One can improve the performance of image reconstruction using more accurate models of the acquisition physics (e.g. finite resolution, energy spectrum: "MBIR"). However, this makes the reconstruction task also more complicated. Many methods have been proposed, which combine preprocessing based on physics with fast reconstruction using FBP. Even better reconstructions can be obtained by integrating the model into the iterative reconstruction algorithm, but at the cost of increased computation times. Major changes in the treatment of head and neck neoplasms encompass the advances of endoscopic-based surgical techniques, mainly for nasosinusal and laryngeal tumours, and the application of sophisticated radiation therapy techniques, combined with chemotherapy. As most tumours arise from the mucosa of the upper aero-digestive tract, clinical surveillance is necessary to detect superficial recurrences, while morphological and 'functional' imaging techniques are indispensable to detect subclinical extra-mucosal and nodal recurrences. How can imaging techniques discriminate recurrence, inflammation, necrosis or scar? Key points include the knowledge of the normal appearance of tissues (morphology & signals) on CT and MRI after surgery and chemo-radiotherapy. Specifically, when non-surgical treatment has been used, it means to become familiar with the expected changes both of tumour and adjacent tissues. Changes that can be asymmetric as extremely precise techniques of dose delivering are used, like tomotherapy. Morphologybased imaging techniques are often inadequate to discriminate small recurrences from vascularised scar tissue (enhancing). CT or MRI requires to be integrated by information provided by functional-based imaging techniques, FDG-PET-CT being the most established. Recently, a great interest among radiologists is focused on the application of DCE-CT or DCE-MRI and DWI-MRI in the follow-up of head and neck neoplasms. In fact, several studies have credited these techniques for providing functional information about tissues (perfusion, water exchange) that correct reporting of the necessary measurements targeted at the clinicians' need. Furthermore, MDCT scan protocol design will be reviewed, focusing not only on optimal implementation of common scan parameters but also on the need of ECG-triggering and its consequences. Finally, we will present the current status of evidence on using MDCT in PAVR procedures, and discuss future challenges and perspectives. CT remains a particular focus for efforts in radiological protection owing to its steadily increasing clinical application and the relatively high patient doses. Dosimetry is an essential element within good CT practice in order to allow the assessment of typical radiation risks in support of the justification of procedures and the routine monitoring and comparison of typical doses in pursuit of the optimisation of patient protection. The practical basis for dosimetry in contemporary CT remains the (updated) CT dose index (CTDI100), measured in either free air or the standard CT dosimetry phantoms. These latter measurements underpin the dose indicators commonly displayed by the CT scanner: volume-weighted CT dose index (CTDIvol) and dose-length product (DLP). Whereas these quantities are not patient doses, they nevertheless provide useful characterisation of each CT exposure in order to allow comparison of practice and facilitate improvements in patient protection. Typical levels of CTDIvol and DLP at each CT centre, periodically determined as the mean values observed for representative samples for each patient group and type of examination (and associated clinical indication), should be adopted as local diagnostic reference levels (DRLs). These should be subject to periodic review and compared with both corresponding national DRLs and also practice at other CT centres in pursuit of optimised patient protection. When required, estimates of typical organ and effective doses to reference patients from standard CT examinations can be made on the basis of appropriate dose coefficients normalised to the dose indicators (CTDIair, CTDIvol or DLP). Recent advances have generated renewed interest in dual energy CT. This presentation will discuss the basic principles, and the strengths and limitations of the techniques and implementations, of multi-energy methods for material characterisation. Conventional CT is at best an image of the linear attenuation coefficient at one energy and cannot uniquely identify tissue. Materials with different atomic numbers have different energy-dependent attenuation. Multi-energy imaging measures attenuation at different energies to more fully characterise materials. An important limitation is the fact that in the diagnostic energy range the attenuation of all materials is dominated by Compton scattering and photoelectric absorption, and unless there is a K-edge in the spectrum used, these phenomena have the same energy dependence for all materials. Thus, there are only two "basis functions" and spectral CT essentially measures effective atomic number and electron density. While there is residual ambiguity, it still provides important information. The main requirement for dual energy CT is to measure data using two spectra using multiple kVp and/ or filtration or methods in which the x-ray energy discrimination is performed at B S117 C D E F G H The spectrum of differential diagnoses is broad in the liver. Therefore, incidentally discovered liver lesions represent a challenging clinical situation. Fortunately, there are specific imaging features for the most common benign and malignant liver lesions (like, e.g. haemangioma, FNH, cysts, vascular pseudolesions, HCC, metastases) so that a minimal-invasive diagnosis with a biopsy in not needed in a lot of cases. In ultrasound the echogenity and recently also the contrast agent behaviour is used for liver lesion characterisation. In CT attenuation and also contrast agent behaviour are used for characterisation. MR imaging offers several options including T1-and T2 weighted images, use of chemical shift imaging, GRE sequences with long echoes and diffusion weighted images, so that tissue components like fat, water, glycogen, iron, etc. can be evaluated already in the pre-contrast examination. Beside the evaluation of dynamic signal characteristics in the early dynamic phase after contrast agent application, MR can utilise also tissue-specific contrast agents dedicated to the RES or to the haepatocytes. Other modalities like angiography, PET or other nuclear medicine methods usually only play a minor role nowadays in the evaluation of incidental liver lesions in non-oncological patients. In oncological patients the clinical consequences and also the range of diagnoses and pre-test probabilities are different from those of the non-oncological group; therefore, the demands to imaging are even higher. In case of atypical presentation of otherwise benign liver lesions like sclerosed haemangioma close follow-up or even biopsy can be necessary in such a setting. In recent years there has been a major change in the way patients presenting with haematuria are investigated, particularly in relation to imaging. This has been mainly influenced by the significant advances in CT and MR technology, and the introduction of CT Urography which is now considered one of the reliable imaging modalities. The role of IVU and ultrasound has been relegated to a complementary role, to some extent problem solving rather than their past essential role. The role of IVU in imaging patients with haematuria is therefore limited to very specific circumstances as follows: a) lack of access to CT or MR, b) stone localisation in some cases to demonstrate the calyceal anatomy and c) chronic pyelonephritis. Ultrasound imaging remains, however, the first line investigation for patients with microscopic haematuria and a useful adjunct to CT in the investigation of frank haematuria: a) characterisation of renal lesions, b) follow-up of known lesions and c) follow-up of renal trauma. diarrhoea, vomiting, constipation and abdominal pain. The differential diagnosis includes acute complications of treatment, complications or progression of the primary tumour, metastatic spread of tumour and problems related to co-morbid conditions. In this presentation I will illustrate these principles in two situations, one generic and acute and one more specific with subacute and chronic problems; the neutropaenic patient after chemotherapy or bone marrow transplantation; following radical chemoradiotherapy for cervical cancer.