MRI has advanced leaps and bounds over the past decade. New software and hardware developments allow us to visualize sensitive structures in the brain with higher clarity and resolution. This is especially helpful to identify subtle injuries and lesions that might otherwise be missed with standard MRI.
Unfortunately, many neurologists and even radiologists are not familiar with these modern techniques available for diagnosis. This is most apparent when managing patients who have sustained a traumatic brain injury.
Standard MRI sequences are great for structural abnormalities that can be visually evaluated but lack quantitative analysis of disease or injury. This is where Diffusion Tensor Imaging offers a wealth of information that conventional MRI is unable to provide.
Quantitative and Qualitative Imaging
MRI has many tools in the proverbial imaging “tool-box” to assess for various pathologic processes. For example, the T2 Flair sequence identifies multiple sclerosis lesions, while a susceptibility-weighted sequence identifies blood products. These sequences are referred to as qualitative imaging. Qualitative refers to imaging methods that are evaluated by a radiologist strictly by what they see. Whatever is visualized is what is reported on. The vast majority of MRI is performed using qualitative imaging.
Quantitative imaging provides measurable information from which to diagnose or compare. Unfortunately, modern quantitative imaging methods are frequently ignored in favor of qualitative imaging. Although qualitative imaging methods are satisfactory 95% of the time, subtle pathology may only be found by utilizing quantitative tools.
Types of Brain Injuries
Brain injuries are classified into one of two groups: focal or diffuse. Focal injuries are localized injuries caused by trauma and hemorrhagic or thrombolytic strokes. These injuries typically affect a limited region of the brain and are easily seen using a standard MRI imaging technique termed DWI (Diffusion-Weighted Imaging). DWI sequences reveal areas of “restricted diffusion”.
Water molecules travel in what is referred to as Brownian motion throughout the brain. This is the natural movement while taking into consideration the thermal properties of various types of tissue. Healthy tissue promotes the natural “free” motion of water molecules along the neural tracts of the brain. When a focal injury is sustained, the diffusion of water molecules is restricted in that area. Restricted diffusion is fairly easy to see using qualitative imaging techniques.
Diffuse brain injuries are those injuries that affect the brain in a scattered or “global” pattern. These injuries typically affect large portions of the brain but on a smaller scale of acuity. Injuries to the white matter tracts of the brain are frequently involved which can cause long term neurological deficits to patients who sustain these injuries. Due to the non-acute nature of diffuse trauma, they are challenging, if not impossible, to see on standard qualitative imaging. This is where quantitative DTI imaging is critical for proper patient diagnosis!
DTI sequences produce both qualitative as well as quantitative information. Using this technique we can produce high-resolution qualitative images that we can use to see an acute or focal injury, but also quantitative data we can tabulate and measure to evaluate for diffuse pattern injuries. Fractional Anisotropy maps (F.A. maps) are generated after the sequence is complete and subsequently used to measure the “health” or natural movement of water molecules along white matter tracts. If these tracts are broken or injured they will measure with decreased anisotropy (healthy motion). You can think of these maps as a neurological network of highways. Imagine anisotropy as traffic. Normal traffic is maintained if the roads are not damaged or closed off. If these do occur, traffic (anisotropy) slows down or ceases altogether. The brain works the same way: if white matter tracts are damaged, neurons do not travel as designed along the neurological axons.
Utilizing the FA map we can produce Diffusion Tractography images. Using this technique we can generate images that isolate specific white matter axonal tracts that are suspect of injury. They are displayed in a quantitative, easily explainable image that allows us to see the subtle injuries that standard imaging techniques are not capable of evaluating.
Why Is This Important?
Patients who sustain diffuse injuries to the brain often suffer from long-term neurological deficits that are subtle and hard to diagnose. DTI imaging provides a quantifiable imaging option from which to properly evaluate these patients. With accurate diagnosis, these individuals can move towards the proper treatment options that will help them move forward and recover.
At The Radiology Clinic, our responsibility to our patients and referring community is to provide an answer to their diagnostic questions through imaging. All studies performed at our practice are read by our team of highly experienced, fellowship-trained radiologists.
We are proud to offer this cutting-edge technology to our community and will continue to strive for excellence in radiology and the experience thereof.
For appointments or questions please call us at: 301-217-0500 or email: firstname.lastname@example.org
The Radiology Clinic
14995 Shady Grove Rd. Suite 140
Rockville, MD 20850