See Also: Brain Imaging and the Law
DOES YOUR PET BITE?
The Misapplication of Brain Scans in Toxic Tort
Brickford Brown and Samuel Tarry
In recent years, two exciting and relatively new
diagnostic medical procedures, PET and SPECT, have been propelled from the
hospital into the courtroom, most typically by plaintiffs. As a result, many
toxic and environmental tort defendants have faced the daunting task of
explaining, challenging, and refuting the dynamic color images of
plaintiffs’ brains provided by these computer-aided scans. Although untested
by appropriate peer review in the realm of toxic torts, both PET and its
less-expensive neuroimaging cousin, SPECT, do provide an indirect glimpse
into the functioning of the human brain. The compelling visual effects
virtually ensure a future proliferation of PET and SPECT scans proffered as
evidence of brain damage.
However, the diagnostic value of these neuroimaging
technologies is, at best, uncertain. Increasingly, lawyers and judges in
toxic tort litigation will have to wrestle with this controversy. Recent
experience suggests that the outcomes of these evidentiary battles may
determine, more than any other aspect of trial, a defendant’s judicial fate.
Until adequate testing and studies have been conducted, PET and SPECT should
not be allowed as proof of toxic brain injuries.
PET—Positron Emission Tomography—measures metabolism.
This is accomplished by injecting into the patient a radioisotope tracer
which "tags" glucose in the bloodstream. The PET scanner detects gamma rays
from the positron-emitting radioisotopes and generates an image of the
variations in metabolism across different sections of the brain. Although
this process obviously yields a snapshot of brain function, there is some
debate as to what "function" is being measured. As Jennifer Kulynych has
noted in "Brain, Mind and Criminal Behavior: Neuroimages as Scientific
Evidence," 36 Jurimetrics 235 (1996), to rely on PET images as a
measure of the brain’s cognitive activity requires one to assume that
changing metabolic rates actually represent the degree to which different
brain structures participate in thinking and reasoning.
The PET scanning process involves a needle, a patient,
and a radiology technician. A typical protocol starts with the technician
explaining the process to the patient and, if possible, to an accompanying
family member. After discerning the patient’s medical history, the
technician will have the patient lie down on a table. Often, this is done in
a dimly lit room in an effort to achieve a relaxed state. The technician
then inserts an IV and leaves the patient alone for ten to twenty minutes.
When the technician returns, he or she injects the patient with the
radioisotope. After another short wait, the IV is removed and the patient is
asked to return for scanning within a short time period which is dependent
upon the half-life of the particular radioisotope used.
The actual scanning looks and feels very similar to the
more commonly performed types of x-rays. The patient lies on a table which
slides into the middle of a circular scanner. With the patient’s head kept
in still position, the PET scanner collects multiple images of the patient’s
brain from different angles. The computer then processes the information
collected and produces color-coded images of metabolism throughout the
In 1996, there were 73 PET scanning sites in the United
States, located mainly at university medical centers in the East and
Midwest. Costs averaged approximately $1,000 per PET study. Because of the
spectacular nature of PET images, toxic tort plaintiffs appear more and more
willing to foot these bills in the hope of a larger reward. A review of
recent litigation demonstrates that plaintiffs often solicit PET scanning
after obtaining normal or "negative" results from more standard examinations
such as Magnetic Resource Imaging (MRI). As will be discussed later, the
ability of PET scans to aid in the diagnosis of chemically-induced brain
disorders is unproven and unsettled in the medical community.
SPECT—Single Photon Emission Computerized
Tomography—provides a cheaper alternative to PET scanning while achieving a
similarly impressive visual effect. Because the spatial resolution of SPECT
technology is inferior to PET, the resulting images are less exact, with the
colors tending to blur together. Technically, SPECT measures cerebral
metabolism only indirectly. It is viewed by clinicians as a cost effective
tool for gauging regional cerebral "perfusion" or blood flow. Although SPECT
technology was developed over twenty-five years ago, its use was limited
until recently due to the lack of effective tracers. By the end of 1996,
SPECT scanners far outnumbered PETs.
PET/SPECT in Toxic Tort Litigation
The most striking example of the persuasive power of
brain neuroimaging evidence is Guilbeau v. W. W. Henry Co., 85 F.3d
1149 (5th Cir. 1996). In Guilbeau, a Louisiana jury
returned a $2.9 million verdict to the plaintiff and his wife as damages for
chronic toxic encephalopathy (dementia). The plaintiff’s condition, which
was hotly disputed, allegedly resulted from a short-term exposure to carpet
adhesive containing either sodium pentachlorophenate or pentachlorophenol.
Following an $850,000 remittitur of the wife’s loss of consortium award by
the trial court, and a subsequent appeal, the United States Court of Appeals
for the Fifth Circuit reversed the verdict and rendered judgment for the
defendant, holding that no rational juror could find the defendant’s carpet
adhesive to be defective under Louisiana’s strict product liability law.
Plaintiff Guilbeau, a disabled mobile home salesman,
allegedly suffered from repeated dizziness, headaches, weakness, loss of
sleep, arm and wrist pain, fatigue, nervousness, itching, sweating, shaking,
and hallucinations. Mr. Guilbeau’s psychologist, Dr. Lisa Morrow, described
him as having a psychiatric disorder resulting from toxic exposure.
According to the plaintiff’s wife, he was sickened by odors of all variety
of substances, including shampoos and new clothing. Mrs. Guilbeau also
described temper tantrums, and explained the necessity of a sign placed on
the front door of their home which instructed visitors not to enter if they
were wearing hair spray, colognes, powder, make-up, or new clothes. The sign
thanked visitors for their efforts to help Mr. Guilbeau avoid "severe
seizures." Id. At 1156 fn. 21. As the Fifth Circuit noted
"amazingly," Mr. Guilbeau was fortunate enough to escape adverse effects
both from the fluid in his cigarette lighter and from the tobacco in the two
packs of cigarettes which he smoked daily. Id.
At trial, the plaintiff offered the testimony of Dr.
Thomas Callender, a board certified internist. Dr. Callender testified as an
expert in internal medicine, neurotoxicology, and occupational medicine. He
was allowed to opine that Mr. Guilbeau suffered from severe chronic toxic
encephalopathy caused by a two-week exposure to the adhesive. Dr. Callender
based his opinion on the plaintiff’s reported exposure history, his reported
hypersensitivity to smells, and a 1990 SPECT scan of his brain which showed
decreased blood flow in the left frontal lobe, the left thalamus, and parts
of the right basal ganglia. Plaintiff’s neurologist, Dr. Harper, concurred
with Callender’s diagnosis in spite of the fact that his own neurological
examination of Guilbeau rendered no abnormal physical findings aside from
the plaintiff’s complaints of odor sensitivity. Like Dr. Callender, Dr.
Harper’s opinion was based primarily on the SPECT scan, which showed
abnormal areas of decreased circulation in parts of Guilbeau’s brain.
Rather than launch a pre-trial assault on the SPECT
evidence through a Daubert hearing, the defendant chose to refute the
SPECT scan through cross-examination and the testimony of its expert, Dr.
Berger. On cross-examination, Dr. Callender was asked about his 1991
published article concerning the helpfulness of SPECT scans in diagnosing
toxic encephalopathy. Coincidentally, Dr. Morrow, the psychologist,
contributed to the article, which included a case study of Mr. Guilbeau. Dr.
Callender admitted that the defendant’s adhesive did not contain many of the
chemicals to which the article reported the plaintiff had been exposed. The
article, "Three Dimensional Brain Metabolic Imaging in Patients with Toxic
Encephalopathy," 60 Environmental Research, 295-319 (1993),
subsequently has been cited by other experts attempting to support the
proposition that SPECT scans showing decreased perfusion in the temporal and
frontal lobes are consistent with toxic encephalopathy. Dr. Harper admitted
on cross-examination that the SPECT scan was the "basic supporting" evidence
of his theory of toxic encephalopathy along with the plaintiff’s history.
Dr. Harper agreed that a SPECT scan is a measure of "blood flow" rather than
a test of "function" and admitted that a SPECT could not establish the
cause, date or duration of the decrease in perfusion. Dr. Callender,
however, who was not admitted either as a neurologist or a radiologist,
testified that he could infer actual brain damage on the basis of a SPECT
scan. Original Brief of Defendant/Appellant W.W. Henry Co., at 19.
The defendant also pointed out that the 1990 SPECT scan,
which was taken four years after the alleged exposure, showed decreased
blood flow primarily in the left hemisphere. Other evidence demonstrated
that the plaintiff had a fat-obstructed left carotid artery. An MRI of Mr.
Guilbeau’s brain revealed no structural damage or abnormalities. Additional
rebuttal evidence showed that a second SPECT scan, taken in 1993,
demonstrated normal blood flow in the left temporal lobe, left thalamus, and
right basal ganglia. Dr. Harper, who was unaware of the second SPECT until
the time of his cross-examination, conceded that the remaining area of
mildly abnormal perfusion in the left frontal area "would not explain most
of the complaints that we had talked about." Id. at 20. The
plaintiff’s psychologist, Dr. Morrow, further conceded that the article
which she co-authored with Dr. Callender was, to her knowledge, the first
case report of SPECT scan analysis of a patient reporting chemical exposure.
The jury was unmoved by defendant W.W. Henry Co.’s
efforts to explain or minimize the SPECT evidence. Indeed, courtroom
observers recall the color enlargements of Guilbeau’s brain SPECT as nothing
short of spectacular. According to one courtroom viewer, the pictures were
the centerpiece of Guilbeau’s case and "appeared to show that something was
clearly wrong with the [plaintiff’s] brain."
On appeal, Henry asserted that Guilbeau had failed to
present sufficient scientific evidence either of causation or actual brain
damage. Part of this argument included an assault on the reliability of
SPECT technology as a diagnostic tool for toxic encephalopathy. More
specifically, Henry challenged the admissibility of Guilbeau’s experts’
conclusions in that they were based on medically unfounded inferences about
the SPECT results. Henry rightly demonstrated the lack of medical studies on
the issue and correctly pointed out that even the World Health Organization,
which plaintiffs often cite as the oracle of toxic encephalopathy knowledge,
has concluded that tests for cerebral blood flow measurements among workers
exposed to toxic solvents are of poor diagnostic value. In his reply brief,
Guilbeau did little more than reiterate that SPECT scans "are well
recognized diagnostic tools," reference a TIME magazine article containing a
SPECT picture of a patient with attention deficit disorder, and reassert the
Callender article as valid support for his position. Original Brief of
Appellees/Cross Appellants, at 17.
Because the case was reversed based upon the
insufficiency of plaintiff’s proof of product defect under prior Louisiana
law, there is little indication of how the SPECT argument was received by
the Fifth Circuit. However, the written opinions suggest that even those on
the bench may have a tendency to get caught up in SPECT’s state-of-the-art
technology and overlook the void of medical and scientific support for its
use in diagnosing toxic brain injuries. In his dissenting opinion, sitting
Circuit Judge Reynado G. Garza flatly states his belief that Guilbeau
carried his burden. He writes: "the SPECT scan showed areas of decreased
brain function, which was consistent with toxic encephalopathy." 85 F.3d at
Judge Garza is not alone in his tacit acceptance of SPECT/PET
evidence in toxic tort cases. In Hose v. Chicago Northwestern
Transportation Co., 70 F.3d 968 (8th Cir. 1995), the court
upheld the limited use of PET scan evidence as an appropriate means of
eliminating alternative theories of injury advanced by the defense. The
obvious problem with this type of holding is that it allows evidence of a
differential diagnosis suggestive of causation. Simply put, a jury cannot be
faulted for attributing liability to a defendant when PET scan evidence
purports to discount all other potential causes of the plaintiff’s injuries.
The prejudice is compounded when, as in Hose, a radiologist is
allowed to testify that a PET scan is "consistent" with the plaintiff’s
alleged diagnosis and the suggested causation. Id. at 973.
In Hose, the plaintiff sued the employer railroad
pursuant to the Federal Employers Liability Act, alleging that he contracted
manganese encephalopathy as a result of work place exposures to manganese
fumes and dust between 1976 and 1991. Prior to litigation, Hose’s
neurologist, Dr. Jan Golnick, scheduled a PET scan for March 4, 1992. The
scan was interpreted by Dr. Naresh Gupta, a physician board certified in
nuclear medicine. Over the objection of defense counsel, the court allowed
the plaintiff to read into evidence Dr. Gupta’s deposition testimony
concerning his interpretation of the PET scan. Id.
Dr. Gupta’s testimony described the plaintiff’s PET scan
and explained why the images did not match the expected patterns for
Alzheimer’s, alcoholism, and stroke. Dr. Gupta then testified that the
plaintiff’s scan showed a pattern consistent with dementia and opined that
the plaintiff’s "overall picture is very consistent with manganese
encephalopathy and toxicity as the cause of this dementia." Appellant’s
Brief, at 32. The court admitted Dr. Gupta’s statement even though his other
testimony made it clear that the scientific literature had not adequately
described how a manganese toxicity would appear on PET. As defense counsel
pointed out, Hose’s PET scan showed a normal basal ganglia, the area most
often affected by manganese poisoning. An apparent abnormality in the basal
ganglia region detected in an April 1991 MRI had diminished by the time a
second MRI was taken in October of that year.
Ultimately, the jury believed Dr. Gupta’s PET evidence
and returned a $1.33 million verdict for Mr. Hose. On appeal, the Eighth
Circuit concluded that the district court did not abuse its discretion by
allowing Dr. Gupta to testify about the PET scan. 70 F.3d at 973. The court
seemed impressed by the fact that Hose’s treating physician ordered the PET
scan prior to the initiation of litigation, giving it the appearance of
being more diagnostic than calculated to create evidence for court. The
written opinion also included a reminder that challenges to the scientific
reliability of expert testimony should be addressed prior to trial. Id.
at 973 fn. 3. Ultimately, the court viewed Dr. Gupta’s body of testimony as
relevant because it was limited to showing consistency with, not diagnostic
proof of, manganese encephalopathy. Id. at 973.
Regardless of whether Dr. Gupta told the jury that the
PET scan showed manganese encephalopathy or was "consistent" with it, his
message was understood. The jury heard, and saw, evidence of what
misleadingly appeared to be a thoroughly performed differential diagnosis,
aided by reliable, high-tech equipment, which seemingly proved brain damage
caused solely by manganese toxicity.
When given the time to review the literature and educate
themselves about the limited application of PET and SPECT, courts are more
apt to see through the transparent shield of scientific reliability. In
Summers v. Missouri Pacific Railroad System, 897 F.Supp. 533 (E.D. Okla.
1995), the court examined SPECT technology in the scope of a pre-trial
Daubert hearing to exclude expert testimony concerning multiple chemical
sensitivity syndrome (MCS). Mr. Summers, along with co-plaintiff Potts, sued
his employer for MCS pursuant to the FELA. The plaintiffs claimed to have
been virtually disabled by exposure to diesel fumes while riding in the
second locomotive of a four locomotive train on a two-hour trip taken June
5, 1993. Their alleged symptoms included headaches, memory loss,
concentration difficulties, irritability, and fatigue.
Prior to trial, Missouri Pacific filed a motion to strike
the testimony of plaintiffs' expert, Dr. Alfred Johnson, a specialist in
"clinical ecology." Dr. Johnson diagnosed "chemical sensitivity" based upon
a physical examination, the plaintiffs' work history, and the results of a
Booth test, another procedure of questionable diagnostic value. Dr. Johnson
later ordered a SPECT scan which was interpreted as demonstrating a mismatch
between blood flow and function. Summers’s radiologist, Dr. Theodore Simon,
described these "abnormalities" as "typical of that seen in patients with
neurotoxic exposure." Dr. Frederick Bonte Dep., 18. As an instructional
tool, Missouri Pacific submitted, in its motion to exclude, the deposition
transcript of Dr. Frederick Bonte, a physician board certified in radiology
and nuclear medicine. Dr. Bonte criticized the methodology employed by Dr.
Simon in interpreting the SPECT scan, refuted his opinions, and discussed
the lack of reliable scientific and medical data to support the use of SPECT
technology to diagnose neurotoxic exposure. Id. at 24-35.
At the hearing, Magistrate Judge James H. Payne found
himself confronted with misleading statements about the nature of PET/SPECT
technology. For example, Summers’s attorney represented to the court that
the SPECT scan provided objective evidence of causation. "I mean, this is an
objective test. Yes, you can see the effects of what this material is." June
12, 1995 Hearing Tr., at 51. Fortunately, the Summers court reviewed
the necessary materials from which to learn about the application of PET/SPECT
and to make a proper ruling. The court ultimately granted Missouri Pacific’s
motion to exclude plaintiff’s expert testimony based on the lack of
reliable, scientific supporting evidence. In reaching its decision, the
court rejected the SPECT test as an acceptable means of diagnosing chemical
The record reveals that both of these tests [SPECT and
Booth] have been the subject of much criticism by the scientific community
as not having met acceptable scientific levels of methodology and criteria,
and are not designed to test for the recognized medical condition of
897 F.Supp at 540.
In 1991, the federal district court in Montana granted
summary judgment to Burlington Northern Railroad in a 27-plaintiff
consolidated FELA action alleging injuries from chemicals. Eggar v.
Burlington Northern Railroad Co., 1991 Westlaw 315487. The plaintiffs'
evidence included PET images. Burlington Northern’s motion, heard pretrial,
involved the admissibility of plaintiffs' expert testimony. Because the
court granted the motion based on broader aspects of reliability, it did not
reach the issue of whether PET scans offered appropriate diagnostic value in
the cases before the court. Id. at p. 4 fn. 9.
Similar situations have arisen in other areas of toxic
tort litigation. In 1991, Emma Jean Hando submitted a PET scan of her brain
to an administrative law judge in an effort to establish disability pursuant
to the Social Security Act, 42 U.S.C. 401-433. Ms. Hando's treating
physician had concluded that the PET scan was compatible with a diagnosis of
chemical sensitivity. The administrative law judge and the appeals counsel
rejected Hando's claim; the federal district court in Wyoming and the Tenth
Circuit Court of Appeals affirmed. Hando v. Shalala, 1993 Westlaw
423213, 13 F.3d 405 (10th Cir. 1993).
The Future of PET/SPECT
Although multiple chemical sensitivity syndrome has not
been widely recognized by the medical profession, certain physicians are
actively working to prove the disease and are employing neuroimaging as a
means to do so. Among others, Dr. Gunnar Heuser has been working to
establish before-and-after SPECT comparisons to demonstrate that MCS
patients show less blood perfusion in the temporal, frontal, and parietal
lobes following the inhalation of an offending substance. In his September
19, 1996 testimony before Congress, Dr. William E. Baumzweiger described Dr.
Arthur Vento's SPECT scan research on Gulf War veterans. Dr. Baumzweiger
stated that Dr. Vento has found persistent, if subtle, abnormalities in the
orbitofrontal, right hemisphere, and paralimbic timbic cortices which he
believes to be consistent with a brainstem-limbic system encephalitis. "The
Gulf War Disorders: Hearings Before the House Committee on Human Resources
and Government Oversight," September 1996 (statement of William E.
Baumzweiger, M.D.). PET and SPECT scans also have been utilized by certain
physicians investigating silicone toxicity in breast implant patients. A
recent case report on fifteen implanted women purports to demonstrate
abnormal SPECT scans showing decreased perfusion in the temporal lobes
bilaterally indicating impaired memory. According to the abstract, repeated
scans after the removal of the implants showed significant improvement in
most patients. Shoaib, Abnormal SPECT Scans and Impaired Memory in
Patients with Adjuvant Breast Disease (unpublished).
The increasing use of PET and SPECT scans by the medical
community, coupled with an awareness of their evidentiary potential by
lawyers, suggests that these scans will be used in greater numbers as
evidence of toxic brain damage. The United States Supreme Court's decision
in Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993),
with its perceived relaxation of standards for the admission of scientific
testimony, has encouraged the use of PET and SPECT scans to substantiate
claims of neurological injury due to toxic exposures. As discussed above,
the courts, in certain instances, are permitting the limited introduction of
this evidence despite the admonitions of the medical community that these
methods, except in limited circumstances, have not reached the level of
sophistication and reliability necessary to diagnose neurological or
It is well recognized that PET and SPECT scans can be
used in the management of patients with stroke, epilepsy, brain tumors, and
Alzheimers disease. Scan abnormalities have been recognized in patients with
an array of conditions such as depression, schizophrenia, and cerebral
vascular disease. While these techniques can be used to identify
abnormalities of the brain, there is not, at this time, adequate evidence to
support the confident use of PET and SPECT scans to establish causal
At best, the use of these techniques to establish
cause-and-effect in the area of toxic torts is premature. Before such
evidence is permitted, there must be accepted scientific evaluation to
establish supportable patterns of abnormalities associated with specific
conditions and their causes. This requires reliable, controlled studies of
patterns and conditions to establish a database of consistent information to
substantiate the relationships. Currently, sufficient data simply does not
exist to support the findings and conclusions offered by plaintiffs' experts
on the issues of causation and cognitive deficit.
In considering the admissibility of these neuroimaging
techniques, it is necessary to determine whether the methods are technically
adequate, whether a clear distinction can be made between "normal" and
"abnormal," whether sufficient reliability and validity have been
established, and whether science has demonstrated that the intended
application can be effective. The PET/SPECT expert should be able to
demonstrate to the court that the method has been adequately tested, based
on substantial peer-reviewed publications. He or she should also be able to
testify to the potential rate of error for the method as well as the
existence and maintenance of standards for controlling its use for clinical
applications. This is not possible in the context of the toxic tort case
because the data on which the plaintiffs' experts rely is without sufficient
Presently, the scans are so variable and subject to so
many dependent factors that it is impossible for a witness to testify with
intellectual honesty that the data currently available permits him or her to
determine the cause of any abnormalities seen on the scans.
First, the equipment comes in different configurations:
camera based and non-camera based. Of the non-camera based equipment there
can be single or multi-head systems, each potentially giving slightly
different resolutions. Generally speaking, the equipment is either high
resolution or low resolution. This makes a difference in the quality of the
scan and any subsequent interpretation. As an example, low resolution
scanners can produce artifacts in an image which can influence the
Similarly, the type of equipment employed must be
appropriate for the type of abnormality being investigated. Low resolution
equipment, which older scanners tend to be, may be appropriate for
identifying a large stroke, but may not be appropriate for locating a
temporal lobe seizure where high resolution is necessary.
Next, the quality of a specific scan is dependent on many
factors, including: the equipment used, the filters used, the tracers used,
the time between the tracer injection and the scan, the duration of the
scan, the mental state of the patient during the scan, movement of the
patient during the scan, audio and visual stimulation of the patient during
the scan, the alignment of the scanner to the patient, variations in the
processing and display of the scan, the method of reconstruction and
analysis, and the overall quality control of the scan.
Additionally, the typical methods of interpreting scans
are subjective and can vary from one interpreter to another, based on
experience, expertise, and/or clinical bias. Subjective differences in
interpretation can occur even between institutions, based on differences in
equipment, institutional experience, and protocols.
Finally, and perhaps most importantly, findings are
influenced by a lack of standardized definitions of "normal" and "abnormal,"
the lack of standardized quantitative analysis of the scan, the lack of
published standards for disease pattern identification, and the lack of a
recognized protocol for producing the scans to identify specific diseases.
The most basic parameters for scan interpretation, the terms "normal" and
"abnormal," do not have common and universal definitions. These "standards"
must, however, be developed in order to build the kind of information
storehouse which is necessary to support the diagnostic inferences currently
being made by certain experts.
It is difficult, though, if not impossible, to reach
agreement when the current data by which these terms would be defined has
been collected from instruments of varying resolution without standardized
scanning, reconstruction and interpretation protocols. This lack of
appropriate controls ensures that there is inadequate underlying data on
which the inferences drawn or reached by plaintiffs' experts can be
The attempts at authentication of PET and SPECT scans
also can be fertile ground for objection at trial by defense counsel.
Generally, no single witness is expert in all aspects of producing and
reading a brain scan. Neuroimaging is multifarious and oftentimes requires
one image study to be reviewed by physicists, radiologists, psychiatrists,
psychologists, neurologists, and biochemists. When, however, the image is
offered as evidence at trial, the issue of diagnostic inference is usually
addressed by only one witness, a neurologist or an internist, who has only
limited knowledge of the technical aspects of producing an image, aspects
which affect the image's appearance.
It is accepted that new medical diagnostic techniques
eventually make their way into the courtroom. It is necessary, thought, for
courts to adhere to procedural safeguards when scrutinizing testimony about
these techniques. Danger lies in the fact that PET and SPECT scans have an
alluring power. They appear as living photographs of the structure and
function of the brain and over-simplify complicated data about the brain.
These "photographs" of the brain suggest a portrait of scientific
objectivity where none exists. In reality, PET and SPECT scans are more akin
to charts and line graphs than to photographs. The admission of the
accompanying testimony interpreting "objective" scans and linking blood flow
or metabolism with a substance-induced injury is an insupportable and
dangerous move by the courts.
The courts, therefore, must define the appropriate use of
neuroimaging evidence. Legal procedure demands that courts rigidly apply the
appropriate evidentiary tests to determine the admissibility of PET and
SPECT studies. If the traditional standards for the admission of scientific
evidence are used, there is no doubt that this evidence will be excluded.
Until valid medical and scientific research establishes that PET and SPECT
scans can demonstrate neurological and cognitive deficits, along with their
causes, judges should keep such testimony out of the courtroom. The
propriety of expert findings and conclusions of cognitive deficiencies
resulting from exposure to toxic substances, based on PET or SPECT studies,
is impossible to substantiate based on the current level of scientific and
Reprinted with permission from For the Defense,
Vol. 39, No. 3, March 1997 Defense Research Institute, Inc.