Magnetic Particle Imaging in Medicine
Magnetic Particle Imaging (MPI) is a new imaging technology that answers a clinical need for a safe, rapid 3D angiography technique without ionizing radiation or toxic tracers to image intracranial diseases such as stenosis (stroke), aneurysm, vasospasms and malformations. The MPI tracer is made with super-paramagnetic iron oxide (SPIO), significantly safer than iodine (used in CT and fluoroscopy), and gadolinium (used in MRI). The safe tracer and absence of harmful radiation leads to reduced long-term medical costs for patient undergoing diagnostic angiography, and especially patients undergoing repeated diagnostic angiography procedures associated with long-term care.
| MPI | ECHO (US) | PET/ SPECT | MRI | CT | ||
|---|---|---|---|---|---|---|
| Emerging Applications in Clinical Imaging | Early Stage Inflammation | +++ | – | +/- | – | – |
| Vulnerable Plaques | +++ | – | +/- | – | – | |
| Screening/ Staging (Safe, non-ionizing) | +++ | +++ | – | +++ | +/- | |
| Current Methods | Functional (Perfusion, viability) | +++ | +++ | +++ | +++ | +/- |
Safe Quantitative Perfusion
MPI has the ability to quantitate blood flow from the major vessels to the capillary level giving a full perspective to potential cardiovascular disease.
Magnetic Particle Imaging in Perfusion and Angiography
Perfusion is a method of ensuring tissue health by measuring blood inflow and outflow at the capillary level. This is in contrast to angiography, which measures artery and vein diameter. Perfusion (and angiography) are typically performed by injecting a contrast agent or tracer agent and measuring the time dependent changes in a tomographic imaging device such as CT or MRI. Image processing is used to isolate the signal arising from the tracer from other signals, such as tissue. The isolated agent signal is then processed to estimate tissue parameters such as blood flow (CBF) and blood volume (CBV).
Magnetic Particle Imaging Perfusion
Computed Tomography Perfusion (Human)
The reliability of the perfusion imaging is limited by our ability to isolate the injected agent signal from other signals. After rapid (bolus) injection, CT perfusion and MPI perfusion take repeated scans to visualize signal changes due to the agent passing through tissue being imaged. Here we see that the signal changes in CT are subtle and are difficult to isolate from the bone and tissue signal, which severely impacts the reliability of the technique. In contrast, because MPI uses a tracer agent and does not see background tissue, the signal arising from the agent is clear and unambiguous. *Simulated data.
Perfusion: Vasculature in a Rat Head
MPI shows great promise for reliable perfusion imaging, and some of perfusion’s tissue parameters can be measured directly. One key parameter of perfusion, Blood Volume (shown here), can be measured directly because of MPI’s “perfect” tracer contrast. *In vivo animal data courtesy of UC Berkeley, Conolly et. al.
Exquisite Sensitivity
High Contrast for Clear Decisions
Since MPI directly detects a tracer and does not see tissue, it creates a “Positive Contrast” image. This means that when performing angiography, vasculature shows up bright against a black background.
MPI’s unambiguous identification of the tracer agent results in more reliable and easier to analyze data. Agent in-flow and out-flow is unambiguous and high-contrast, which should result in far more reliable estimation of perfusion parameters such as blood flow and blood volume. *Simulated data.
Addressing Safe Imaging for the 21st Century
Unlike CT, MRI and PET, Magnetic Particle Imaging does not require toxic contrast agents or use mutagenic radiation. MPI’s safety is driven by the use of a clinically approved SPIO nanoparticles, which have been proven safe for patients with weak or damaged kidneys. These nanometer-sized particles are easily broken down in the body and turned into hemoglobin. MPI perfectly supports long term diagnostic monitoring without cumulative radiation or toxicities.