A comparison of pseudo-continuous arterial spin labelling and dynamic susceptibility contrast MRI with and without contrast agent leakage correction in paediatric brain tumours.

OBJECTIVE:: To investigate correlations between MRI perfusion metrics measured by dynamic susceptibility contrast and arterial spin labelling in paediatric brain tumours. METHODS:: 15 paediatric patients with brain tumours were scanned prospectively using pseudo-continuous arterial spin labelling (ASL) and dynamic susceptibility contrast (DSC-) MRI with a pre-bolus to minimise contrast agent leakage. Cerebral blood flow (CBF) maps were produced using ASL. Cerebral blood volume (CBV) maps with and without contrast agent leakage correction using the Boxerman technique and the leakage parameter, K2, were produced from the DSC data. Correlations between the metrics produced were investigated. RESULTS:: Histology resulted in the following diagnoses: pilocytic astrocytoma (n = 7), glioblastoma (n = 1), medulloblastoma (n = 1), rosette-forming glioneuronal tumour of fourth ventricle (n = 1), atypical choroid plexus papilloma (n = 1) and pilomyxoid astrocytoma (n = 1). Three patients had a non-invasive diagnosis of low-grade glioma. DSC CBV maps of T1-enhancing tumours were difficult to interpret without the leakage correction. CBV values obtained with and without leakage correction were significantly different (p < 0.01). A significant positive correlation was observed between ASL CBF and DSC CBV (r = 0.516, p = 0.049) which became stronger when leakage correction was applied (r = 0.728, p = 0.002). K2 values were variable across the group (mean = 0.35, range = -0.49 to 0.64). CONCLUSION:: CBV values from DSC obtained with and without leakage correction were significantly different. Large increases in CBV were observed following leakage correction in highly T1-enhancing tumours. DSC and ASL perfusion metrics were found to correlate significantly in a range of paediatric brain tumours. A stronger relationship between DSC and ASL was seen when leakage correction was applied to the DSC data. Leakage correction should be applied when analysing DSC data in enhancing paediatric brain tumours. ADVANCES IN KNOWLEDGE:: We have shown that leakage correction should be applied when investigating enhancing paediatric brain tumours using DSC-MRI. A stronger correlation was found between CBF derived from ASL and CBV derived from DSC when a leakage correction was employed.

Magnetic resonance spectroscopy in the assessment of pilocytic astrocytomas.

BACKGROUND: Pilocytic astrocytomas (PA) are common childhood brain tumours whose management and prognosis vary widely depending on location. (1)H magnetic resonance spectroscopy (MRS) measures biochemistry in vivo and shows promise for characterising brain tumours and aiding management. METHODS: Single voxel MRS (1.5 Tesla, TE 30 ms, TR 1500 ms) was performed on 27 children with PAs. Cases were designated 'progressors' if tumour progression led to their clinical management plan being altered. RESULTS: Prior to treatment, supratentorial tumours had significantly higher myo-inositol (p<0.01, t-test) and glutamate plus glutamine (p=0.02, t-test) than cerebellar tumours. Optic pathway or thalamic tumours that progressed had a significantly (p=0.04, t-test) lower myo-inositol at initial MRS than those with stable disease. Myo-inositol levels decreased significantly in progressors between the initial and subsequent MRS (p=0.03, paired t-test). Changes in myo-inositol occurred before clinical and radiological progression. CONCLUSIONS: MRS identifies differences with anatomical location in PAs and yields potential non-invasive biomarkers of prognosis.

The use of short-echo-time 1H MRS for childhood cerebellar tumours prior to histopathological diagnosis.

BACKGROUND: Proton magnetic resonance spectroscopy (MRS) measures concentrations of metabolites in vivo and provides a powerful method for identifying tumours. MRS has not entered routine clinical use partly due to the difficulty of analysing the spectra. OBJECTIVE: To create a straightforward method for interpreting short-echo-time MRS of childhood cerebellar tumours. MATERIALS AND METHODS: Single-voxel MRS (1.5-T Siemens Symphony NUM4, TR/TE 1,500/30 ms) was performed at presentation in 30 children with cerebellar tumours. The MRS results were analysed for comparison with histological diagnosis. Peak heights for N-acetyl aspartate (NAA), creatine (Cr), choline (Cho) and myo-inositol (mIns) were determined and receiver operator characteristic curves used to select ratios that best discriminated between the tumour types. The method was implemented by a group of clinicians and scientists, blinded to the results. RESULTS: A total of 27 MRS studies met the quality control criteria. NAA/Cr >4.0 distinguished all but one of the astrocytomas from the other tumours. A combination of Cr/Cho <0.75 and mIns/NAA <2.1 separated all the medulloblastomas from the ependymomas. CONCLUSION: Peak height ratios from short-echo-time MRS can accurately predict the histopathology of childhood cerebellar tumours.

Magnetic resonance spectroscopy suggests key differences in the metastatic behaviour of medulloblastoma.

BACKGROUND: Metastatic medulloblastoma has a poorer prognosis than localised disease in part due to inherent properties of the tumour. 1H magnetic resonance spectroscopy (MRS) provides a powerful method for investigating tumour metabolism in vivo. METHODS: Magnetic resonance imaging and short echo time (Te 30 ms) single voxel MRS were performed on the primary tumour of 16 children with medulloblastoma prior to surgical resection. Tumour volumes were calculated using a segmentation technique and the MRS was analysed using LCModel. RESULTS: Patients with metastatic disease had primary tumours which were smaller (p=0.01), had higher levels of total choline (p=0.03) and lower levels of mobile lipids (p=0.04). CONCLUSION: Metastatic medulloblastomas have metabolite profiles indicative of increased cell growth and decreased cell death compared with localised tumours reflecting intrinsic differences in underlying biology. Localised tumours with an MRS metabolite profile similar to those with metastatic disease may be at increased risk of metastatic relapse.