations with high spatial resolution at a low radiation dose compared with conventional CT. However, the question of how much the dose can be reduced while maintaining still diagnostic value in radiological examinations remains unanswered.

Aims: This thesis aimed to further develop the use of radiology in the ear, nose and throat (ENT) medical field, which could impact how we interpret radiological findings to obtain useful clinical information. The objectives for this thesis were as follows: 1) to investigate the proportion of MSDO among patients with suspected sinusitis referred for radiological examination; 2) to compare the symptomatology of MSDO with sinusitis due to upper respiratory tract infection (URTI); 3) to develop a modular anthropomorphic phantom that could be used to evaluate the performance of radiological techniques in detecting pathology in the temporal bone (TB) region; and 4) to investigate whether the diagnostic quality of TB imaging is maintained even at significantly lower radiation doses using PCCT compared to conventional energy integrated computed tomography (EICT).

Material and methods: Paper I was a retrospective study in which our research team reviewed 303 CBCT sinus examinations and analysed the data to determine the prevalence of MSDO among patients with suspected sinusitis who had been referred for radiological examination.A retrospective study was conducted in Paper II, in which the medical records from 61 patients with maxillary sinusitis confirmed via CBCT were thoroughly reviewed. Two independent observers reviewed all cases; when the observers disagreed, the examinations were re-reviewed to reach a consensus, ensuring the reliability of the findings. For comparison, the patients were divided into MSDO and URTI sinusitis groups. Information including self-reported symptoms, clinical findings, and time between first medical contact to correct diagnosis were collected and compared between the groups, providing a comprehensive understanding of the differences between the two conditions.

In Paper III, a modular anthropomorphic phantom was constructed. '

To evaluate anatomical structures and image quality, the phantom was used in paper IV to scan 10 human TB specimens using PCCT and conventional CT systems.

Results: In paper I, we found that the prevalence of unilateral MSDO was 40 %. Maxillary sinus mucosal swelling adjacent to periapical destruction was found in 91 % of the studied patients.

In paper II, we found that the MSDO patients reported a foul odour and foul taste more often, and the time from their first symptom to the correct diagnosis was significantly longer. The URTI sinusitis patients reported toothache, bilateral facial pain, and symptoms associated with a cold more often than the MSDO patients. The accuracy of CBCT for detecting MSDO was 97%.

In paper III, we found that the radiological attenuation of the polyurethane (PUR) plastic and alginate plastic used for the phantom was similar to those of the soft tissues of a living human. The mean Hounsfield unit (HU) values of the CT slices representing tissue at the TB and brain level were comparable in the phantom and patient groups.

In paper IV, we found that reviewers preferred PCCT scans for the majority of structures being evaluated and for overall image quality. This was true even at a radiation dose below 15 % of that in the clinical EICT protocol.

Conclusion: The close relationship between dental infections and unilateral sinusitis should not be overlooked. MSDO differs from URTI sinusitis regarding symptoms and clinical findings, and should be suspected in patients with unilateral symptoms presenting little pain and experiencing a foul odour and/or foul taste. CBCT is a reliable method of detecting MSDO. The modular phantom developed in the third study can be used to evaluate examination methods in a set-up corresponding to a living human without exposing patients to radiation. Finally, PCCT was found to be superior to EICT in terms of image quality.