MR Spectroscopy

MR Spectroscopy

Conventional magnetic resonance (MR) imaging measures signals emitted by hydrogen nuclei from small voxels that have been selected by spatial variations in frequency and phase.

In addition to the detailed anatomical images provided through MR — including organs, soft tissues, bone and virtually all other internal body structures —two molecular MR technologies provide additional information on biochemical activity: MR spectroscopy (MRS) and MR with contrast agents.

MR Spectroscopy

MRS can extract information regarding the concentration of chemical compounds inside the body.  MRS is used to measure metabolites such as choline-containing compounds, creatine, inositol, glucose, N-acetyl aspartate and alanine and lactate, as well as drugs such as chemotherapeutic agents. MRS can generate and present data in two ways, including:

• a plot representing the chemical composition of a selected volume of tissue
• images that represent the concentration of a compound within the body.

Clinical Applications

Although MRS is primarily used in research, it has the potential to provide useful clinical information helpful in the diagnosis and treatment of disease, including:

• Metabolic disorders, especially those affecting the brain
  • MRS offers the ability to noninvasively assess neurochemical changes
  • MRS studies inform decision-making in neurotherapeutics
• Cancer
  • MRS provides information on tumor metabolism
  • Prostate
  • MRS can pinpoint the precise location of the cancer and help distinguish between clinically significant and insignificant prostate cancer
  • Breast
  • As an adjunct to MRI, MRS can reduce the number of false-positive results and invasive biopsies. MR imaging of the breast as a high rate of sensitivity (94-100%) for detecting tumors but a variable rate of specificity (37-97%) for distinguishing malignant from benign tumors. MRS is better able to distinguish malignant from benign tissue than MRI of the breast
  • Brain
  • Brain spectra (generated by measuring the levels of choline, creatine and N-acetylaspartate) can help physicians differentiate between recurrent tumors and changes due to radiation treatments
  • MRS allows for the precise targeting of radiation to recurrent brain tumors.

Advantages

• in the clinical setting, MRS adds seven to 10 minutes to the MR procedure
• MRS poses no known health risks.

Research

As research tool, MRS has provided important insights into disease, improving our understanding of the biochemistry of some disease states.

MRS is currently being used to investigate a number of diseases, including cancer of the brain, breast and prostate, epilepsy, Alzheimer’s Disease, Parkinson’s disease and Huntington’s Chorea, diabetes, and certain inflammatory and ischemic diseases.

MR with molecular contrast agents

Molecular, or targeted, MR uses iron oxide contrast agents that consist of suspended colloids of iron oxide nanoparticles. Such agents reduce the native T2 relaxation times within tissues where they are localized.   In addition to cellular imaging for the detection of disease and abnormalities and for monitoring treatment response, MR with molecular contrast agents may also be used therapeutically for drug delivery.

Agents used include:

• MION (Monocrystalline iron oxide nanocompounds)
• SPIO (Superparamagnetic iron oxide)
• Ultrasmall SPIO

Clinical Applications

• MR angiography
• lymphography
• tumor detection
• detection of infarctioned tissue
• liver tumor enhancement
• biomarker for the early detection, prognosis and assessing response to drug therapy for renal dysfunction
• gene transfection
• cell tracking
• immune cell trafficking
• cancer vaccines
• stem cell migration
• drug delivery.

Advantages

• high spatial resolution
• ability to extract physiologic and anatomic information simultaneously
• SPIOs provide the most change in signal per unit of metal
• MR molecular contrast agents are biocompatible, non-toxic and easily cleared from the organism and easily labeled.

Research

Primarily animal research but human clinical trials are expected within the next five years.

Clinical trials using MR cell tracking have been published and others are underway.

On the Horizon

Fusion Imaging

Combined MR/PET scanners will offer the ability to combine PET radiotracer studies with structural MR imaging, and either MR spectroscopy or MR with MR contrast agents with PET and MRI data being correlated both spatially and temporally.