As the saying goes, “a picture is worth a thousand words.” However, when it comes to medical imaging, a picture can be worth two, or even sometimes three thousand words. In fact, it is difficult to even imagine modern health care without any imaging whatsoever. Aside from non-invasively diagnosing a patient, imaging plays a key role in determining treatment efficacy. Over the years, several types of imaging have been developed, each one as unique as the other.
All of the major imaging modalities on the market today have their advantages. Nuclear imaging, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT) offer great functional information in terms of drug quantification and assessing its biodistribution. Computed tomography (CT), also known as a CAT scan, remains the quickest modality and the go-to imaging choice of many emergency situations. Ultrasound (US) remains the cheapest as well as the easiest imaging modality to use and transport; in fact US transducers can now be plugged into any laptop or smartphone. Of them all, magnetic resonance imaging (MRI) provides the best soft tissue contrast.
The Most Complex of all Imaging Modalities
When compared to the other modalities, MRI’s main advantage remains the benefit of not using any ionizing radiation such as with PET, SPECT and CT. MRI relies on forming an image from the signal acquired from spinning hydrogen atoms located on water molecules within the human body. Although US does not use any ionizing radiation either, its use remains fairly limited due to results being very operator dependent.
However, despite these advantages, MRIs remain the most complex of all imaging modalities. Contraindications, such as pacemakers as well as certain surgical implants, limit patient participation. Moreover, claustrophobia, loud noises, and lengthy imaging times (all relative to the other modalities) remain a persistent complaint from patients.
Nevertheless, what makes MRIs so complex is the intricacy of the scan parameters. Depending on the pulse sequences used, different types of images can be acquired:
- Functional MRI (fMRI) allows for the assessment of minor fluctuations in oxygen consumption by different tissues
- Diffusion-tensor-imaging (DTI) enables the diffusion of water molecules to be imaged along neuronal axons
- Magnetic resonance spectroscopy (MRS) permits the quantification of metabolic changes taking place within specific tissue regions
This is all to name a few.
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7T – A Magnetic Field Much Stronger than that of the Earth
MRIs are designated by the strength of the magnetic field they create (measured in Tesla, T) and at the moment, most clinical sites only have an MRI with 1.5T or 3T capabilities. Nonetheless, in late 2017, the Siemens MAGNETOM Terra 7T scanner was approved by the Food and Drug Administration (FDA) for clinical use. With a magnetic field 140,000 times more powerful than that of the Earth, the 7T offers the best imaging resolution possible.
Signal-to-noise ratio (SNR) is directly proportional to the strength of magnetic field (B0), and the 7T allows for an even better patient assessment. Diseases oftentimes manifest themselves via microscopic structural and anatomical changes prior to patients displaying any clinically significant symptoms. This means that patients may now benefit from a possible earlier diagnosis, which would result in treatment administration at a less severe disease state and thus hopefully improve patient outcome.
The greatest benefit of the 7T MRI is anticipated within the field of neurology, for assessment and detection of diseases such as Alzheimer’s and multiple sclerosis (MS). However, the increased resolution could be of benefit in the treatment of any medical complication.
Standardization Remains Key
Imaging has become a huge part of clinical trials, playing a key role when it comes to the patient’s original clinical diagnosis, participant screening for trial eligibility, monitoring of disease progression at various time points, and ultimately determining treatment efficacy as well as disease status. With imaging becoming a major endpoint within certain trials, it simply cries out for the use of more accurate and powerful machines such as the 7T. However, the 7T’s implementation within the clinical trial industry could prove challenging.
The cost of the machine remains the biggest issue with the rule of thumb being roughly $1 million per Tesla, $7 million in this case. The 7T’s implementation seems a little far reaching when considering that clinical trials already make up the majority of the cost behind most approved bio-pharmaceutical products. Higher drug prices oftentimes reflect greater spending during clinical trials, among many other factors. Use of an even more powerful machine would only increase the overall price tag of drugs once they reach the market.
In addition, with such a heavy affiliated price tag, the outsourcing of clinical trials could be compromised. Clinical trial sites within third world countries may not have the needed resources to house and maintain a 7T. Although MRIs acquired from different manufacturers may not be a significant issue, using MRIs with different field strengths could impact the study end results. Standardization remains key.
7T Will Improve Accuracy of Patient Assessment
Moreover, patient comfort and safety is of great importance when conducting clinical trials. With such a strong magnetic field, physiological effects such as dizziness and vertigo are much more common than with 1.5T or 3T machines. Knowledge of such effects warrants clinical trial staff to increase patient monitoring post-imaging. Furthermore, higher noise levels and greater chances of peripheral nerve stimulation could impact overall patient satisfaction.
Despite all of the aforementioned limitations, the 7T remains a robust and powerful machine, with unprecedented capabilities. As we learn more about some of its possibilities, its implementation will become much more common, and the accuracy of patient assessment and clinical endpoints much more prominent.
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- Nishimura, D. (2010). Principles of Magnetic Resonance Imaging (Edition 1.2). Raleigh, NC: Lulu Press.
- Siemens Healthineers (2018). Translate 7T Research Power Into Clinical Care with MAGNETOM Terra.