E³ 1726a - Functional imaging in head and neck radiology: beyond morphology
E³ 1726a - Functional imaging in head and neck radiology: beyond morphologySunday, March 5, 08:30 - 10:00 Room: N Session Type: E³ - ECR Master Class Topics: Nuclear Medicine, Physics in Medical Imaging, Oncologic Imaging, Head and Neck Moderator: M. M. Lemmerling (Ghent/BE) Add session to my schedule In your schedule (remove)
1. To understand the concept of diffusion in oncology.
2. To learn how to evaluate diffusion images and numeric values.
3. To understand new trends and restrictions of the method.
The apparent diffusion coefficient (ADC), obtained from DWI images, measures diffusion of water molecules in head and neck tumours. Many factors influence the ADC but in general malignant tumours show greater impairment of diffusion and lower ADC values compared to benign lesions. When used in the correct clinical context ADC aids MRI lesion characterisation. Lower ADCs are reported in metastatic compared to benign /reactive nodes; malignant salivary gland tumours compared to pleomorphic adenomas; malignancy compared to infection/ inflammation; lymphoma compared to squamous cell carcinoma (SCC); poorly compared to well differentiated SCC. However, ADC thresholds overlap and low ADC values occur in benign processes. The ADC of SCC shows associations with chemoradiotherapy response, an unfavourable outcome reported for tumours with high ADC pre-treatment, smaller %ADC rise early intra-treatment and low ADC post-treatment. ADC is obtained usually from a monoexponential model using b-values from 0 to 800/1000 sec/mm2, but the choice of b-values influences ADC values and provides diffusion parameters beyond ADC. Intravoxel incoherent motion (IVIM) uses lower b-values (~0-200 sec/mm2) to measure pseudodiffusion related to the microcirculation (D* and f) and higher b-values (~400-1000 sec/mm2) to measure pure diffusion (D). Diffusion kurtosis imaging extends the range to even higher b-values (>1000 sec/mm2) and takes into account non-Gaussian diffusion to obtain a diffusion parameter (Dapp) and also a kurtosis parameter (Kapp) which is believed to better reflect tumour heterogeneity and cell complexity. Methods of analysing the diffusion maps also are evolving to take into account tumour heterogeneity.
1. To review the clinical usefulness of perfusion imaging in head and neck.
2. To understand advantages and disadvantages of perfusion.
3. To become familiar with the value of perfusion imaging in monitoring the early effects of non-surgical treatment.
As chemo-radiation therapy is increasingly applied to head and neck cancer, there is a growing need to develop non-invasive surrogate-biomarkers to predict and assess the response to a non-surgical treatment. Therefore, imaging techniques exploring tumour properties other than CT density, T2-T1 weighting or the single-phase "static" enhancement pattern have been devised. These "functional techniques" aim at targeting tumour micro-architecture, perfusion and heterogeneity (texture analysis). In particular, CT and MR perfusion techniques have been developed to investigate the changes induced by neo-angiogenesis in the microcirculation of tumour. This has been accomplished by analysis of the kinetics of the passage through the tissues of a bolus of contrast agent (DCE-CT, DCE-MR) or of an endogenous bolus (blood, ASL-MR perfusion). These kinetics can be explored with different strategies to obtain visual information, semi-quantitative or quantitative parameters. Though quantitative parameters should reproduce tissue microvascular physiology more precisely than semi-quantitative parameters, they are less simple to calculate. Presently, most of the medical literature on perfusion analysis encompasses pilot studies only. In addition, these studies share several limitations, not only linked to the complexity of the physiological model used to extract quantitative parameters but also correlated to the variety of the acquisition techniques, outcome measures as well calculation procedures. These limitations deter the reproducibility of results. Nevertheless, one emerging finding is that neoplasms showing great heterogeneity of a parameter like Ktrans are associated with a poorer prognosis; probably related to the presence of areas capable of surviving in conditions of hypoxia.
1. To become familiar with the technique of MR/PET.
2. To discuss the value of MR/PET in head and neck oncology.
3. To be aware of the possible pitfalls.
This lecture focuses on clinical applications of MR/PET in head and neck tumours with special emphasis on squamous cell carcinoma. First, principles of MR/PET are discussed and the current evidence regarding clinical feasibility, image quality, optimized imaging protocols and quantification with MRI-based attenuation algorithms in the head and neck are reviewed. Typical tumour manifestations are presented and the recent literature on the diagnostic performance of MR/PET in head and neck cancer is reviewed. The appearance of primary and recurrent squamous cell cancers, lymph node metastases and distant metastases on MR/PET is summarized and the appearance of benign lesions mimicking malignant tumours, such as scar tissue, granulation tissue, soft tissue necrosis and osteonecrosis is addressed. We present illustrative cases of multiparametric evaluations of malignant and benign lesions with MRI, diffusion-weighted imaging, perfusion and PET and we discuss the dilemma how to deal with discrepant multiparametric data.