Congress NFL Hearings: Dr. Benson on Susceptibility Weighted Imaging

Randall Benson, M.D. on Neuroimaging Advances – SWI

As I have stated here and elsewhere, diagnosing accidental concussions involves reconstructed evidence and the reliance on history from someone who likely has memory problems as to what happened, because they were concussed. In contrast to football or boxing concussions, real world concussions are rarely witnessed in the critical 30 second time window when the evidence is the clearest. See today’s blog at http://www.subtlebraininjury.com/blog/2010/01/evolution-in-understanding-of_07.html

Thus, with such an imperfect diagnostic process I am always hoping that the newest neuroimaging technique can provide us with a bright light of “objective evidence” of injury. I have heard Dr. Randall Benson speak and his state of the art imaging techniques are the most promising of any of those I have seen to date. Dr. Benson testified to Congress about the advances being made in those techniques, principally through new ways of using the familiar MRI scanner.

Dr. Benson testified principally to two state of the art methods of using MRI, Diffusion Tensor Imaging (“DTI”) and Susceptibility Weighted Imaging (“SWI”).

Dr. Benson said in his prepared remarks:

Most of our work has used victims of transportation related injuries and falls, however our principle research focus has always been closed head injury, under which concussion falls and is otherwise known as mild head injury. I will also include some examples of former players scans. The focus of my testimony will be susceptibility-weighted imaging (SWI) and diffusion tensor imaging (DTI).

I have been using DTI for years now in our forensic cases, with significant success, but SWI is something new to me. Dr. Benson explained SWI as follows:

Susceptibility-Weighted Imaging (SWI) Imaging research of TBI began at WSU in 2004 when an eleven year old boy (C.G.) survived after his family’s ATV skidded off a mountain road in Colorado plunging 200 ft. He was still in coma two months later when we scanned him at WSU. His CT and standard MRI revealed a skull fracture and atrophy but not much more. Figure 1 compares a standard, clinically available T1-weighted image with a susceptibility-weighted image (SWI) through the temporal lobes and brainstem for C.G. sixty days after injury. Note the many “black holes” present in the
SWI image which are small (“micro”) hemorrhages indicating severe diffuse axonal injury (DAI) from TBI.

Developed by Mark Haacke, SWI is extremely sensitive to iron and blood products and detects microhemorrhages where conventional MRI fails. SWI detects hemorrhage at all stages, since iron remains even after the fluid from blood is reabsorbed. Prior work by Dr. Haacke with Loma Linda University (Karen Tong, M.D.) had demonstrated the value of SWI for detecting DAI in children with “shaken baby syndrome” where it was five times more sensitive than gradient echo imaging. In a series of 20 TBI patients (transportation related and falls) varying in severity and elapsed time since injury, we found an excellent correlation (Ρ =0.54) between total hemorrhage volume and the number of days in post-traumatic amnesia which is known to be a good T1‐Weighted SWI predictor of one-year neurological outcome (JMRI, 2009). We have, since 2004, scanned over 100 TBI patients with SWI at WSU alone and a similar number at Loma Linda. In addition to TBI, it is being used in stroke, cerebral amyloid angiopathy (CAA) (Figure 2), Alzheimer’s disease and disorders of iron metabolism. SWI is now clinically available on GE and Siemens MRI scanners.

Every few years, I get newly excited about a neuroimaging technique that will give us a bright line of diagnosis for those with long term problems after a concussion. In 2000 what gave me great hope was learning about the development of techniques to see hemosiderin staining, principally the technique Gradient Echo Imaging. The theory of Gradient Echo Imaging is that when bleeding in the brain occurs, it leaves behind iron deposits, even after the there is no liquid blood visible on a CT or MRI. Those iron deposits are the hemosiderin. The hemosiderin is highly magnetic because it is principally iron. So if the magnet in the MRI is tuned precisely, this imaging technique can show evidence of a non-acute bleed, in theory years after the original injury. Here is a comparison between a conventional MRI image and the SWI image. The SWI is on the right and of import is the small black circles which don’t appear on the image to the left.

Figure 1. Comparison of T1 and SWI images for C.G. Note the many dark
“holes” in the SWI image that are not present on the T1 weighted image. These
“black holes” are caused by signal loss induced by paramagnetic hemoglobin or
other iron containing blood products.

It was exciting when I learned about Gradient Echo Imaging. It has not had any actual value in my cases. The exciting news about SWI is that it is five times more sensitive than Gradient Echo Imaging. The challenge in neuroimaging is whether five times better is enough when you are talking about multiplying zero. The math analogy isn’t totally valid, but if no hemosidrin deposits show up on even disabling mild traumatic brain injury cases, it may very well be that the kind of bleeds that leave hemosiderin behind are not the principal culprit in the Post Concussion Syndrome. Time will tell.

Diffusion Tensor Imaging (DTI) is more focused at the likely pathology, injury to the axons. We will discuss Dr. Benson’s testimony about DTI in our next blog.