Source: www.medpagetoday.com
Author: Charles Bankhead, Staff Writer

Oral cancer’s spread to the mandible could not hide from a type of MRI that may facilitate more accurate staging and surgical planning, data from laboratory studies suggest.

Sweep imaging with Fourier transform (SWIFT) provided fine-detail views of cortical and medullary bone specimens, and the images exhibited good correlation with histopathologic findings.

The in-vitro studies did not specifically examine SWIFT’s ability to identify early cortical bone invasion by oral cancer. However, the high-quality images obtained from the investigation provide reason for optimism, the researchers reported in the September issue of Archives of Otolaryngology Head and Neck Surgery.

“Our study is very promising in that it offers a SWIFT-based MRI technique for accurate assessment of minute changes of cortical and medullary bone in three dimensions without any ionizing radiation,” Ayse Tuba Karagulle Kendi, MD, of the University of Minnesota in Minneapolis, and co-authors wrote.

“It has the potential to precisely determine the extent of mandibular bone invasion associated with oral carcinoma. This study is a crucial step toward the goal of developing a robust and noninvasive approach for preoperative imaging of mandibular invasion,” they added.

Carcinoma of the oral cavity often spreads to the mandible, but in many instances does not cross the periosteal layer, obviating the need for mandibulectomy. Limitations of current imaging techniques often preclude determination of bone invasion prior to surgery, the authors noted.

MRI and CT have been used most often to evaluate mandibular invasion of oral cancer, but conventional protocols in both modalities have drawbacks that often lead to unsatisfactory images.

The development of SWIFT has created new opportunities for more accurate preoperative assessment of the mandible in patients with carcinoma of the oral cavity, the authors continued. Employing time-shared excitation and signal acquisition, SWIFT allows detection of signals with a broad range of relaxation times, facilitating finely delineated evaluation of cortical and medullary bone.

The principal advantage of SWIFT involves to its protocol of near-simultaneous excitation and acquisition.

“SWIFT obtains signal from cortical bone that has a fast-decaying signal, produces less distortion from magnetic susceptibility, and is less sensitive to motion artifacts,” Kendi and colleagues wrote.

To assess the feasibility of SWIFT to detect bone invasion by oral cancer, the authors examined two mandibular specimens obtained from segmental resections. Imaging was performed by means of a 9.4-T, 31-cm horizontal MRI scanner, using a home-built, single-loop, 25-mm coil.

The SWIFT sequence involved excitation bandwidth and acquisition spectral width of 125 kHz, repetition time of 2.5 milliseconds, and 128,000 projections. Acquisition time averaged about eight minutes.

“SWIFT images of the specimens revealed detailed bone and soft-tissue anatomy, including soft-tissue tumor, cortical bone, and medullary bone,” the authors wrote in describing the images they obtained. “SWIFT demonstrated fine anatomic details, including nutrient vessels and fine trabecular bone structure.”

“SWIFT produced evidence of cortical bone invasion as cortical interruption of the hypointense signal of cortical bone. Medullary bone invasion was also demonstrated in both specimens as extension of soft-tissue tumor into the medullary cavity and replacement of medullary fat with tumor,” they said.

SWIFT imaging provided finely detailed images of the demarcation between tumor-free medullary bone and tumor invasion, they added.

“The correlations between the histologic and MR images of these two specimens clearly show malignant invasion that has not been previously demonstrated with MR techniques,” Kendi and colleagues wrote in their discussion of the findings. “The data described in this report suggest that [SWIFT] MRI has a great deal of potential in accurately determining bone invasion preoperatively.”

Note:
1. Co-authors Djaudat S. Idiyatullin and Michael Garwood disclosed relationships with Steady State Imaging.
2. Idiyatullin, Garwood, and co-author Curtis A. Corum disclosed royalty interests in products related to the research described in the article.

Source: Archives of Otolaryngology Head and Neck Surgery, Kendi ATK, et al “Transformation in mandibular imaging with sweep imaging with Fourier transform magnetic resonance imaging” Arch Otolaryngol Head Neck Surg 2