T Imaging of Brain Tumours

A. Di COSTANZO, F. Trojsi, T. PopoLizio, G. M. Giannatempo, A. Simeone, S. Pollice, D. Catapano, M. Tosetti, N. Maggialetti, V. A. d'Angelo, A. Carriero, U. Salvolini, G. Tedeschi, T. Scarabino

Conventional MRI, or CT scanning if MRI is not available or contraindicated, is the method of choice for the non-invasive assessment of suspected intracranial tumours, but has limited sensitivity and specificity [1, 2]. In the past 20 years, there have been great advances in diagnostic imaging procedures with increasing accuracy of preoperative assessment of brain neoplasms. Proton magnetic resonance spectroscopic imaging, diffusion-weighted imaging and perfusion-weighted imaging all have contributed to an improvement of sensitivity and specificity in the diagnosis and monitoring of primary brain tumours.

Proton MR spectroscopic imaging ('H-MRSI) is a non-invasive technique that provides metabolic information from living tissues [3, 4]. Of the main metabolites of interest, choline (Cho) is found to be increased in areas of active membrane turnover, as in brain gliomas; N-acetylaspartate (NAA) is regarded as a marker of neuronal damage, destruction and/or dysfunction, and it is decreased whenever neurons are replaced by other cells; creatine (Cr) comprises signals from both phosphocreatine and creatine and is involved in energy metabolism; and lactate and/or lipids (LL) usually indicate necrosis [3, 4]. Several studies have demonstrated that 1H-MRSI can be used to guide surgical resection or biopsies, to define radiotherapy planning and monitor treatment effects, and to identify recurrence and progression of brain gliomas [3-10].

Diffusion-weighted imaging (DWI) is an MR technique sensitive to molecular motion of water within brain tissue, and provides information about compositional, structural, and organizational features of biological tissues [11]. A number of studies suggest that maps of the diffusion parameter called apparent diffusion coefficient (ADC), deriving information from cel-lularity and structural integrity, may play a role in the evaluation of brain tumours [12-17]. However, data about the distinction between different tumour types and grades [12,15,16], or between tumour infiltration and vasogenic oedema [12,17], are still conflicting.

Perfusion-weighted imaging (PWI) is an MR technique that looks into the haemodynamics of tumour tissue. The PWI measurement more frequently used is the relative cerebral blood volume (rCBV), which is di rectly correlated with microvessel density and tumour grade [18]. A number of studies have successfully used this technique in the preoperative classification and grading of brain tumours [18-22].

So far, all the above-mentioned MR techniques have been performed mainly using magnetic field strengths of 1.5 T. Higher magnetic field MR is expected to take advantage of the higher signal-to-noise ratio (SNR), and the improved spatial, temporal and spectral resolution [23, 24].

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