Open Vs. Closed MRI Magnets

The terms ​“closed” and ​“open” gen­er­al­ly refers to the geom­e­try of the mag­nets used in MRI scanners.

The ​“closed” mag­net con­fig­u­ra­tion refers to a tube-like tun­nel which was the orig­i­nal shape of most MRI scan­ners. All high-field super­con­duct­ing MRI scan­ners (1.0 to 3 Tes­la-Tes­la being a mea­sure of the strength of the mag­net­ic field) are gen­er­al­ly con­sid­ered a part of this type.

Open mag­nets were devel­oped in the 1990’s, and typ­i­cal­ly con­sist of two large, round, hor­i­zon­tal­ly ori­ent­ed met­al discs which are the poles of the mag­net with the patient lying on a table between the poles. These mag­nets have no sides and are thus ​“open”. ​“Open” mag­nets have a mag­net­ic field strength of 0.2 to 0.3 Tesla.

In both ​“closed” and ​“open” mag­nets, there are dif­fer­ences and trade-offs. Extreme­ly claus­tro­pho­bic patients often pre­fer an ​“open” MRI envi­ron­ment. Pre­vi­ous­ly, larg­er patients could only fit in ​“open” MRI scan­ners. ​“Closed” MRI scan­ners typ­i­cal­ly scan patients faster than ​“open” MRI scan­ners. In addi­tion, ​“closed” MRI scan­ners with high field strengths are capa­ble of achiev­ing greater res­o­lu­tion and thin­ner slices for view­ing small­er parts of a patien­t’s anato­my and offer a more pre­cise diag­no­sis. Advanced tech­niques to detect ear­ly stroke, sub­tle mul­ti­ple scle­ro­sis plaques and car­ti­lage degen­er­a­tion in the knee are avail­able only on high-field ​“closed” scan­ners, as well as the abil­i­ty to per­form spe­cial­ized exams such as breast and prostate MRIs.

Patients should be aware of the dif­fer­ences in qual­i­ty and scan­ning time and the poten­tial that anoth­er scan might be required by their physi­cian if an exam is acquired with a tra­di­tion­al ​“open” scan­ner. Due to the low­er image qual­i­ty pro­duced by the ​“open” scan­ners because of the low­er field strength mag­net, an exam may need to be repeat­ed on a ​“closed” or high-field scan­ner to accu­rate­ly diag­nose the patien­t’s prob­lem. This results in patient incon­ve­nience as well as addi­tion­al cost for a sec­ond scan.

For a while, there was an increase in use of ​“open” MRI’s due to the ​“closed” scan­ners being more claus­tro­pho­bic for patients. New­er scan­ners have since been designed with a sub­stan­tial­ly short­er bore or ​“tube” than the old­er scan­ners to increase patient com­fort and reduce patient anx­i­ety. These mag­nets are flared at the ends and wider than the old­er scan­ners reduc­ing that ​“closed in” feeling.

DMG has three scan­ners of this design uti­liz­ing a 60cm bore. We have also recent­ly added three addi­tion­al scan­ners with the widest avail­able bore open­ing avail­able for med­ical imag­ing. These mea­sure 70cm in diam­e­ter with a patient weight lim­it of 500 – 550 lbs., enhanc­ing the ​“open” con­cept and mak­ing it pos­si­ble for patients who have nev­er been able to be scanned before to lie inside com­fort­ably. These short bore mag­nets are also designed with supe­ri­or ven­ti­la­tion and light­ing sys­tems, allow­ing more light and air to cir­cu­late around the patient dur­ing scanning.

In addi­tion to the phys­i­cal struc­ture of the scan­ners reduc­ing patient anx­i­ety, DMG’s MRI tech­nol­o­gists and sup­port staff are expe­ri­enced in deal­ing with patients who may be ner­vous or anx­ious. Our staff can com­fort and relax patients, talk them through the scan and, if need­ed, sit with the patient and hold their hand. Music can some­times be lis­tened to dur­ing a scan for relax­ation purposes.

I just had an MRI last month on an ​“open” scan­ner because I’m claus­tro­pho­bic. Now my doc­tor wants the exam repeat­ed on a high-field mag­net. What does that mean?

“Open” mag­nets have a mag­net­ic field strength of 0.2 to 0.3 Tes­la while high-field super­con­duct­ing MRI scan­ners have a mag­net­ic field strength of 1.0 to 3T (or Tes­la-Tes­la being a mea­sure of the strength of the mag­net­ic field). These high-field mag­nets are capa­ble of achiev­ing greater res­o­lu­tion and thin­ner slices for view­ing small­er parts of a patien­t’s anato­my, offer­ing a more pre­cise diag­no­sis. Most advanced tech­niques and exams are avail­able only on high field scan­ners. New­er scan­ners have been designed with a sub­stan­tial­ly short­er bore or ​“tube” than the old­er scan­ners to increase patient com­fort and reduce patient anx­i­ety. These mag­nets are flared at the ends and wider than the old­er scan­ners reduc­ing that ​“closed in” feel­ing. These short bore mag­nets are also designed with supe­ri­or ven­ti­la­tion and light­ing sys­tems, allow­ing more light and air to cir­cu­late around the patient dur­ing scanning.

Due to the low­er image qual­i­ty pro­duced by the ​“open” scan­ners because of the low field mag­net, an exam may need to be repeat­ed on a ​“closed” or high field scan­ner to accu­rate­ly diag­nose the patien­t’s prob­lem or increase the physi­cian’s abil­i­ty to treat a patient when an ​“open” scan does­n’t show suf­fi­cient information.