What is the protocol for an MRI perfusion study?

MRI Perfusion Study Protocol

The standard MRI perfusion study protocol includes T2-weighted or fluid-attenuated inversion recovery (FLAIR) sequence, diffusion-weighted sequence (DWI), and perfusion-weighted sequence, typically using dynamic susceptibility contrast-enhanced (DSC) T2/T2-weighted MRI with gadolinium-based contrast agent.* 1

Core Components of MRI Perfusion Protocol

Pre-Contrast Sequences

• T2-weighted or FLAIR sequence to provide anatomical information and identify pathology 1
• Diffusion-weighted imaging (DWI) to detect cytotoxic edema and assess tissue status 1
• 3D MR angiography (MRA) of the circle of Willis, either without contrast (time of flight) or with contrast agent 1

Perfusion Sequence

• Dynamic susceptibility contrast-enhanced (DSC) T2/T2*-weighted MRI is the most common technique 1
• Requires rapid acquisition of images as a bolus of gadolinium-based contrast agent passes through brain vasculature 2
• Typically uses a single dose (0.1 mmol/kg) of gadolinium-based contrast agent 3
• Images must be acquired quickly enough to capture the first pass of the contrast bolus 1

Post-Processing Parameters

• Cerebral blood volume (CBV): Total volume of blood in a given region 1
• Cerebral blood flow (CBF): Volume of blood passing through a given region per unit time 1
• Mean transit time (MTT): Average time for blood to pass through the microvasculature 1
• Time to peak (TTP): Time from contrast injection to maximum contrast concentration 1

Technical Considerations

Contrast Agent Administration

• Gadolinium-based contrast agent is injected as a rapid bolus 3, 2
• For DSC perfusion, a compact bolus is needed for accurate measurements 2
• If contrast-enhanced MRA is performed, care should be taken to acquire data in the arterial phase to prevent venous opacification 1

Image Acquisition Parameters

• Echo-planar imaging (EPI) should be used when available 1
• In case of significant patient motion, radial acquisition schemes may be used (BLADE, PROPELLER, MultiVane, etc.) 1
• Recommended slice thickness: 3mm with no interslice gap at 3T; up to 4mm with no interslice gap at 1.5T 1

Clinical Applications

Acute Stroke Assessment

• Perfusion MRI can identify ischemic penumbra (potentially salvageable tissue) 1
• Perfusion/diffusion mismatch pattern indicates tissue at risk but potentially salvageable 1
• Typical pattern of collateral flow: lower peak, delayed TTP, increased MTT, decreased flow, normal or elevated CBF 1
• Typical pattern of absent collateral flow: decreased CBV (poor prognosis) 1

Brain Tumor Evaluation

• Standardized Brain Tumor Imaging Protocol (BTIP) includes DSC perfusion parameters 1
• Useful for differentiating tumor progression from pseudoprogression 1
• DSC-MRI has demonstrated 90% sensitivity and 88% specificity in differentiating true progression from pseudoprogression 1

Common Pitfalls and Limitations

• Lengthy examination time (30-45 minutes) can be challenging for acutely ill patients, though stroke-specific protocols can reduce this to 15-20 minutes 1
• Closed MRI environment makes patient monitoring difficult 1
• Quantification of DSC imaging requires robust determination of arterial input function (AIF) 1
• No standardization between MR machines, even of the same field strength, limiting comparison of objective parameters between sites 1
• Bevacizumab therapy affects DSC-MRI-derived rCBV values, which must be considered in patients undergoing this treatment 1
• Gadolinium-based contrast agents should be avoided in patients with advanced renal failure (estimated glomerular filtration rate <30 mL/min/1.73 m²) due to risk of nephrogenic systemic fibrosis 1