Feature article

MRI bore sizes and benefits

Traditionally, MRI scanners have had a 60 cm (23.6 in.) bore. Because of this, many patients reported claustrophobia. Others were unable to have an MRI scan, because they could not fit inside the bore. In order to accommodate these patients, some companies began to use open-bore MRI scanners, which sacrificed image quality for patient comfort. Within the last decade, MRI manufacturers have begun producing wide bore MRI scanners. These wide bore scanners have a 70 cm. bore. 70 cm. is roughly 27.6 in. and just over two feet. Both wide and narrow bores can have 1.5T or 3.0T magnet strengths.

The importance of the bore

MR scanners are shaped similarly to donuts. The open space in the middle where a donut hole would go is what the MR community refers to as the bore.1 The area surrounding the bore contains the magnet, so the size of the bore is related to the size of the magnet. Therefore, longer or wider bores contain longer or wider magnets. Patients lay on the patient platform, also called the patient table, and are then positioned by the technologist within the scanner. This part of the scan can cause claustrophobia in some patients with a closed-bore scanner.

The benefits of closed bore MRI

Closed bore MRI allows for the scanner to acquire detailed pictures.2 The doctors are more likely to accurately read the images and diagnose and treat the patient more accurately. The increased sensitivity of these traditional scanners is largely due to the decreased size of the magnetic field. The magnet is therefore more concentrated and sends out stronger signals for the computer to process. The magnet also encompasses the body, permitting imaging of some body parts that may not be able to be scanned by an open bore machine.

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The benefits of wide bore MRI

The wide bore MRI scanner is a play on the traditional closed bore scanner. The magnet encompasses the body, like the narrower scanners. Likewise, there are many benefits associated with a wide bore scanner, including increased image quality and increased patient comfort.

Although some of the image quality is lost between a narrow and wide bore scanner, wide bore scanners still provide better images than their open bore counterparts. This is because open MR scanners use a significantly weaker magnet. In fact, the typical open MR scanner has a magnet strength of 0.3T to 0.7T.3 Closed bore scanners are typically 1.5T or 3.0T. High magnet strengths improve image quality due to the increased signal strength. This is measured in the signal-to-noise ratio (SNR). Higher SNR means higher detail images.

In terms of comfort, the wide bore scanners surpass both the narrow bore and the open bore scanners due to increased space and shorter scan times.4,5,6 Wide bore scanners have a bore diameter of 70 cm. This is 10 cm more than narrow bore (60 cm). Additionally, open bore scanners have roughly 40-45 cm head space, which is almost a foot less room than wide bore scanners. Claustrophobic patients may have less trouble with wide bore MRI. The increased space goes around the patient in respect to a narrow bore. This not only accommodates the claustrophobic but also helps large stature and obese patients. Likewise, wide bore scanners can hold up to 550 lbs (249.5 kgs). Finally, closed MRI can be up to twice as fast as open MRI, meaning that the patient doesn't have to stay still or be in the exam room for anywhere near as long.7

The images produced by a closed and wide bore scanners could help doctors to more accurately diagnose a person's illness due to the increased image quality. With wide bore scanners, patients who may have felt claustrophobic in a standard 60 cm scanner may be more comfortable in the wider bore. Additionally, patients who could not fit inside a narrow bore may be able to lay comfortably with the extra space a wide bore provides thus increasing the number of patients that can be scanned.

References

1. Todd A. Gould, RT-(R)(MR)(ARRT) and Molly Edmonds. "How MRI Works." HowStuffWorks.com. 25 October 2010. Web. 20 December 2018. <https://science.howstuffworks.com/mri.htm>.

2. "Open MRI vs Closed MRI: What is the Difference and Which One is Best Suited for You?" IndependentImaging.com. Web. 28 December 2018. <https://www.independentimaging.com/open-mri-vs-closed-mri-difference-one-best-suited/>.

3. DuPage Medical Group Radiology. "4 Benefits of Wide Bore MRI Systems." DuPageMedicalGroup.com. Web. 20 December 2018. <https://www.dupagemedicalgroup.com/health-topics/post/4-benefits-of-wide-bore-mri-systems/>.

4. Wlad T. Sobol. "Recent advances in MRI technology: implications for image quality and patient safety." Saudi J Ophthalmol. October 2012; 26(4): 393-399. Web. 20 December 2018. <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3729307/>.

5. "Technology meets comfort with Wide Bore MRI." Ochsner.org. Web. 20 December 2018. <https://www.dupagemedicalgroup.com/health-topics/post/4-benefits-of-wide-bore-mri-systems/>.

6. "Comfort and quality without the anxiety." Aurora.org. Web. 20 December 2018. <https://iconnect.aurora.org/ahcweb3/slmcrad/MR/Documents/Wide%20Bore%20MRI.pdf>.

7. Irene Maher. "More soothing MRI option is a tradeoff." Tampa Bay Times. 6 February 2013. Web. 20 December 2018. <https://www.tampabay.com/news/health/medicine/more-soothing-mri-option-is-a-tradeoff/1274118>.