Functional MRI

When we use our brain, the neurons and supporting structures involved require oxygen and nutrients to aid in optimal brain function. Blood flow changes are intimately linked to brain activation and can be measured using special MRI techniques. When we move our fingers or open and close our hands, there is increased blood flow to the motor area of the brain that exceeds the actual demand for oxygen. This overshoot of oxygenated blood relative to de-oxygenated blood results in a subtle change in signal on the order of 1.5% to 5% relative to the resting state. This small signal change can be detected using ultra-fast Echo Planar Imaging (EPI) sequences that allow an image to be obtained in as short as 40 milliseconds. The difference between the resting state and the activated state is then mapped onto a high resolution MRI image. This imaging technique allows for the detection of the primary visual, auditory, motor, and sensory cortices. In addition, fMRI also can study higher cortical activity such as memory, attention and speech.

• Functional MRI of Attention in Normal Volunteers Using a Modified PASAT Test: Effect of Test Difficulty on Activation
• Both Positive and Negative BOLD Signals Detected inj Brain Tumor Patients

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Diffusion Imaging

Subtle fluid changes in the brain are seen in various disease states. Routine MRI is sensitive to these fluid changes and has advanced medical treatment since its clinical inception. Diffusion imaging uses special manipulation of the magnetic field to allow for the detection of brain fluid changes that may not be apparent on routine images. This technique aids in the early detection of stroke injury that has the potential to differentiate the amount of brain permanently damaged during a stroke from the surrounding ishemic and potentially recoverable brain.

• Apparent Diffusion Coefficient Imaging

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MR Spectroscopy

• Proton Spectroscopy
  
  The spectroscopic evaluation of chemical substances has been performed using magnetic resonance for the past 30 years, far longer than magnetic resonance imaging. MR spectroscopy may also be obtained in some MRI units to evaluate the chemical make up of the brain without having to remove any tissue. This may be extremely helpful in differentiating changes from radiation necrosis or recurrent brain tumor, and detecting abnormal signal in the temporal lobes in patients with seizure or demyelination changes in the white matter.
  
  
  
• Phosphorus Spectroscopy
  
  P Magnetic Resonance Spectroscopy (MRS) was first demonstrated in 1974 when it was used to evaluate phosphorus metabolites in an intact, excised muscle preparation. Soon thereafter the technique was extended to in-vivo investigations through the use of surface coils. P MRS evaluates the relative concentrations of phosohorus nuclei present as inorganic phosphate (Pi), phosphocreatine (PCr), phosphomonoesters and phosphodiesters, and the nucleotide triphosphates, primarily adenosine triphosphate (ATP). This technique has been used extensively to study skeletal muscle at rest and to follow skeletal muscle changes during excercise by normal volunteers and by patients with a variety of diseases. Measurements taken of muscle pH and the ratios of PCr/Pi, Pi/ATP, and PCr/ATP in these studies have included evaluations both at rest and during excercise protocols.
  
  Further work has been directed towards the use of P MRS to measure intracellular free magnesium levels. Because uncomplexed ATP and free intracellular magnesium exist in equilibrium with complexed MgATP, the observable ATP chemical shifts are sensitive to changes in free intracellular magnesium levels. As a result, P MRS is capable of noninvasively measuring the biologically active form of magnesium in vivo.

• Intracellular Mg+2 and PCr/Pi Values are a Function of Gender and Exercise Status