Head movement during CT brain perfusion acquisition of patients with suspected acute ischemic stroke
Introduction
Stroke is the 3rd most common cause of death and ranks second after ischemic heart disease as a cause of lost disability-adjusted life-years in the western world [1], [2]. CT Brain Perfusion imaging (CTP) is a promising diagnostic tool for initial evaluation of acute ischemic stroke patients [3], [4], [5] and has been validated in some previous study [6], [7], [8], [9]. With CTP analysis, areas with brain perfusion defects can be detected after the onset of clinical symptoms, which allows the differentiation between the irreversibly damaged infarct core and the potentially reversibly damaged infarct penumbra [10], [11]. This information is important in choosing the most suitable therapy [12].
During CTP acquisition, CTP source images are acquired every 1–3 s for approximately 1 min. Time–attenuation curves of individual voxels in these images are used to estimate local perfusion parameters such as cerebral blood volume, cerebral blood flow, and mean transit time. Using pre-defined thresholds and contra-lateral comparison, these maps are combined to create a summary map estimating the volume of infarct core and penumbra [3], [13]. In the analysis, it is assumed that a certain position in the CTP source images is associated with a single anatomical position in each time frame. In clinical practice, this assumption may not hold due to the patient's head movement during the image acquisition.
Several approaches for reduction of head movement during image acquisition have been proposed. The most straight-forward method is to use a head restraint. Acceptable methods for use in human studies are foam headrest, molded plastic masks, tapes, orthopedic collars and straps, and vacuum-lock bags [14], [15]. However, such methods are not able to eliminate movement entirely. The more restrictive methods may be uncomfortable, reducing their acceptability by patients and potentially even giving rise to further movement to relieve discomfort [16]. From Positron Emission Tomography (PET) studies it is known that even with headrests sudden or gradual head movements are frequently observed during image acquisition [14], [17].
Head movement during CTP image acquisition has been recognized as a source of inaccuracy in cerebral blood flow measurements [15], [18]. CTP analysis software packages are usually capable of correcting for small head movements, but in our experience this correction is often not sufficient. Fig. 1 shows an example of the impact of head movement on the perfusion parameters generated from a CTP dataset, where the time-Minimum Intensity Projection (t-MIP) image shows a double falx cerebri and perfusion maps show a frontal left shadow with high Cerebral Blood Volume (CBV) and Cerebral Blood Flow (CBF) values. In current practice, time frames within a CTP dataset with excessive movement are commonly considered unusable and are excluded from analysis. This results in a reduction of information and an increase of uncertainties in the perfusion parameter estimation. The decision to remove these time frames is currently based on subjective interpretation of radiologists or technicians.
Up to now, head movement has not yet been studied quantitatively. The goal of this study is to analyze and quantify the extent, frequency and severity of head movement during CTP acquisition in a population of patients suspected of acute ischemic stroke. Furthermore, we studied the relation between the severity of head movement with the neurological condition of patients at admission, as expressed by the National Institute of Health Stroke Scale (NIHSS) score and with the baseline characteristics: age and gender.
Section snippets
Patient population
We retrospectively included all patients admitted to our medical center between January 2010 and February 2012, who were suspected of acute ischemic stroke and underwent CTP. Non-contrast CT (ncCT) was performed on all patients suspected of ischemic stroke. If intracranial hemorrhage was ruled out, CTP was performed. Exclusion criteria for this study were: patients with previous craniotomy and patients with poor cardiac function. A flow diagram to sum up patient population is shown in Fig. 2.
Results
A total of 220 CTP datasets of 103 patients were included. For most patients (89/103), the CTP study consisted of two CTP series at two brain levels. For 14 patients, CTP data were only available for one series at a single level. We also included 15 follow-up CTP study available (13 patients with two series, 2 patients with only one). Sixty-five patients (62.5%) were male. The average age was 62 years, ranging from 19 to 90 years. Detail of patient's characteristic is listed in Table 1.
Discussion
In this study we have shown that in patients with acute ischemic stroke, moderate and severe head movement during CTP acquisition is rather common. In our population of 103 patients who presented with a suspicion of ischemic stroke, 24% had at least one CTP dataset showing moderate to severe head movement. Since CTP analysis assumes that a specific location in each time frame is associated with a single anatomical position, movement of the head alters time-attenuation curves and as such CTP
Conclusion
We have shown that head movement during CTP acquisition is common in our population of patients with acute ischemic stroke. Motion occurs during the whole acquisition period and is independent of the neurological condition. Almost a quarter of all patients showed moderate or severe head movement during CTP acquisition and therefore the CTP dataset was considered unsuitable for accurate CTP analysis. We presented a technique to quantify head movement with a good correlation with the qualitative
Conflict of interest
All authors declare that there is no potential conflict of interest including any financial, personal or other relationships with other people or organizations within three (3) years of beginning the work submitted that could inappropriately influence (bias) the work.
Acknowledgements
This work has been supported by LP3M University of Sumatera Utara and USU Academic Hospital through Directorate General of Higher Education (DIKTI) Scholarship, Ministry of National Education, Indonesia.
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Academic Medical Center (AMC), Department of Radiology, GI-233, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Tel.: +31 20 5663304; fax: +31 20 6917233.
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Academic Medical Center (AMC), Department of Biomedical Engineering and Physics, L0-105, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Tel.: +31 20 5665191; fax: +31 20 6917233.
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Academic Medical Center (AMC), Department of Biomedical Engineering and Physics, L0-147, Meibergdreef 9, 1105 AZ Amsterdam, The Netherland. Tel.: +31 20 5665189; fax: +31 20 6917233.
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Academic Medical Center (AMC), Department of Neurology, H2-214, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Tel.: +31 20 5664045; fax: +31 20 6917233.
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Academic Medical Center (AMC), Department of Biomedical Engineering and Physics, L0-120, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Tel.: +31 20 5665023; fax: +31 20 6917233.
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Academic Medical Center (AMC), Department of Biomedical Engineering and Physics, L0-106, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands. Tel.: +31 20 5665182; fax: +31 20 6917233.