Diffusion Physics H 2 O in the body is always in random motion due to thermal agitation B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

- Diffusion Coefficient is dependent on Temperature and Viscosity of Tissue Diffusion Coefficient (rate of motion) Temperature Size of Molecule Viscosity Diffusion Physics B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

-The “rate” of water motion is determine by a diffusion coefficient, “D”. -Mean displacement of water molecules is related to “D” by Einstein’s equation: TimeDiffusion Coefficient Mean Displacement Diffusion Physics B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

Detecting Diffusion with MRI - Intravoxel Incoherent Motion Ellingson et al., Concepts in MR, 2008 B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 From: Ellingson, Concepts in MR, 2008

Detecting Diffusion with MRI - Intravoxel Incoherent Motion Detected DWI Signal MRI Signal w/o Diffusion Sensitivity Variability in Phase of “Tagged” H 2 O Level of Diffusion Weighting Diffusion Coefficient B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

Intravoxel Incoherent vs Coherent Motion B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Diffusion Effects (Incoherent) Flow Effects (Coherent) -- Phase Contrast (PC)-MRI d  =  /3 radians  Velocity

Proton on H 2 O Image Voxel  = t 1  = t 2  = t 3 MRI Signal Diffusion Time (or level of diffusion weighting) B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

Factors that affect diffusion coefficient, D Diffusion Time, t -Physical time between gradients used to “tag” H 2 O B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

Factors that affect diffusion coefficient, D Size of Compartment(s) - If we set a limit for  r, then we observe an apparent diffusion coefficient, ADC B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Physical Compartment Size Expected Compartment Size

Factors that affect diffusion coefficient, D Tortuosity of the Compartments - More tortuous paths look like slow diffusion B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Tortuosity Actual Path Expected Path

Factors that affect diffusion coefficient, D Viscosity and Temperature B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Diffusion Coefficient (rate of motion) Temperature Viscosity Pure H 2 OCSFInfection (WBCs)Lymphoma

Factors that affect diffusion coefficient, D -Diffusion Time, t -Physical time between gradients used to “tag” H 2 O -Size of Compartment(s) - If we set a limit for  r, then we observe an apparent diffusion coefficient, ADC -Tortuosity of the Compartments - More tortuous paths look like slow diffusion -Temperature -Viscosity *** We can only measure “ADC” because of all the factors that change “D”! *** B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

Steps in Performing DWI DWI (isotropic): –Collect a DWI (b = 1000 or 500 s/mm 2 ) dataset by applying motion probing gradients in the x, y, and z-direction. Make sure TE is low and TR is long to increase SNR For higher resolution scans, use a lower b-value –Collect a T2w dataset (b = 0 s/mm 2 ) –Collect a low b-value, flow nulled dataset (b = 50 s/mm 2 ) –Average DWIs from 3 directions –Calculate ADC B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 For b-values < 1000

DWI vs. ADC DWI –Images collected during application of a “diffusion sensitizing gradient” –Contains T1, T2, and ADC effects –“Restricted diffusion”, long T2, and short T1 all influence DWIs B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 b = 1000 From: Taouli, Radiology, 2010 b = 750

DWI vs. ADC DWI –Influence of T2 in DWIs is known as “T2 shine through” B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 From: Taouli, Radiology, 2010 b = 500 ADC Map

DWI vs. ADC ADC –Quantitative –Calculated from DWI and T2w (b = 0 or low b-value) B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 From: Taouli, Radiology, 2010

DWI vs. ADC ADC –Reflects diffusion magnitude –Eliminates long T2 and short T1 effects B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 From: Taouli, Radiology, 2010

DWI vs. ADC DWI –Influence of T2 in DWIs is known as “T2 shine through” B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 From: Taouli, Radiology, 2010 b = 500 ADC Map

Diffusion Tensor Imaging (DTI) Isotropic Diffusion Anisotropic Diffusion From: Ellingson, Concepts in MR, 2008 B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

Diffusion Tensor Imaging (DTI) B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Directional Encoding 6 directions (min)15 directions 25 directions41 directions

Diffusion Tensor Imaging (DTI) B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 The Diffusion Tensor:

Diffusion Tensor Imaging (DTI) B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Isotropic Diffusion 1 = 2 = 3 Anisotropic Diffusion 1 > 2, 3 From Ellingson, Concepts in MR, 2008

Fractional Anisotropy (FA) IsotropicAnisotropic FA = 0 FA = 1 B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

DTI Tractography In the CNS and MSK, lADC is parallel to axon orientation B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

DTI Tractography In the CNS, lADC is parallel to axon orientation B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

DTI Tractography In the MSK, lADC is parallel to muscle fiber orientation From: University of Rochester B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

DTI Tractography In the heart, lADC is also parallel to muscle fiber orientation From: University of Oxford B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 From: Eindhoven University of Technology

DTI Tractography Spinal Cord Injury B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 From Ellingson, Neurosurgery:Spine, 2010

Steps in Performing DTI DTI (6 directions): –Collect a DWI (b = 1000 or 500 s/mm 2 ) along 6 non-collinear directions –Collect a T2w dataset (b = 0 s/mm 2 ) –Calculate Diffusion Tensor: Calculate D in 6 different directions Set up the encoding matrix Define Tensors Solve Tensor Equations B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

Applications of Diffusion MRI in the Abdomen B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

Diffusion MR Imaging of the Liver B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010

Diffusion MR Imaging of the Liver B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Common pulse sequences –Single-shot spin-echo (SE) echoplanar with fat saturation With breathhold (20-30 seconds; sensitivity for lesion detection = 84.3% Parikh, 2008 ) –Need thicker slices (8-10 mm) for good SNR and good liver coverage Resp. gated (3-6 min; sensitivity for lesion detection = 93.7% Parikh, 2008 ) –Thinner slices can be used (5 mm) –Better image quality, SNR and ADC quantification Taouli, 2009

Diffusion MR Imaging of the Liver B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Common pulse sequences –Single-shot spin-echo (SE) echoplanar with fat saturation With breathhold (20-30 seconds; sensitivity for lesion detection = 84.3% Parikh, 2008 ) –Need thicker slices (8-10 mm) for good SNR and good liver coverage Resp. gated (3-6 min; sensitivity for lesion detection = 93.7% Parikh, 2008 ) –Thinner slices can be used (5 mm) –Better image quality, SNR and ADC quantification Taouli, 2009 Common b-values –b = 0 image (no diffusion weighting…essentially a “poor man’s” T2w image)

Diffusion MR Imaging of the Liver B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Common pulse sequences –Single-shot spin-echo (SE) echoplanar with fat saturation With breathhold (20-30 seconds; sensitivity for lesion detection = 84.3% Parikh, 2008 ) –Need thicker slices (8-10 mm) for good SNR and good liver coverage Resp. gated (3-6 min; sensitivity for lesion detection = 93.7% Parikh, 2008 ) –Thinner slices can be used (5 mm) –Better image quality, SNR and ADC quantification Taouli, 2009 Common b-values –b = 0 image (baseline with no diffusion weighting…essentially a “poor man’s” T2w image –Low b-value (b < 150 s/mm 2 ) “Flow Nulled” Nulls the intrahepatic vascular signal Allows for better detection of focal liver lesions (van den Bos, 2008; Parikh, 2008; Okada, 1998; Hussain, 2005) ~2% change in ADC

Diffusion MR Imaging of the Liver B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Common pulse sequences –Single-shot spin-echo (SE) echoplanar with fat saturation With breathhold (20-30 seconds; sensitivity for lesion detection = 84.3% Parikh, 2008 ) –Need thicker slices (8-10 mm) for good SNR and good liver coverage Resp. gated (3-6 min; sensitivity for lesion detection = 93.7% Parikh, 2008 ) –Thinner slices can be used (5 mm) –Better image quality, SNR and ADC quantification Taouli, 2009 Common b-values –b = 0 image (baseline with no diffusion weighting…essentially a “poor man’s” T2w image –Low b-value (b < 150 s/mm 2 ) “Flow Nulled” Nulls the intrahepatic vascular signal Allows for better detection of focal liver lesions (van den Bos, 2008; Parikh, 2008; Okada, 1998; Hussain, 2005) –High b-value (500 < b < 1000 s/mm 2 ) Useful for focal liver lesion characterization (Taouli, 2003; Kim, 1999)

Diffusion MR Imaging of the Liver B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Visual liver lesion characterization with DWI From: Taouli, Radiology, 2010

Diffusion MR Imaging of the Liver B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Visual liver lesion characterization with DWI From: Taouli, Radiology, 2010 b = 500ADC From: Xu, J Comput Assist Tomogr, 2010

Diffusion MR Imaging of the Liver B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Visual liver lesion characterization with DWI From: Xu, J Comput Assist Tomogr, DWI has higher specificity than CE

Diffusion MR Imaging of the Liver B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 From: Colagrande, Radiol Med, 2006 Cirrhotic Liver--  ADC Liver Cysts --  ADC Angioma--  ADC FNH--  ADC Hepatocarcimoma --  ADC (mixed results) Metastasis--  ADC (mixed results)

Diffusion MR Imaging of the Kidneys B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Directionality -- DTI?

Diffusion MR Imaging of the Kidneys B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Directionality -- DTI? From: Kido, Acta Radiol, 2010 Fractional Anisotropy (DTI)

Diffusion MR Imaging of the Kidneys B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 From: Colagrande, Radiol Med, 2006 b = 0 b = 500 ADC From: Kido, Acta Radiol, 2010 From: Kilickesmez, J Comput Assist Tomogr, 2009

Diffusion MR Imaging of the Kidneys B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Renal Fibrosis Animal Model -- From: Togao, Radiology, 2010

Diffusion MR Imaging of the Kidneys B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 Renal Cell Carcinoma From: Kilickesmez, J Comput Assist Tomogr, 2009 Contrast-Enhanced T1b = 1000ADC

Diffusion MR Imaging of the Kidneys B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010 From: Kilickesmez, J Comput Assist Tomogr, 2009

Summary Diffusion MRI is an MR technique that can quantify the magnitude of H 2 0 diffusivity within tissues –Microstructural information ADC calculated from diffusion MR images is influenced by: –Cellularity –Tissue viscosity and temperature –Diffusion Time –Compartment Size (cell size and shape) –Tortuosity of environment DTI is useful for directionality of diffusion restrictions –CNS, MSK, Kidney DWI/ADC maps can be used to characterize many pathologies of the abdomen –Liver and Kidney pathologies are most common abdominal diffusion MR studies B.M. Ellingson, Ph.D., Dept. of Radiological Sciences, David Geffen School of Medicine at UCLA, 2010