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HFO MRI By Bradley Blackburn, MD S INCE ITS CLINICAL introduction in the early 1980s, MRI has become progressively more utilized, and is now a mainstay of diagnostic medical imaging. As a tool in the radiology department, MR is not only indispensable for the neurosurgeon and orthopedic surgeon but also is becoming increasingly important for vascular and abdominal imaging. MR in some ways is uniquely suited to tissue character differentiation and is vastly more versatile than CT in terms of tissue plane analysis and ���manipulation��� of proton relaxation parameters to accentuate fat or water content and effectively characterize pathology. MR has two widely accepted configurations; the bore magnet and the planar, or open magnet. Tube or bore configurations are electromagnets and typically have magnetic field strength ranging from 1 to 3 tesla, and they require cryogen cooling. Most open magnets (all, until recently) are fixed magnets, and have field strength of 0.2 to 0.7 tesla and are air cooled. Open configuration magnets are uniquely suited to certain patient populations, including those that are obese or claustrophobic. They are reliable, but there also are definite limitations. Field strength is directly related to proton excitation and, therefore, directly to image quality. Certain body parts are more easily imaged than others, and the dictum has been that some diagnostic information is better than no information if a patient is unable or unwilling to be scanned in a conventional tube magnet. However, the criticism of open magnets, especially among sub-specialists, has always revolved around diagnostic image quality. This is especially apparent, for example, in axial plane C-spine work, where narrow coils are required, and with more difficult body parts to image, such as the shoulder, where epicenter is more difficult to achieve. Additionally, fat suppression is less reliable with lower field strengths, which is an irony since many of the patients requiring the modality are obese. Certain sequences, such as inversion recovery, are particularly vulnerable to lack of field strength but are an important part of the radiologist���s diagnostic regimen. All sequences are susceptible to patient motion, and low field magnets take longer to acquire information regardless of the tissue parameters set. Field of view also is another important factor if pathology is small enough to go undetected. Many of the issues outlined above have been solved with the introduction of planar configured electromagnets, so called High Field Open, or HFO. The physics is complex and beyond the scope of this article, but suffice it to say that HFOs with field strength of 1.0 tesla generate images of comparable diagnostic quality when compared with any standard tube magnet. These magnets also provide the programming sophistication necessary to get quality imaging of less typical body parts such as the breast, vascular structures, biliary tree and heart. Respiratory gated acquisition is improved due to so called ���turbo echo,��� ultrafast sequences obtained by manipulating ���flip angle��� capture. Flow related, non-contrast enhanced, 3-D imaging of the carotids, circle of Willis and even the renal arteries is markedly improved. All in all, HFOs provide a substantial change in the clinical paradigm of diagnostic medical imaging, and the improved quality should make these machines a welcome ���newcomer��� for most practitioners, especially surgical subspecialists. Dr. Bradley Blackburn is a boardcertified interventional radiologist on the Medical Staff at Southwest General. ��� JANUARY- FEBRUARY 2013 ��� MDNEWS.COM ��� MD News Cleveland/Akron/Canton | 21