http://cds.ismrm.org/protected/13MPresentations/E225/ Go to 51:47-1:06 mark listen for 9 minutes

= γ = γ 2π 2π

Spin echo signal strength More Signal Loss when encoding for diffusion Diffusion of water used in Diffusion MRI Imaging and Diffusion Tensor Imaging (DTI) MRI Spin echo signal strength More Signal Loss when encoding for diffusion

Don’t let protons move -NO DIFFUISION y RF Gx Gy Gz - Time The rest of the sequence x Area under the gradients is b Don’t let protons move -NO DIFFUISION protons (Hydrogen) signal loss with DIFFUISION

= Dxx 1 0 0 Dxx Dxy Dxz 1 Dyx Dyy Dyz Dzx Dzy Dzz Y X Z D = Dxx Time 1 0 0 Dxx Dxy Dxz Dyx Dyy Dyz Dzx Dzy Dzz 1 D = Dxx = Dxx RF Gx Gy Gz - Time Y X Z Every voxel has a diffusion tensor to describe diffusion

1 1 0 Dxx Dxy Dxz 1 Dyx Dyy Dyz Dzx Dzy Dzz = ½(Dxx + 2Dyx + Dyy) Y X 1 1 0 Dxx Dxy Dxz Dyx Dyy Dyz Dzx Dzy Dzz 1 (½) = ½(Dxx + Dyx + Dxy + Dyy) = ½(Dxx + 2Dyx + Dyy) Y RF Gx Gy Gz - Time X Z

another stroke example Why diffusion another stroke example Diffusion Weighted Image Size of DTI ellipsoid Dead Perfusion Weighted Imaging Will Die Blood Volume Blood Flow Mean Transit Time Look for mismatch and find healthy tissue

Information available through DTI 2) Fiber tracking Information available through DTI Tract Monkey brain, in-vivo Pixel by pixel map of the diffusion ellipsoids in the ROI shown in the image. The Diffusion ellipsoids summarize all the information that we can obtain with DTI. This presentation is focused on the scalar ones, but we can clearly see the direction of the fibers in the corpus callosum.

Fiber tracking rat spine – T2 background post injury Diffusion Tensor Imaging Colored FA ADC Fiber tracking rat spine – T2 background post injury DWI T2 Fiber tracking mouse brain Pre injury Post injury

Functional Magnetic Resonance Imaging fMRI Functional Magnetic Resonance Imaging

The BOLD Effect Frequency spread causes signal loss over time Karen Miller Frequency spread causes signal loss over time BOLD contrast: Amount of signal loss reflects [dHb] Deoxygenated hemoglobin – unpaired iron electrons Contrast increases with delay (TE = echo time)

Vascular Response to Activation Karen Miller neuron capillary HbO2 HbO2 dHb HbO2 HbO2 dHb dHb = deoxyhemoglobin HbO2 = oxyhemoglobin [dHb] O2 metabolism blood flow Decreased deoxygenated larger signal in metabolically active regions blood volume

Language fMRI task Acquire Images when someone is processing language and when they are not. Subtract them. Colored areas are the signals that remain. Science Direct

Advanced Preoperative Neurosurgery MRI (unique to UKY in Kentucky) Function MRI – Listening to Music Temporal Lobe Epilepsy Surgery Young Girl – Aspiring Musician – Surgery Complete Success Motor (finger tapping) Language (word generation)

Spectroscopy

Forget about making an image, let’s look at hydrogen other than H20 inside the BIG RED VOXEL. Frequency

Frequency Frequency

More details – notice line splitting Extra chemical shift due to J coupling

Multi – Voxel Spectroscopy (aka Chemical Shift Imaging – CSI) Do many voxels at once Can be some disadvantages with signal to noise (S/N) and “voxel bleeding” (ie signal from one voxel may appear in neighboring voxels due to poor shim)

Can we image with other nuclei than hydrogen? We can image and do spectroscopy with other nuclei !!

Can even image with 23Na in Rat Brain (low resolution images are sodium 23 images) (high resolution images are hydrogen images) Need different hardware

31P Spectroscopy (again – need different hardware) Capable of detecting those key metabolites that play a role in tissue metabolism

13C Spectroscopy (again – need different hardware) Low sensitivity, but almost all metabolically relevant compounds contain carbon and large chemical shifts allow peak discrimination. Can infuse with 13C rich solution and follow metabolic pathway.