Functional neuroimaging in the assessment of CNS neoplasms

Dynamic Susceptibility Contrast Magnetic Resonance Imaging Protocol of the Normal Canine Brain

Perfusion magnetic resonance imaging (MRI), specifically dynamic susceptibility MRI (DSC-MRI) is routinely performed as a supplement to conventional MRI in human medicine for patients with intracranial neoplasia and cerebrovascular events. There is minimal data on the use of DSC-MRI in veterinary patients and a DSC-MRI protocol in the veterinary patient has not been described. Sixteen normal dogs, 6 years or older were recruited for this study. The sample population included 11 large dogs (>11 kg) and 5 small dogs (<11 kg). DSC-MRI was performed on a 1.5-T MRI using an adjusted protocol inherent to the MRI. Contrast media was injected using an automatic power injector. Injections were made after five MR measurements were obtained. Following image acquisition, an arterial input function (AIF) graph mapping the transit time of contrast within the cerebral arteries was generated. The manually selected time points along this graph were used to compute perfusion maps. A dose and rate of 0.1 mmol/kg gadolinium-based contrast media at 3 ml/s followed by 10 ml saline flush at 3 ml/s was used in all dogs greater than 11 kg. In all dogs >11 kg, a useable AIF and perfusion map was generated. One dog less than 11 kg received the same contrast dose and rate. In this patient, the protocol did not generate a useable AIF. The remainder of the dogs less than 11 kg followed a protocol of 0.2 mmol/kg gadolinium-based contrast media at 1.5 ml/s with a 10 ml saline flush at 1.5 ml/s. A useable AIF and perfusion map was generated in the remaining dogs <11 kg using the higher contrast dose and slower rate protocol. This study establishes a contrast dose and administration rate for canine DSC-MRI imaging that is different in dogs greater than 11 kg compared to dogs less than 11 kg. These protocols may be used for future applications to evaluate hemodynamic disturbances in canine intracranial pathology.

Assessment of Irradiated Brain Metastases by Means of Arterial Spin-Labeling and Dynamic Susceptibility-Weighted Contrast-Enhanced Perfusion MRI

RATIONALE AND OBJECTIVES

To assess if preradiation and early follow-up measurements of relative regional cerebral blood flow (rrCBF) can predict treatment outcome in patients with cerebral metastases and to evaluate rrCBF changes in tumor and normal tissue after stereotactic radiosurgery using arterial spin-labeling (ASL) and first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) perfusion MRI.

METHODS

In 25 patients with a total of 28 brain metastases, DSC MRI and ASL perfusion MRI using the Q2TIPS sequence were performed with a 1.5-T unit. Measurements were performed prior to and at 6 weeks, 12 weeks, and 24 weeks after stereotactic radiosurgery. Follow-up examinations were completely available in 25 patients for Q2TIPS and 17 patients with 18 metastases for DSC MRI. The rrCBF of the metastases and the normal brain tissue was determined by a region-of-interest analysis. rrCBF values were correlated with the treatment outcome that was classified according to tumor volume changes at 6 months.

RESULTS

The alteration of the rrCBF at the 6-week follow-up was highly predictive for treatment outcome. A decrease of the rrCBF value predicted tumor response correctly in all metastases for Q2TIPS and in 13 of 16 metastases for DSC MRI. The pretherapeutic rrCBF was not able to predict treatment outcome. The rrCBF values in normal brain tissue affected by radiation doses less than 0.5 Gy remained unchanged after therapy.

CONCLUSION

These preliminary results suggest that ASL and DSC MRI techniques determining rrCBF changes in brain metastases after stereotactic radiosurgery allow the prediction of treatment outcome.

Assessment of brain metastases with dynamic susceptibility-weighted contrast-enhanced MR imaging: initial results

PURPOSE

To assess if preradiation and early follow-up regional cerebral blood volume (CBV) measurements can help predict treatment outcome in patients with cerebral metastases and to evaluate regional CBV changes in tumor and normal tissue after radiosurgery.

MATERIALS AND METHODS

In 18 patients, dynamic susceptibility-weighted contrast material-enhanced magnetic resonance (MR) imaging was performed with a 1.5-T unit, which allowed an absolute quantification of the regional CBV. Measurements were performed prior to and at 6 weeks and 3 months after therapy. Treatment outcome was classified according to tumor volume changes at 6 months. The regional CBV of the metastases and the normal adjacent brain tissue were determined with a region-of-interest analysis. Regional CBV values were correlated with the patient outcome to assess the sensitivity and specificity of dynamic susceptibility-weighted contrast-enhanced MR imaging.

RESULTS

The pretherapeutic regional CBV was not able to help predict a treatment outcome; however, the method proved to be highly sensitive and specific for treatment outcome prediction at the 6-week follow-up. A decrease of the regional CBV value helped predict the treatment outcome with a sensitivity of more than 90%. The tumor volume change alone had a sensitivity of only 64%. The measured regional CBV values of normal brain tissue and their ratio were comparable to physiologic data and remained unchanged with therapy.

CONCLUSION

The results suggest that dynamic susceptibility-weighted contrast-enhanced MR imaging is a useful method for the assessment of radiosurgically treated brain metastases. The implemented technique with determination of the arterial input function enables an absolute quantification of the regional CBV and prediction of tumor response.

Cerebral perfusion imaging using contrast-enhanced MRI

New developments in fast magnetic resonance imaging (MRI) have enabled imaging of cerebral haemodynamics. This article describes the theory behind perfusion imaging and provides an overview of the most commonly used MRI technique. Limitations of this technique are described, and the potential clinical applications are discussed, with particular attention to the role of perfusion imaging in the context of stroke and brain tumour.