In the Human Imaging Core, MRI is the most commonly used technique for determining total kidney volume, renal blood flow and cardiac analysis, though other methods are used as appropriate.
The Mayo Clinic Radiology Informatics Laboratory assists the Human Imaging Core in coordinating image measurement and analytics.
Analysis of kidney and liver volumes
Renal and liver volumes are obtained with coronal T2-weighted images. Nonenhanced 3-D, volume-interpolated, spoiled gradient-echo coronal T1-weighted images are obtained at 3 millimeters contiguous slice thickness.
Individual kidney volume is measured from the T1-weighted images using a stereologic method — Analyze software — and calculated from the set of contiguous images. A number of image measurement tools in the Radiology Informatics Laboratory complement these efforts.
Because registration and subtraction could likely also help identify regions of change in polycystic kidney disease, the Human Imaging Core has a developmental project underway to create a tool suitable for kidney-sized rigid and semirigid registration. This would allow for the definition of thresholds and the computation of the volume of change — usually for individual cysts — which could then be summed to create a global measurement.
Renal blood flow measurements
Magnetic resonance renal blood flow measurements can be obtained with thick-section, oblique-axial, 2-D, phase-contrast, breath-hold magnetic resonance angiograms along the course of each renal artery as reference images.
Magnetic resonance renal artery flow measurements are then obtained perpendicular to the oblique-axial, 2-D reference images of the renal arteries using a cardiac-gated, 2-D, fast gradient-echo, phase-contrast pulse sequence.
Flow analysis is performed using Flow software, while semiautomated techniques are used for definition of the vessel borders in the flow images.
Evaluation of cardiac function
MRI is recognized as the gold standard for quantification of ventricular volumes and function. Cardiac function, chamber size and left ventricular mass are determined from short-axis, electrocardiogram-gated, steady-state, free-precession cine images.
After initial localizing scans, two-chamber and four-chamber scout images are acquired and used to prescribe cine short-axis views extending from the base of the left ventricle to the apex. Epicardial and endocardial borders of the left ventricle are traced at end systole and end diastole using commercially available software.
Right ventricular volumes, ejection fraction and mass are measured in an identical manner.
For more information about image analysis services offered through the Human Imaging Core, contact the core.