03-09 The Right Choice
The traditional donut-shaped machines allow very high field strengths and thus are well suited for research applications and specific techniques such as BOLD imaging. Many of these machines are not very comfortable for patients and annoyingly, partly dangerously loud; the noise of gradient switching can sound like a jackhammer. During the last two decades machines with larger bores have been developed to lower the rate of claustrophobia and allow studies of obese patients.
Open systems reduce patient claustrophobia and are better suited for interventional purposes because there is access to the patient from all sides. Open systems are available between 0.3 T with permanent magnets to 1.5 T with superconducting magnets. Recent developments focus on machines between 0.5 and 1.2 T. They include equipment with MgB2 coils. Many open systems are quiet, offer more space for handicapped and large patients – and children.
Dedicated systems are aimed at, e.g., orthopedic imaging. Examinations of knees, elbows, hands, and shoulders are the main indications. These systems are smaller and easier to install.
The choice of an MR system might be quite agonizing and depending on hearsay, fashions, money, ego, character strength, and politics. Field strength is one, but not the only and most important, parameter; higher field strength does not necessarily guarantee a better quality system or better diagnostic outcome for the patient. Image quality can be worse; the intensity of artifacts scales with field strength. Beware of weasel words such as "increased diagnostic confidence score"; they are not objective measurements but sales jargon.
Needs must be carefully assessed in the choice of an MR machine. The quality of the component parts, both in terms of hardware and software, makes a considerable impact on the equipment. Service, maintenance, and knowledge of how to run the system are of pivotal importance for image quality and assessment.
When contemplating the purchase of an MR imaging machine thoughtful consideration must not only include price, service costs, and reimbursement structure, but also other aspects that are involved in the cost versus benefit calculation.
In the case of 1.5 Tesla versus 3.0 Tesla one should weigh the points in Table 03-04.
Some additional scientific and non-scientific aspects to be taken into account when deciding between 1.5 and 3.0 Tesla magnet systems. * [⇒ Pattany]