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Questions and Answers
What phenomenon allows T2 Shine Through to occur in certain tissues?
What is the primary advantage of the RESOLVE DWI technique?
Which of the following imaging applications is NOT mentioned for DWI?
What does a low ADC value indicate in liver imaging?
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Which technique is commonly used for MRI perfusion that relies on susceptibility-induced signal loss?
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Which advanced technique specifically narrows the field of view to target particular regions for high-resolution imaging?
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Which of the following is a clinical application of PWI?
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What is one common clinical application of DWI?
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What does increased mean transit time (MTT) in the right hemisphere indicate?
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Which feature of perfusion-weighted imaging (PWI) helps differentiate high-grade tumors from normal brain tissue?
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What does a low relative cerebral blood volume (rCBV) suggest in the context of a mass surrounding the lateral ventricle?
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What characteristic of blood vessels in tumors as compared to normal brain tissue is utilized in PWI?
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In what way does the ADC value in more solid anteromedial parts compare to normal brain tissue?
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What is the purpose of administering a dose of 0.2 mm/kg of Gd intravenously during the DSC technique?
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Which parameter measures the time it takes for fresh blood to completely replace blood within a volume of interest?
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In DCE-MRI, what type of images are used to measure signal changes caused by the paramagnetic tracer?
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What is the main advantage of using Arterial Spin Labeling (ASL) in imaging?
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How is the Time to Peak (TTP) calculated and what does it represent?
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Why is DSC used in patients with acute ischemic stroke?
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What type of software is used to convert raw data images in DSC into more interpretable formats?
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What is a crucial factor that Arterial Spin Labeling (ASL) uses to track blood flow in tissue?
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What does a higher b-value in diffusion-weighted imaging indicate?
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What is the primary purpose of the ADC map in diffusion MRI?
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In which scenario would you expect to see low ADC values on the ADC map?
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What does the term 'T2 shine through' refer to in diffusion-weighted imaging?
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What characteristic do high ADC value areas typically exhibit on the ADC map?
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What is the effect of increasing the b-value on diffusion weighted imaging signals?
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What is the role of Brownian motion in diffusion MRI?
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How does the ADC map help in clinical studies regarding tissue conditions?
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Study Notes
Diffusion Weighted Imaging (DWI)
- DWI measures the mobility of water protons, providing insights into tissue microstructure
- Diffusion relies on the incoherent thermal motion of water molecules (Brownian motion)
- b-value reflects the strength and timing of gradients used to generate DWI images, expressed in sec/mm2
- Higher b-value increases diffusion weighting, leading to signal attenuation
- b0 produces T2 imaging
- b1000 produces more strongly diffusion weighted images
- b3000 produces very high diffusion weighted images with lower signal-to-noise ratio (SNR)
Apparent Diffusion Coefficient (ADC) Map
- Calculated using at least two diffusion-weighted images with different diffusion sensitivities
- Shows the strength of diffusion
- Reversed contrast compared to DWI images
- Eliminates T2 contrast in DWI imaging
- Eliminates common artifacts
ADC Map Interpretation
- High ADC Values: Areas with high water diffusion, such as fluids or areas with fewer cellular structures (e.g., cerebrospinal fluid, cysts)
- Low ADC Values: Tissues with restricted water diffusion due to increased cellularity or compactness (e.g., strokes, tumors, inflammation, cellular proliferation)
T2 Shine Through
- High signal in DWI not due to restricted diffusion but due to high T2 signal "shining through"
- Occurs due to long T2 decay time in some normal tissues
Advanced DWI Techniques
- RESOLVE DWI: Provides high-resolution DWI with reduced susceptibility-related artifacts, especially in regions prone to artifacts
- ZOOMit DWI: Provides high-resolution DWI of specific regions of interest, minimizing susceptibility artifacts by focusing field of view on targeted areas
DWI Clinical Applications
- Whole-body cancer screening
- Brain imaging
- Prostate imaging
- Gynecology imaging
- Breast imaging
- Anterior neck imaging
- Small bowel imaging
- Liver imaging
- Spine imaging
- Sacroiliac joint imaging
DWI Case Examples
- Differentiating Chronic, Acute, and Subacute Infarcts
- Brain Tumors
- Liver (low ADC indicates active lesion)
- Prostate
- Bone Metastasis
- Whole-Body DWI (Lymphoma screening, Metastases screening, Treatment monitoring, Follow-up, used as an alternative to PET)
Perfusion Weighted Imaging (PWI)
- Measures blood delivery at the capillary level in units of milliliters per 100 grams per minute
- Closely related to oxygen and nutrient delivery to tissues
- Used for imaging: Stroke, Brain Tumors, Dementia, Psychiatric Illnesses, Trauma, Epilepsy, Multiple Sclerosis
PWI Techniques
-
Dynamic Susceptibility Contrast (DSC):
- Uses gadolinium-based contrast and T2*-weighted sequences to measure blood flow
- IV injection of 0.2 mmol/kg of gadolinium
- Fast T2*-weighted EPI sequences capture the first pass of contrast through microcirculation
- Raw data images converted into maps (CBV, CBF, TTP, MTT)
-
Dynamic Contrast Enhanced Imaging (DCE-MRI):
- Uses rapid, repeated T1-weighted images to measure contrast agent diffusion
- IV injection of contrast agent
- Contrast agent diffuses from blood into the extravascular space
-
Arterial Spin Labeling (ASL):
- Non-invasive, non-ionizing
- Magnetically labels arterial blood water protons as an endogenous tracer
- Measures cerebral blood flow (CBF)
- Suitable for pediatrics, patients with impaired renal function, and serial follow-up
Clinical Cases of PWI
- Acute Ischemic Stroke: Depicts perfusion deficits to aid in diagnosis and treatment planning
- Brain Tumors: Predicts tumor type and grade, patient survival, and optimal therapeutic options; differentiates post-treatment radiation necrosis from recurrent tumor
PWI for Brain Tumor Characterization
- Exploits tumor vasculature characteristics
- Higher blood vessel density in tumors than normal brain tissue
- High-grade tumors have higher blood volume
- Increased CBV and CBF in tumors compared to normal tissue
- Higher MTT in tumors
- Differentiates tumors from radiation necrosis (hypo-perfused, low CBV, CBF, and MTT)
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Description
Explore the principles of Diffusion Weighted Imaging (DWI) and Apparent Diffusion Coefficient (ADC) maps. This quiz covers the technical aspects, including b-values, and interpretation of ADC in assessing tissue microstructures. Enhance your understanding of water mobility and its implications in medical imaging.
