|Year : 2014 | Volume
| Issue : 4 | Page : 752-757
Role of magnetic resonant diffusion-weighted imaging in evaluation of acute cerebral stroke
Mohamed Ahmed El-Brashy MSc , Hala Hafez Mohamed, Osama Mohamed Ebied
Department of Radiodiagnosis, Faculty of Medicine, Menoufia University, Menufia, Egypt
|Date of Submission||29-Sep-2013|
|Date of Acceptance||02-Dec-2013|
|Date of Web Publication||22-Jan-2015|
Mohamed Ahmed El-Brashy
3 Abd El-Hamid Lotfy Street, Madent Nasr, Cairo
Source of Support: None, Conflict of Interest: None
This study aimed to show the role of diffusion-weighted MRI (DWI) in the diagnosis of acute stroke.
DWI is highly sensitive in detecting early cerebral ischemic changes in acute stroke patients. In this study, we compared the role of DWI with that of conventional MRI techniques. Furthermore, we compared the size of ischemic lesions on DWI scans with the fluid-attenuated inversion recovery (FLAIR) images.
Materials and methods
We performed T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), FLAIR, and DWI MRI in 30 patients who presented with acute stroke. T1WI, T2WI, FLAIR, and DWI were performed for all patients and an apparent diffusion coefficient map on only 10 patients. The size of ischemic lesions was measured on DWI and FLAIR images.
With DWI, 100% of the ischemic lesions were detected, with FLAIR recovery 83% were detected, whereas with T1-weighted and T2-weighted images, only 63% of lesions were identified. The size of the lesion on DWI scans was larger than the FLAIR images, particularly in patients examined within the first 6 h of stroke onset.
DWI is more sensitive than conventional MRI in detecting early ischemic lesions in acute stroke patients. The size of the lesions measured on DWI and FLAIR images in the first 6 h was larger than those measured between 6 h and 3 days. MRI is recommended strongly for the accurate diagnosis of acute stroke.
Keywords: Acute stroke, diffusion-weighted MRI, fluid-attenuated inversion recovery, T1-weighted imaging, T2-weighted imaging
|How to cite this article:|
El-Brashy MA, Mohamed HH, Ebied OM. Role of magnetic resonant diffusion-weighted imaging in evaluation of acute cerebral stroke. Menoufia Med J 2014;27:752-7
|How to cite this URL:|
El-Brashy MA, Mohamed HH, Ebied OM. Role of magnetic resonant diffusion-weighted imaging in evaluation of acute cerebral stroke. Menoufia Med J [serial online] 2014 [cited 2020 Feb 23];27:752-7. Available from: http://www.mmj.eg.net/text.asp?2014/27/4/752/149744
| Introduction|| |
Stroke is a leading cause of death and is a major cause of long-term disability .
Stroke is an injury to the central nervous system that is characteristically abrupt in onset and because of a vascular insult. The term is reflective of damage to the brain secondary to ischemia or hemorrhage. It is the third cause of mortality and the first cause of disability in adults in the USA. Strokes are ischemic ~80% of the time, and until recently, there was no beneficial intervention available .
Diffusion-weighted MRI (DWI) provides potentially unique information on the viability of brain tissue. It provides image contrast that is dependent on the molecular motion of water, which may be altered markedly by disease. The method was introduced into clinical practice in the mid-1990s .
The primary application of DWI has been in brain imaging, mainly because of its high sensitivity to ischemic stroke - a common condition that appears in the differential diagnosis in almost all patients who present with a neurologic complaint .
DWI has shown great promise in the diagnosis of acute stroke .
| Patients and methods|| |
The study was carried out on 30 patients, 21 men and nine women, age range between 44 and 65 years. They presented with one or more of the neurological manifestations suggestive of cerebrovascular stroke.
Patients were assessed clinically in the emergency room and/or neurology and neurosurgery departments, and were referred to the radiodiagnosis department for MRI examination of the brain.
The mean time between the onset of symptoms and the MRI investigation was 16 h (range 2-50 h). Seven patients were imaged in the hyperacute stage (<6 h after onset) and 23 patients were imaged between 6 and 50 h after the onset of symptoms [Table 1].
Method of examination
MRI scans were performed using a 1.5 T ecoplaner imaging-equipped whole body scanner (General Electric Medical System) according to a protocol optimized to obtain high quality as rapidly as possible in ill and potentially uncooperative patients.
Axial T1-weighted imaging (T1WI), axial T2-weighted imaging (T2WI), axial fluid-attenuated inversion recovery technique (FLAIR), and axial DWI were performed in all 30 patients. Axial apparent diffusion coefficient (ADC map) was assessed only in 10 patients.
Preparation of patients
There was no special preparation of patients who underwent the MRI examination. None had any contraindication to the study.
Three planes localizer, axial (T1WI), axial (T2WI), axial (FLAIR), axial DWI, axial (ADC map).
The patient lay supine with the head first in the gantry using a head coil. The three-plane localizer (scout) includes axial, coronal, and sagittal images, matrix size 384 × 224 ms, slice thickness 6 mm, interslice gap 2 mm, and field of view 26 × 26.
Axial T1WI, echo time (TE): 15 ms. Repetition time (TR): 480 ms. Axial T2WI, TE: 133 ms, TR: 8000 ms. Axial FLAIR, TE: 91 ms, TR: 3900 ms. Inversion time = 2000 ms. Axial DWI, TE: 112 ms, TR: 6300 ms. Axial ADC map: is diffusion postprocessing. B-value: 1000 s/mm 2 . Time of sequences [Table 2].
All the image sequences were reported carefully to identify any signal abnormalities. The size of the lesions was measured as length × width in cm.
| Results|| |
We analyzed the results of 30 patients, 21 men and nine women, mean age 52 years and range 44-65 years; they presented with signs and symptoms suggestive of acute stroke such as hemiplegia (19), numbness (20), disturbed level of consciousness (eight), ataxia (four), and blurring of vision (one). The mean time between the onset of symptoms and the MRI investigation was 16 h (range 2-50 h). Seven patients were imaged in the hyperacute stage (<6 h after onset) and 23 patients were imaged in the acute stage between 6 and 50 h after the onset of symptoms.
Hyperintense signals on T1WI, T2WI, FLAIR, and DWI and hypointense signals on the ADC map indicate the presence of cerebral infarction [Figure 1] and [Figure 2].
|Figure 1: Hyperintense signal on T2, FLAIR, and DWI observed at the left temporal and occipital region. DWI, diffusion-weighted MRI; FLAIR, fluid-attenuated inversion recovery.|
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|Figure 2: DWI showed a hyperintense signal and hypointense signal on the ADC map seen at the left deep temporal region close to the temporal horn of the lateral ventricle. ADC, apparent diffusion coefficient; DWI, diffusion-weighted MRI.|
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Conventional T1W1 and T2WI detected infarctions in 19/30 patients (63%) and FLAIR detected infarctions in 25/30 patients (83%). DWI showed the highest sensitivity as it identified the lesions in all 30 patients. Hypointense lesions were detected in all the patients who were assessed by the ADC map.
The size of the lesions was measured on DWI and FLAIR scans; seven patients were imaged within 6 h of stroke onset [Table 3] and 18 patients were imaged from 6 h to 3 days after the onset of stroke [Table 4]. The mean lesion size (length × width) in cm was larger on the DWI scans (2.7 × 1.8 cm) than on FLAIR images (2.6 × 1.7 cm). In patients who were imaged within 6 h after stroke, the difference in the mean lesion size on the DWI scans (3.48 × 2.5 cm) and FLAIR images (3.05 × 2.01 cm) appeared to be even more profound than in patients who were imaged between 6 h and 3 days on the DWI (2.51 × 1.8 cm) and FLAIR images (2.4 × 1.5 cm).
|Table 3: Mean size (length × width) of the infarctions detected within the first 6 h of stroke onset as seen on FLAIR and DWI|
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|Table 4: Mean size (length × width)of the infarction detected between 6 h and 3 days from the onset of stroke on FLAIR and DWI|
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| Discussion|| |
Our study included 21 men and nine women, mean age 52 years, ranging from 44 to 65 years. A higher incidence of acute stroke was found among men than women. The study by Evan Everdingen et al. on 25 men and 17 women and the study by Roquer et al.  on 809 men and 772 women reported results that were in agreement with ours, that men are more prone to acute stroke probably because of overstress, smoking, and peripheral vascular disease, which are more common in men than women.
The mean time between the onset of symptoms and the early MR investigations in our study was 16 h (range from 2-50 h). Seven patients were imaged in the hyperacute stage (<6 h after onset); 23 patients were imaged between 6 and 50 h after the onset of symptoms. In the study by Lansberg et al. , the baseline MRI scan was performed at a mean of 29 ± 15 h after the onset of symptoms. Overall, 5/49 patients underwent scanning within 12 h after the onset of symptoms. In the study by Nakamuraa et al. , the interval between stroke onset and MRI examination ranged from 2 h to 8 days.
A study by Huang et al.  included 70 patients with cerebral infarction. The results showed that eight hyperacute cerebral ischemic infarctions were diagnosed by DWIs and ADC maps, but not detected by T2WIs. This shows that DWI and the ADC map have greater sensitivity for acute, especially hyperacute cerebral infarction than T2WI.
The study by Abdul Sattar et al.  reported that in 117 patients, the DWI was more sensitive than FLAIR in the detection of stroke during the first 6 h; it was still superior to FLAIR even after 24 h. In the hyperacute period after stroke, FLAIR could detect only 29% of the acute ischemic strokes that were identified by DWI.
The study by Thomalla  on 120 patients examined by DWI and FLAIR within 6 h of symptom onset showed a 'mismatch' between DWI and FLAIR as the acute ischemic lesions were visible on DWI, but not on FLAIR; this mismatch indicated lesions within less than 3 h. FLAIR imaging proved even superior to T2WI in the detection of ischemic lesions.
The study by Schaefer et al.  reported that computed tomography and MRI cannot reliably detect infarction at early onset. DW images are very sensitive and speciﬁc for the detection of hyperacute and acute infarctions. The study also reported that the majority of stroke lesions increase in volume on DW images, with the maximum volume achieved after 2-3 days.
Our results are in agreement that DWI and the ADC map are useful imaging methods to detect ischemic lesions in the hyperacute (>6 h after onset) and acute stage (6 h to 3 days after onset) of stroke. All the infarcts, 30/30 (100%), were found to be hyperintense on DWI and hypointense in the ADC map [Figure 3]. The final clinical diagnosis of these patients was acute cerebral stroke. Of 30 patients who underwent conventional MRI in hyperacute and acute stages, only 19 patients (63%) were diagnosed with cerebral infarcts [Figure 4],[Figure 5] and [Figure 6]. FLAIR imaging could diagnose 25 cases of infarcts (83%) [Figure 7]. Although less accurate than DWI, FLAIR imaging provided better results in detecting ischemic lesions than conventional MRI.
|Figure 3: Right high parietal acute infarction detected in DWI and the ADC map. A 55-year-old male patient presented to the neurology clinic with gradual weakness of the left upper and lower limbs. Axial T1WI and T2WI were insignificant: (a) a bright signal lesion at the right high parietal region (arrow) and (b) low signal lesion of the same site (arrow). ADC, apparent diffusion coefficient; DWI, diffusion-weighted MRI; T1WI, T1-weighted imaging; T2WI, T2-weighted imaging.|
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In terms of the size of the lesions, they were larger on DWI scans than on FLAIR images. In patients who were imaged within 6 h after cerebral stroke, the difference in the size of lesion on the DW images scans and FLAIR images appeared to be even more profound than in patients who were imaged between 6 h and 3 days. Our results are in agreement with the study by Evan Everdingen et al.  and Schaefer et al. .
|Figure 4: Right temporal acute infarction detected in T2WI, FLAIR, DWI, and ADC map of a 52-year-old male patient with acute onset of left-side hemiparesis. MR images were obtained 10 h after the onset of symptoms. (a-c) A bright signal lesion at the lateral part of the right temporal region(arrows), (d) a low signal at the same site (arrows). ADC, apparent diffusion coefficient; DWI, diffusion-weighted MRI; FLAIR, fluid-attenuated inversion recovery; T2WI, T2-weighted imaging.|
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|Figure 5: Left temporal acute infarction detected in T2WI, FLAIR, DWI, and the ADC map. Acute onset of right-sided hemiparesis in a 52-year-old man. MR images were obtained 10 h after the onset of symptoms. (a-c) A bright signal lesion at the lateral part of the left temporal region(arrows) and (d) a low signal at the same site. (arrows). ADC, apparent diffusion coefficient; DWI, diffusion-weighted MRI; FLAIR, fluid-attenuated inversion recovery; T2WI, T2-weighted imaging.|
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|Figure 6: Right caudate nucleus acute infarction detected in T2WI, FLAIR, DWI, and ADC map. MR study of a 58-year-old woman carried out 6 h after the onset of sudden weakness of the left upper and lower limbs. (a) A low signal lesion at the right caudate nucleus (arrows), (c-d) a bright signal at the same site (arrows). ADC, apparent diffusion coefficient; DWI, diffusion-weighted MRI; FLAIR, fluid-attenuated inversion recovery; T2WI, T2-weighted imaging.|
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|Figure 7: Right cerebellar hemisphere acute infarction detected in FLAIR and DWI of a 48-year-old female patient who presented with ataxia and blurring of vision 10 h before MRI examination. Axial T1WI and T2WI were insignificant, showing no abnormalities. (a) A fairly hyperintense lesion at the right cerebellar hemisphere (arrow) (b) the same lesion, but with a higher signal intensity (arrow). DWI, diffusion-weighted MRI; FLAIR, fluid-attenuated inversion recovery; T1WI, T1-weighted imaging; T2WI, T2-weighted imaging.|
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DWI allows the detection of acute ischemic lesions within minutes, but does not allow any further conclusions on lesion age during the initial hours of stroke. T2 signal changes might allow further timely allocation of ischemic lesions as ischemic lesions become visible on T2WI within the first hours of stroke onset .
High signal intensity may be observed on T2WI and PD images beginning ~8 h after onset corresponding to a vascular distribution. T1WI may take significantly longer to show a low signal. FLAIR images show an abnormal signal sooner than T2WI and have been shown to be useful in detecting infarcts within 3 h after the onset of acute stroke, whereas ischemic lesions show a high signal of DWI and a low signal on ADC maps within minutes .
The DWI technique is the only brain imaging method to reliably show ischemic parenchymal injury within the first minutes to hours after the onset of stroke. Ischemiainduced membrane dysfunction and cytotoxic edema restrict the diffusion of water and lead to a decrease in the ADC, a physiological measure of the rate of water movement through brain parenchyma. As a result, acute focal ischemia is hyperintense on DWI scans and hypointense on ADC maps. On FLAIR sequences, early blood-brain barrier disruption in stroke appears as delayed gadolinium enhancement of hemispheric sulci. Acute ischemic stroke produces no signs on FLAIR in the first 6 h from onset, with areas of hyperintensity evolving thereafter. A DWI lesion without a matching hyperintensity on FLAIR suggests that the stroke occurred in less than 6 h .
The ADC map can also discriminate between a chronic infarct that appears hyperintense on T2WI as well as on DWI despite the lack of restricted diffusion, the phenomenon referred to as 'T2 shine-through' .
| Conclusion|| |
MRI is an efficient examination that can rapidly diagnose stroke and therefore provide better management for the patient.
In the hyperacute and acute stages, the ischemic lesions appear hyperintense on DWI and hypointense on the ADC map.
DWI showed considerable superiority in detecting acute ischemic lesions than T1WI, T2WI, and FLAIR. DWI and the ADC map are useful techniques in detecting ischemic lesions at different stages. However, FLAIR is superior to T1WI and T2WI in acute stroke.
The size of the lesions in patients who were imaged within 6 h after the onset of cerebral stroke was larger on DWI scans than on FLAIR images, but there was no significant difference in patients who were imaged between 6 h and 3 days from onset.
MRI is strongly recommended for the accurate diagnosis of acute stroke.
| Acknowledgements|| |
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3], [Table 4]