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An Introduction to Structural Brain Imaging for Traumatic Brain Injury (TBI)

San Francisco TBI Brain Imaging Lawyers

The San Francisco brain injury attorneys at Abramson Smith Waldsmith LLP, work closely with clients to ensure they receive an accurate diagnosis and appropriate medical treatment for their injuries. Our experience handling such cases, and our access to medical and investigative experts, have enabled us to build a track record of successful results for our clients. To learn more, contact a personal injury lawyer at our law firm to schedule a free initial consultation.

Mild and moderate TBI sometimes have no positive or visible “structural” defects.  These are truly invisible injuries.  As a result, advancing cases involving such injuries necessitates the use of oral testimony of neurologists and neuropsychologists to prove injury.  Although psychometric testing performed by these experts can be “objective,” it is not as objective or convincing as “seeing” an injury on a brain imaging study.  It is always best to correlate psychometric testing with imaging when possible.

Imaging techniques are constantly improving, now providing the ability to visualize brain activity and function on the cellular level.  The newest of techniques are routinely used by neuroscientists across the world.  It is just a matter of time before these techniques and studies all admissible in a court of law to prove TBI.

A lawyer representing TBI victims must have intimate knowledge of imaging to effectively represent his client because these images give the client a distinct advantage in proving his case.  These studies are expensive, and one must be sure that the attorney he selects has the resources to get the best imaging studies available to increase the chances of full compensation for the brain injury.

The various types of imaging studies are commonly admitted into evidence at trial with the proper expert foundation include:


X-rays have been around for a very long time (1895) and are excellent at showing skull fractures and other bony injuries.  They are of no assistance in visualizing or differentiating soft tissues like the brain.

CT scans

Computed tomography is based on the measurement of the amount of energy that the head absorbs from a beam of radiation that passes through it from a source to a detector.  The radiation source and detector within a CT scanner are mounted opposite one another along a circular track, or gantry, allowing them to rotate rapidly in a synchronized manner around the table on which the patient lies.

A computer controls the radiation source, the rotation of the radiation tube, and the detector, and the movement of the table.  Measurements taken in anatomical slices, or tomograms, are then stored on a computer.  The “tome” in tomography is the Greek word for “slice.”

CT scans capture density, or mass per unit volume.  Pixel intensities are mapped to allow reliable discrimination between different densities of tissue such as air, water, fat, bone, and various brain components.  The denser the material (e.g., metal or bone), the brighter it appears in CT images.  In turn, less dense tissue (e.g., fat and water) appears darker.

CT scans reveal much more detail than a regular x-ray.  Physicians have the option of studying a scanned brain one slice at a time or stacking the slices to create a full 3D model.  CT scans are the gold standard for showing brain swelling, brain bleeds, enlarged ventricles (containing cerebrospinal fluid), and encephalomalacia.

MRI scans

Magnetic resonance imaging (MRI) interprets signals derived from water molecules.  The human body is full of water molecules, each of which has two hydrogen nuclei (H2O) also known as protons.  These protons line up in the direction of the imposed magnetic field and radio waves (i.e. a signal) detectable by the scanner.  The computer uses this signal to produce high resolution images.  MRI can distinguish between fat, air, blood, and water within a given structure in the brain.  No radioactive material is necessary to obtain this image so the scan is harmless.  MRI produces two-dimensional images that consist of individual slices of the brain.  The latest technology allows the slices to be lined up to create a full 3D model of the brain.

The MRI table or scanner does not move to cover different slices in the brain.  Rather, images can be obtained in any plane through the head by electronically “steering” the plane of the scan.  The switching on and off of these magnetic field gradients are the source of the loud clicking and whirring noises that are heard during an MRI scan.  This process requires more time than CT scanning.

MRI scans are used to image all areas of the body but are particularly useful for visualizing tissues with many hydrogen nuclei or protons and little density like the brain, muscles, tumors, etc.  MRI scanners come in different magnetic powers.  They vary from 1.5 Tesla, 3.0 Tesla, 4.0 Tesla, to 7.0 Tesla.  The rule is the higher the Tesla magnetic rating, the higher the resolution of the scan.  It is preferable to at least obtain a 3.0 Tesla where possible.

 CT Scan vs. MRI

CT and MRI are complementary techniques, each with its own strengths and weaknesses. The choice of which examination is appropriate depends upon how quickly it is necessary to obtain the scan, what part of the head is being examined, and the age of the patient, among other considerations.

Advantages of Brain CT Scans

  • CT scans are much faster than MRI, thus preferred in cases of emergency and trauma
  • CT scans cost less than MRI
  • CT scans are less sensitive to patient motion during the examination
  • CT scans are usually easier for claustrophobic patients to handle
  • CT scans present no risk to patients with implantable medical devices, such as pacemakers

Advantages of Brain MRI

  • MRI does not use ionizing radiation, thus is preferred in children
  • MRI depicts brain anatomy and abnormalities in greater detail
  • MRI does not require the patient to physically move
  • MRI presents a much smaller risk of causing potentially lethal allergic reaction
  • MRI can show structures that may be obscured by bone in CT images

DTI (diffusion tensor imaging)

In addition to the brain functional imaging techniques, the newest study is DTI (diffusion tensor imaging).  This is a more sophisticated MRI imaging method which allows one to visually track nerve fibers to see if there are disruptions from injury.  It allows one to estimate the damage to nerve fibers that connect the white matter of the brain.  DTI measures the restricted diffusion of water through brain tissue.  Water does not freely diffuse in all directions in the brain because surrounding tissues limit its movement creating preferred directions of water diffusion.  It is easier for water to diffuse along the length of a white matter nerve fiber than across it.  The way that nerve fibers are oriented determines how the water flows.  Parallel bundles of nerve cells make diffusion of water molecules easier along the main direction.  This concept can be imaged and measured.  DTI can be used to track a nerve fiber or path through which information travels in the brain.  Tractography is showing the path of neural information from the brain, down the spinal cord and to the peripheral nerves.  These color images of nerve fiber tracts are very dramatic.

Functional Brain Studies

There are also three exciting imaging studies that focus on brain “function” rather than just on “structure”:  PET scans, fMRI and SPECT scans.  These techniques allow one to show the effect of a TBI on the brain without having to rely solely on the testimony of experts.  Of course, expert testimony would be needed to try to lay the necessary evidentiary foundation for these imaging studies.

 PET scans

PET is an acronym for “positron emission tomography.”  This technique has been available since the 1970’s but has undergone a good deal of advancement in quality since then.  It relies on a small amount of radionuclide (a tracer or isotope) that is injected into the body.  The tracer is chemically mixed into a biologically active molecule that the body will absorb and use.  The most common molecule used is FDG, which is a sugar analogue (i.e. a cousin) of glucose.  The goal is to wait and see how the brain absorbs and metabolizes the glucose.  If the brain does not absorb or metabolize the glucose at all or does so poorly, there is abnormal metabolism (hypometabolism).  This is evidence that the brain in the area being studied either is not functioning or not functioning efficiently.

PET scans provide dynamic information about the working brain which can help illustrate brain injury that might be missed by less sensitive structural imaging like CT or MRI scans.

The scanner creates 3D-colored images of the brain with excellent resolution.  PET scans can show deficits in areas of the brain responsible for attention, memory, mood regulation etc.  For example, CT scans of anoxic brain injuries (lack of oxygen), hypoxic brain injuries (reduced oxygen) due to carbon monoxide poisoning (COI), anesthesia, or birth injuries, are often negative.  Often the only way to visualize these brain injuries is with a PET scan.

The admissibility of a PET scan into evidence at trial depends on a strong expert foundation.  Opponents of admissibility argue that the PET scan is not a generally accepted or scientifically reliable method of measuring brain function.  They cite Daubert v. Merrell Dow Pharmaceuticals, Inc, 509 U.S. 579 (1993) and Frye v. United States, 54 App. D.C. 46, 47, 293 F. 1013, 1014 (1928). Frye held that scientific evidence can be admitted only if it has gained a general acceptance in a particular field. Daubert held that Federal Rules of Evidence, Rule 702 superseded Frye as the proper standard for determining the admissibility of scientific evidence in the federal courts. Rule 702’s two-part test for determining admissibility of an expert opinion is: 1) Does the opinion of the expert relate to a matter of scientific, technical, or specialized knowledge, and 2) Will the expert’s testimony be helpful to the trier of fact in determining a fact in issue in the case?

As PET scanning continues to advance, it will be easier to establish that this imaging technique is admissible.  The highest resolution available is HRRT (high resolution research tomography).  There are only five in the US and thirteen in the world.  A resource for HRRT PET scanning is the University of California, Irvine Brain Imaging Center in Irvine, California (949-824-7867).  Anyone attempting to admit a PET scan into evidence should make sure to retain a knowledgeable expert to lay the proper foundation.


This is the acronym for the “functional MRI.”  CT and MRI scanning can give one a 3D model of organ structure or anatomy but fMRI takes this a step further.  It measures brain activity, based on the same technology as the MRI.  Both techniques use a strong magnetic field and radio waves (signals) to create detailed images.  Whereas traditional MRI creates images only, fMRI looks at blood flow in the brain to detect areas of activity, i.e. changes in blood flow otherwise known as hemodynamics.

Oxygen rich blood and oxygen poor blood behave differently in a magnetic field.  They have different magnetic resonances.  Contrast in blood oxygen response enable the scanner to map images of brain activity to tell physicians which parts of the brain are more active or less active.  Increased blood flow translates to increased brain activity and vice versa.

fMRI has been around since the 1990’s and is primarily used as a research tool.  It has dominated the brain mapping field because changes in blood flow and blood oxygenation are closely linked to brain activity.  Its advantages are that is uses no radiation like X-rays, CT scans, PET scans and SPECT scans, and has no risks.  It produces very high-resolution images.  It also can record signals from all regions of the brain unlike EEG (electroencephalogram) which focuses mainly on the surface of the brain.

Although it is a revolutionary technique it is not without disadvantages.  It is expensive.  It only looks at blood flow and not the activity of individual brain cells (neurons). Just because a brain area “lights up” on an fMRI scan for decreased blood flow, it is not conclusive proof that a particular type of brain activity is being compromised.  One has to deduct this because individual neurons are not visualized.

fMRI scans are not routinely admitted into evidence at trial.  The challenge is that this scan is neither generally accepted nor scientifically reliable, as discussed above with the admissibility of PET scans.

SPECT scans

This is an acronym for “single photo emission computed tomography.”  It is essentially a CT scanner and a radioactive tracer.  It provides information regarding blood flow to the brain.  The tracer is injected and then is absorbed as it is circulated in the blood stream.  A camera detects the photos and this information is transmitted to a computer and cross-sectional images are converted to 3D format.  The study shows how the blood flows through the brain.

SPECT scans have been available since the 1970’s.  They are cheaper than PET scans but are of lower resolution.  fMRI is a similar measurement and is safer because no isotopes are used.

Our job is to ensure the responsible party is held accountable and to secure full and fair compensation. We invite you to review some of the verdicts and settlements  we’ve recovered for past clients with closed head injuries or traumatic brain injuries.

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For more information or to schedule a free initial consultation with an experienced personal injury lawyer, contact Abramson Smith Waldsmith LLP. Or call us at 415-421-7995 or toll free at 866-399-3548.