CT indicates computed tomography. The number of patients presenting
with head injury (n=6936) is an estimate based on the proportion of patients
included from the total number of trauma patients seen by a neurologist-in-training
in the emergency department of the participating center, which included the
majority of patients.
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Smits M, Dippel DWJ, de Haan GG, Dekker HM, Vos PE, Kool DR, Nederkoorn PJ, Hofman PAM, Twijnstra A, Tanghe HLJ, Hunink MGM. External Validation of the Canadian CT Head Rule and the New Orleans
Criteria for CT Scanning in Patients With Minor Head Injury. JAMA. 2005;294(12):1519–1525. doi:10.1001/jama.294.12.1519
Context Two decision rules for indications of computed tomography (CT) in patients
with minor head injury, the Canadian CT Head Rule (CCHR) and the New Orleans
Criteria (NOC), suggest that CT scanning may be restricted to patients with
certain risk factors, which would lead to important reductions in the use
of CT scans.
Objective To validate and compare these 2 published decision rules in Dutch patients
with head injuries.
Design, Setting, and Patients A prospective multicenter study conducted between February 11, 2002,
and August 31, 2004, in 4 university hospitals in the Netherlands of 3181
consecutive adult patients with minor head injury who presented with a Glasgow
Coma Scale (GCS) score of 13 to 14 or with a GCS score of 15 and at least
1 risk factor.
Main Outcome Measures Primary outcome was any neurocranial traumatic finding on CT scan. Secondary
outcomes were neurosurgical intervention and clinically important CT findings.
Sensitivity and specificity were estimated for each outcome for the CCHR and
the NOC, using both rules as originally derived and also as adapted to apply
to an expanded patient population.
Results Of 3181 patients with a GCS score of 13 to 15, neurosurgical intervention
was performed in 17 patients (0.5%); neurocranial traumatic CT findings were
present in 312 patients (9.8%). Sensitivity for neurosurgical intervention
was 100% for both the CCHR and the NOC. The NOC had a higher sensitivity for
neurocranial traumatic findings and for clinically important findings (97.7%-99.4%)
than did the CCHR (83.4%-87.2%). Specificities were very low for the NOC (3.0%-5.6%)
and higher for the CCHR (37.2%-39.7%). The estimated potential reduction in
CT scans for patients with minor head injury would be 3.0% for the adapted
NOC and 37.3% for the adapted CCHR.
Conclusions For patients with minor head injury and a GCS score of 13 to 15, the
CCHR has a lower sensitivity than the NOC for neurocranial traumatic or clinically
important CT findings, but would identify all cases requiring neurosurgical
intervention, and has greater potential for reducing the use of CT scans.
Head injury is one of the most common injuries in the Western world
with an estimated incidence of hospital-treated patients with minor head injury
of 100 to 300 per 100 000 population.1 Minor
head injury is commonly defined as blunt trauma to the head, after which the
patient has lost consciousness for less than 15 minutes or has a short posttraumatic
amnesia of less than 1 hour, or both, as well as a normal or minimally altered
mental status on presentation (a Glasgow Coma Scale [GCS] score of 13-15).2,3
Intracranial complications of minor head injury are infrequent (6%-21%)
but potentially life-threatening and may require neurosurgical intervention
in a minority of cases (0.4%-1.0%).3-8 Neurocranial
injury that does not require neurosurgical intervention may still cause significant
clinical problems; these patients will usually be kept under close clinical
observation. Computed tomography (CT) of the head is the imaging modality
of choice for diagnosing neurocranial traumatic lesions, such as skull fractures,
epidural and subdural hematomas, and hemorrhagic contusion. In many Western
countries, CT is therefore routinely used to evaluate patients with minor
head injury for the presence of neurocranial complications.
A study by Haydel et al7 suggested that
CT is only indicated in patients with minor head injury with 1 of 7 risk factors
(the New Orleans criteria [NOC]) (Table 1).
According to this decision rule, patients without any risk factors would not
require CT scanning and implementation of this rule in the United States was
estimated to reduce CT scans performed for minor head injury by 23%. A similar
study by Stiell et al3 identified a different
set of risk factors, the Canadian CT Head Rule (CCHR) (Table 1). The potential reduction in the number of CT scans by implementing
this decision rule was estimated at 46%. Both decision rules had 100% sensitivity
for identifying patients with traumatic brain injury, as is desirable according
to a survey of emergency physicians, but both rules had low specificities.9
Proper external validation of these published decision rules is necessary
before they can be implemented. Our goal was to externally validate these
2 decision rules, the NOC and the CCHR, in a large multicenter study in the
In our prospective multicenter study, data were collected on 3364 consecutively
included patients between February 11, 2002, and August 31, 2004, in 4 Dutch
university hospitals (Figure). Patients
were included if they presented within 24 hours after blunt head injury, were
older than 16 years, and had a GCS score of 13 to 14 or had a GCS score of
15 with 1 of the following risk factors: history of loss of consciousness,
short-term memory deficit, amnesia for the traumatic event, posttraumatic
seizure, vomiting, severe headache, clinical evidence of intoxication with
alcohol or drugs, use of anticoagulants or history of coagulopathy, physical
evidence of injury above the clavicles, and neurological deficit. Patients
were excluded if a CT scan could not be performed due to concurrent injury
or if there were contraindications to CT scanning.
After review of our study protocol, patient informed consent was waived
by the institutional review board and medical ethical committee, because patients
meeting our inclusion criteria routinely undergo a head CT scan according
to most local hospital policies, as is recommended in the current Dutch guidelines.10
Patients were considered to have lost consciousness when reported by
a witness or by the patient. Loss of consciousness was not considered an obligatory
criterion for inclusion in study, as was the case in previously published
studies, but rather as one of the risk factors for neurotraumatic findings.
A deficit in short-term memory was defined as a persistent anterograde amnesia.
If the patient could not recall the entire traumatic event, this was considered
as amnesia for the traumatic event. Posttraumatic seizure was classified as
either a witnessed or suspected seizure after the traumatic event. Vomiting
included any emesis after the traumatic event. Headache included both diffuse
and localized pain. No blood toxicology tests were performed to assess severity
of intoxication; presence and severity of intoxication were evaluated clinically,
evidenced by slurred speech, alcoholic fetor, or nystagmus. Anticoagulant
treatment included only warfarin and not platelet aggregation inhibitors (eg,
aspirin, clopidrogel). Presence of coagulopathy was assessed by patient history;
no blood coagulation tests were performed. Physical evidence of injury was
defined as clinically significant discontinuity of the skin or extensive bruising.
Focal neurological deficit was defined as any abnormality on routine clinical
neurological examination, indicating a focal cerebral lesion.
All patients were examined by a neurologist or a neurologist-in-training
under the supervision of a neurologist. All included patients underwent head
CT scanning following physical examination. CT scanning was performed according
to a routine trauma protocol, which consisted of a maximum slice thickness
of 5 mm infratentorially and 8 mm supratentorially, without intravenous contrast
administration. All scans were interpreted by a neuroradiologist or a trauma
radiologist in bone and brain window settings. The reading radiologist was
not blinded to the patient’s clinical information, because all reading
was performed in a clinical setting to evaluate the validity of the decision
rules in daily practice.
Data were collected on patient and trauma characteristics (age, sex,
time of injury and presentation, intoxication, anticoagulant treatment), accompanying
symptoms (loss of consciousness, posttraumatic amnesia, posttraumatic seizure,
short-term memory deficits, headache, vomiting), as well as on physical and
neurological examination, CT findings, and the need for neurosurgical intervention.
Selection of items was based on a literature review of published risk factors
for intracranial complications after minor head injury. Data on patient history
and examination were entered by the examining physician into a database11 before the patient underwent CT, unless this interfered
with the clinical work flow, in which case data were entered after the CT
was performed.12 CT findings were added separately
by the reading radiologist (H.M.D., D.R.K., P.A.M.H., and H.L.J.T.). Data
on neurosurgical intervention were collected by searching the included patients’
records in the hospital patient information system.
Our primary outcome measure was any traumatic finding of the neurocranium
on the CT scan. Findings on the CT scan that led to neurosurgical intervention,
although more important from a clinical point of view, were considered a secondary
outcome, because of their low frequency and potential clinical variability
across centers. However, because of their clinical significance, they will
be reported first. A neurosurgical intervention was defined as any neurosurgical
procedure (craniotomy, intracranial pressure monitoring, elevation of skull
fracture, ventricular drainage) within 30 days after the traumatic event.
Findings on the CT scan, which we considered to be important for clinical
practice in that the patient would generally be admitted to hospital, were
also considered a secondary outcome measure. These were defined as any intracranial
traumatic finding on the CT scan, including depressed skull fractures.
To reliably validate the published decision models for predicting neurocranial
traumatic findings on CT scan, a minimum of 100 events of our primary outcome
were needed.13,14 Given an incidence
of traumatic findings on CT of 8% to 10%, at least 1250 patients who fulfilled
the inclusion criteria of the original decision rules would need to be included.15
Patient data entered in the database were assessed by one of the authors
(M.S.) for correct patient inclusion and for completeness of the data. Missing
data of patients included in the analysis were assumed to be missing at random
and imputed based on the available data means to avoid bias. The proportion
of imputed missing data was 3.81%, which included both items documented as
unknown and items that were not documented. We evaluated our patient population
for demographic characteristics, mechanism of injury, traumatic findings,
neurosurgical intervention, and occurrence of the risk factors of both decision
We determined the sensitivity and specificity (and 95% confidence intervals
[CIs]) for neurosurgical intervention, neurocranial traumatic findings on
CT, and clinically important lesions on CT of both decision rules.16 The decision rule was considered positive when at
least 1 of the risk factors was present. For the CCHR, in which a distinction
is made between high-risk and medium-risk criteria, we chose not to use this
distinction; therefore, all risk factors were considered equally important.
The published decision rules were designed for specific patient populations,
which were more restricted than our patient population. We therefore first
performed our validation analyses in the subgroup of patients for whom the
decision rule was designed (Table 1);
these decision rules are referred to as the original decision rules. We then
adjusted the original decision rules for use in our entire study population,
which also included patients without a history of loss of consciousness, by
adding the exclusion criteria of the original rules as additional risk factors,
which are referred to as the adapted decision rules. This means that the adapted
NOC decision rule also included the risk factors neurological deficit and
a GCS score of 13 or 14, and the adapted CCHR decision rule included the risk
factors anticoagulation, posttraumatic seizure, and neurological deficit in
addition to the original risk factors. The potential reduction in emergency
CT scans was estimated by assuming that if the rule were to be adapted, then
a positive result on the rule would be followed by a CT scan and a negative
result on the rule would not.
Data were analyzed using SPSS version 12.0 software (SPSS Inc, Chicago,
Ill); P<.05 was considered statistically significant.
The total number of patients presenting with head injury during our
study at the 4 centers was estimated to be 6936 (Figure). A total of 3572 patients were not included because they
did not meet the inclusion criteria. Of the 3364 patients originally included
in the study, 112 did not meet the inclusion criteria on reassessment and
were excluded from further analysis. One patient had a contraindication for
CT, 1 was not seen by a neurologist, 16 patients did not have CT performed
because of logistical reasons, 14 patients had no available data on patient
history, and 39 patients had no available data on neurological examination.
These patients were also excluded from further analysis, resulting in 3181
patients in the data analysis.
Patient characteristics are shown in Table
2. A total of 304 patients had neurological deficit, including 64
patients (21%) with lateralized motor weakness, 60 patients (20%) with lateralized
sensory disturbances, and 251 patients (83%) with focal neurological deficits.
Focal neurological deficits included, among other deficits, pathological reflexes
(37%), nystagmus (19%), visual disturbances (9%), and pupil abnormalities
(6%). In our study population, relatively few patients had posttraumatic seizure
(0.7%), clinical signs of skull fracture (2.1%), or use of anticoagulation
Most patients presented with a normal GCS score of 15 (Table 3). Neurosurgical intervention was required in 17 patients
(0.5%), which was performed for epidural hematoma in 8 cases, subdural hematoma
in 3 cases, depressed skull fracture in 3 cases, and a combination of extra-axial
hematoma and depressed skull fracture in the remaining 3 cases. Neurocranial
traumatic lesions on the CT scan were found in 9.8% of the patients, with
the highest proportion of traumatic findings in the category of patients with
a GCS score of 13 (24.5%). The most common traumatic finding on the CT scan
was a skull fracture (59.6%) (Table 4).
Clinically important lesions were present in 243 patients (77.9%). Epidural
hematoma was present in 11.2% of patients with traumatic findings; most of
these hematomas were small with no or only localized mass displacement (25
of 35 cases) and were likely to be venous in origin in 4 cases. Subdural hematoma
was present in 67 patients (21.5%) with traumatic findings on CT, and also
was small in most cases with no (42 patients) or minimal (14 patients) mass
Notably, in 5 (29%) of 17 patients who underwent neurosurgical intervention,
no history of loss of consciousness was present. A history of loss of consciousness
was also absent in 85 (27%) of 312 patients with neurocranial traumatic CT
findings and in 61 (25%) of 243 patients with clinically important CT findings.
For both the NOC and CCHR decision rules, both original and adapted,
sensitivity for identifying patients who underwent neurosurgical intervention
was 100% (Table 5). Sensitivity for
neurocranial traumatic lesions on the CT scan, however, was not 100% for both
rules. The adapted NOC reached the highest sensitivity for identifying patients
with neurocranial traumatic findings on the CT scan (99.4%; 95% CI, 97.7%-99.8%);
the original CCHR had the lowest sensitivity (83.4%; 95% CI, 77.7%-87.9%).
Two patients with neurocranial traumatic CT findings were not identified using
the adapted NOC rule. One of these patients with a nonhemorrhagic contusion
would have been identified by the adapted CCHR because of the presence of
prolonged (>30 minutes) posttraumatic amnesia. With the adapted CCHR, 47 patients
with traumatic findings would have been missed; 46 of these patients would
have been identified with the adapted NOC, because of the presence of external
injury above the clavicles other than clinical signs of a skull fracture (41
patients) or headache (5 patients). Traumatic findings on the CT scan in these
patients included skull fracture (n = 30), subdural (n = 5)
and epidural (n = 2) hematoma, subarachnoid hemorrhage (n = 12),
hemorrhagic (n = 11) and nonhemorrhagic (n = 1) contusion,
and diffuse axonal injury (n = 2). One patient with diffuse cerebral
swelling did not have any risk factors using either the CCHR or NOC decision
rules. Sensitivity for clinically important traumatic CT findings was very
similar to that for all neurocranial traumatic CT findings for both decision
Specificity for neurosurgical intervention and neurocranial traumatic
CT findings was very low for the adapted NOC decision rule but higher for
the adapted CCHR decision rule (Table 5).
Specificity for clinically important traumatic CT findings was almost identical
to that for all neurocranial traumatic CT findings for both decision rules.
The potential reduction in emergency CT scans by using these decision rules
would have been higher with the adapted CCHR rule (37.3%; 95% CI, 35.6%-39.0%)
than with the adapted NOC rule (3.0%; 95% CI, 2.4%-3.6%).
In this multicenter prospective validation study of 2 published decision
rules for the use of CT scanning in patients with minor head injury, we found
that both the NOC and the CCHR had 100% sensitivity for identifying patients
who underwent neurosurgical intervention after minor head injury. This was
true for both the original decision rules (when applied to the patient population
these rules were designed for) and for the adapted rules applied to our entire
study population. Sensitivity for neurocranial traumatic CT lesions or for
clinically important lesions, however, was not 100% for both rules. The NOC
decision rule had high sensitivity for neurocranial traumatic CT lesions,
but the CCHR did not. The difference in sensitivities for neurocranial traumatic
CT findings between the 2 decision rules seems to be mainly due to the more
stringent use of the risk factor of external injury in the CCHR. In the NOC,
this risk factor comprises all external injuries above the clavicles, whereas
in the CCHR only external injury indicating a skull (base) fracture is considered
a risk factor for neurocranial traumatic CT findings. Specificities for neurocranial
traumatic CT findings and for neurosurgical intervention were low for the
NOC decision rule, and higher for the CCHR but at the cost of a lower sensitivity
for traumatic findings on the CT scan.
A single-center prospective study by Ibanez et al17 included
1101 patients and validated several guidelines and decision rules for minor
head injury, including the CCHR and NOC. In this study, as well as in our
study, none of the guidelines or decision rules reached a 100% sensitivity
for traumatic lesions on the CT scan, with the NOC also reaching a higher
sensitivity (95%) than the CCHR (86%). Unfortunately, Ibanez et al17 reported only sensitivities for relevant acute intracranial
CT lesions and not the sensitivities for neurosurgical intervention. Furthermore,
it is not clear from the article how the decision rules were validated, especially
since that study population was not the same as the patient populations for
which these guidelines and decision rules were designed.
The incidence of traumatic CT findings (9.8%) and of subsequent neurosurgical
intervention (0.5%) in our study population correspond with findings in previous
studies of patients with minor head injury (traumatic findings, 6.4%-21.0%;
and neurosurgical intervention, 0.4%-1.0%).3,7,8 Assault
as the most common mechanism of injury is remarkable and may be due to the
fact that 2 of our participating centers are in 2 large cities in the Netherlands,
where crime rates are highest. Another reason may be that we included patients
with minor head injury irrespective of loss of consciousness. Assault usually
results in less severe injury than motor vehicle crashes or falls, which are
the more common mechanisms of injury in similar studies.3
In our adaptation of the NOC and CCHR decision rules for use in our
population, we did not include loss of consciousness as a risk factor, although
loss of consciousness is generally regarded as a risk factor for complications
after minor head injury. Loss of consciousness is often considered such a
strong predictor that its presence usually is considered an obligatory part
of the definition of minor head injury. The absence of loss of consciousness,
however, does not exclude the possibility of neurocranial lesions, some of
which may require neurosurgical intervention, although with a lower incidence
than when the patient has lost consciousness.17 Our
results emphasize this point, since almost 30% of patients requiring neurosurgical
intervention had not lost consciousness. Clearly, certain patients without
a history of loss of consciousness after minor head injury are also at risk
of serious complications and therefore require a CT scan. By not including
loss of consciousness as a risk factor in the adapted NOC and CCHR decision
rules and validating them as such, the reported sensitivities and specificities
of the adapted decision rules are valid for any patient with minor head injury,
irrespective of whether loss of consciousness was present. Our simple adaptation
to the 2 published decision rules may not be the optimal strategy, but it
was beyond the scope of our study to design an entirely new decision rule.
Designing a new decision rule, which is also applicable to patients with minor
head injury but without loss of consciousness, may however be better than
these simple adaptations to existing decision rules, and will require further
A limitation of our study is that we did not use the exact predictors
that Stiell et al3 defined in the derivation
of the CCHR. In that study, Stiell et al3 found
that a GCS score of less than 15 at 2 hours after presentation to the emergency
department was a risk factor for clinically important brain injury and neurosurgical
intervention. In our participating centers, however, most patients underwent
CT scanning within 2 hours of presentation. Therefore, we evaluated GCS at
1 hour after presentation instead of after 2 hours. Another predictor for
clinically important brain injury according to the CCHR is amnesia preceding
the traumatic event (retrograde amnesia) of more than 30 minutes. Our neurologists
found it difficult to assess the duration of retrograde amnesia, which makes
it an unreliable risk factor. Estimation of posttraumatic or anterograde amnesia
is easier and seems to be more reliable. Since posttraumatic amnesia was also
significantly associated with brain injury in the study by Stiell et al,3 we chose to use posttraumatic amnesia of more than
30 minutes as a risk factor instead of retrograde amnesia. In addition, the
CCHR defined vomiting as involving more than 1 episode of emesis, whereas
we defined vomiting as any period of emesis. It seems unlikely that the low
sensitivity of the CCHR for traumatic lesions is due to our slight adjustments
to the decision rule. If anything, the contrary is more likely since our adjusted
predictors regarding the GCS score and vomiting are less restrictive than
the CCHR original predictors.
Another limitation is that data on patient history and examination,
although documented before the CT scan, were not always entered into the database
before the CT scan was performed in those cases when data entry before the
CT scan would have interfered with patient management. This may have caused
some classification bias. In addition, we did not exclude patients who presented
with minor head injury after a seizure and whose physical and neurological
examination postictally is difficult to interpret. There is also a theoretical
possibility that we may have missed patients undergoing neurosurgical intervention,
who were initially discharged from 1 of the participating hospitals, and who
later deteriorated and underwent emergency neurosurgical intervention in a
different hospital. This is a highly unlikely event since the centers participating
in our study are primary regional neurosurgical centers, which would mean
that patients who would present to a different hospital than 1 of our participating
centers would very likely be transferred to the participating center for neurosurgical
Despite these limitations, we were able to validate 2 published decision
rules for the indications for CT scanning in patients with minor head injury
in a large study population and multicenter setting. The NOC, both in its
original form and adjusted for use in our entire patient population, reached
the highest sensitivity for identifying patients with neurocranial traumatic
lesions, but since its specificity was very low, the potential reduction in
CT scans by implementing this rule would be much lower than estimated by Haydel
et al (3% vs 22%).7 The potential reduction
in CT scans by using the adapted CCHR decision rule in the entire patient
population may be considerable (37%). However, the adapted CCHR attained a
sensitivity for traumatic CT findings of only 83% to 87%, which may be too
low for clinical practice, although the sensitivity for neurosurgical intervention
A key clinical question is whether 100% sensitivity is needed for identifying
patients with any neurocranial traumatic CT finding.
The reason to perform an emergency CT scan in patients with minor head injury
is to detect intracranial complications of minor head injury that require
neurosurgical intervention or that cause significant clinical problems for
which close clinical observation is needed. For this reason, we also validated
the decision rules for clinically important lesions, which generally require
Still, the question remains whether all of the patients with a clinically
important lesion on the CT scan really did require observation and, consequently,
whether a CT scan was really indicated. A CT scan is certainly indicated in
patients with traumatic lesions requiring neurosurgical intervention; however,
we feel that focusing solely on neurosurgical intervention may be too restrictive.
We therefore think it would also be important to assess the outcomes in terms
of costs and effectiveness of head injury to identify those patients who may
benefit from an emergency CT scan.18 In this
respect, it is important to recognize that if the CT scan is negative and
the patient may then be sent home without further clinical observation, this
would result in both a gain in effectiveness (less days in hospital for the
patient) as well as in cost-savings both for the health care system and society
(a CT scan costs less than hospital admission).19 The
magnitude of these effects will need to be ascertained, which can then be
used to determine the optimal trade-off between sensitivity and specificity,
and may help to formulate an evidence-based approach for reducing CT scans
in patients with minor head injury.
In summary, based on application of the CCHR and the NOC in 3181 patients,
the adapted NOC decision rule appears valid for use in all patients with minor
head injury who are 16 years or older and have a GCS score of 13 to 15, irrespective
of loss of consciousness. However, the potential reduction in CT scans performed
for this indication is extremely low in the clinical context studied. The
adapted CCHR has a lower sensitivity for traumatic findings on the CT scan,
but would identify all patients requiring neurosurgical intervention. Further
research is needed to identify patients with neurocranial injury who do not
require neurosurgical intervention but may benefit from emergency CT scanning
and to determine the optimal trade-off between sensitivity and specificity
for a decision rule for CT scanning in patients with minor head injury based
on cost and effectiveness outcomes.
Corresponding Author: M. G. Myriam Hunink,
MD, PhD, Departments of Radiology and Epidemiology and Biostatistics, Erasmus
MC–University Medical Centre, PO Box 1738, 3000 DR Rotterdam, the Netherlands
Author Contributions: Dr Hunink had full access
to all of the data in the study and takes responsibility for the integrity
of the data and the accuracy of the data analysis.
Study concept and design: Smits, Dippel, Hunink.
Acquisition of data: Smits, Dippel, Haan, Dekker,
Vos, Kool, Nederkoorn, Hofman, Twijnstra, Tanghe.
Analysis and interpretation of data: Smits,
Drafting of the manuscript: Smits, Dippel,
Critical revision of the manuscript for important
intellectual content: Smits, Dippel, Haan, Dekker, Vos, Kool, Nederkoorn,
Hofman, Twijnstra, Tanghe, Hunink.
Statistical analysis: Smits, Dippel.
Obtained funding: Hunink.
Administrative, technical, or material support:
Smits, Dippel, Haan, Dekker, Vos, Kool, Nederkoorn, Hofman, Twijnstra, Tanghe,
Study supervision: Dippel, Hunink.
Financial Disclosures: None reported.
Funding/Support: This study was supported by
grant VAZ 01-104 from College voor Zorgverzekeringen.
Role of the Sponsor: The authors’ work
was independent of College voor Zorgverzekeringen. College voor Zorgverzekeringen
had no involvement in the study design, data collection and analysis, writing
of the manuscript, or in the decision to submit this article for publication.
Acknowledgment: We thank Jolanda Brauer, RN,
Department of Neurology at University Medical Center Nijmegen St. Radboud,
as well as Wibeke J. van Leeuwen, RN, Caroline H. van Bavel-van Hamburg, RN,
and Belinda Tara-Prins, RN, Department of Radiology at Erasmus Medical Center,
for their invaluable contribution to patient data collection. Their work was
funded solely by College voor Zorgverzekeringe and the medical centers involved
in the study.