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Research Article | Volume 14 Issue: 4 (Jul-Aug, 2024) | Pages 933 - 937
Role Of Susceptibility Weighted Magnetic Resonance Imaging in The Evaluation of Acute Ischemic Stroke
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1
1Associate Professor department of Radiology Subbaiah institute of medical sciences Shivamogga. India
2
2Associate Professor department of Radiology Subbaiah institute of medical sciences Shivamogga. India
3
3Associate Professor department of Radiology Subbaiah institute of medical sciences Shivamogga. India
4
Professor department of Radiology Subbaiah institute of medical sciences Shivamogga. India
Under a Creative Commons license
Open Access
Received
July 10, 2024
Revised
July 15, 2024
Accepted
Aug. 12, 2024
Published
Aug. 28, 2024
Abstract

Background: "Stroke" is a generic term meaning sudden onset of a neurologic event and is also called cerebrovascular accident or "brain attack". It is one of the leading causes of death globally and is a significant cause of long-term disability. Magnetic resonance imaging (MRI) provides critical information in acute stroke that can be used to confirm the diagnosis and direct both acute therapeutic interventions and long-term treatment decisions. MRI can identify regions of hemorrhage, active ischemia, and vessel occlusion. This has made SWI a powerful technique in the evaluation of stroke patients. Materials and Methods: This is a Cross-sectional study was done in the Radiology Department, Subbaiah Institute of Medical Sciences over the period of 1 year. All clinically suspected patients with a neurological deficit (signs and symptoms like dysphasia/aphasia, hemiparalysis/hemiparesis, ataxia, convulsions) were referred by a neurologist, physicians for MRI brain in medical college and general hospital. Results: In this study, out of the 125patients, 115 patients (92%) had infarcts in the arterial territory, and 10 patients (8%) had venous infarcts. Hemorrhage was detected in 42 patients (33.6%), of which 33 cases were arterial infarcts and 9 were venous infarcts. Hemorrhage was seen in 27(35%) out of 77 male patients and 15 (31.2%) out of 48 female patients. Hypointense blooming was not seen in 83 patients (66.4%) in this study. Occlusion in TOF-MRA was seen in 25(21.7%) patients out of 115 patients. Susceptibility vessel sign is seen in 20 patients out of 25 patients showing occlusion in TOF-MRA. Loss of flow void on T2 indicating thrombus in the vessel was seen in 5 patients. Conclusion Susceptibility weighted imaging is superior than conventional MR imaging in the detection of haemorrhagic transformation of infarct. SWI can also detect the thromboemboli in the vessels by susceptibility vessel sign. SWI indicates the need for doing perfusion MRI to detect penumbra in cases of DWI-SWI mismatch

Keywords
INTRODUCTION

"Stroke" is a generic term meaning sudden onset of a neurologic event and is also called cerebrovascular accident or "brain attack". It is one of the leading causes of death globally and is a significant cause of long-term disability. [1] Cerebrovascular ischemia due to thromboembolism or atherosclerotic stenosis leads to acute infarct with or without hemorrhage. Magnetic resonance imaging (MRI) provides critical information in acute stroke that can be used to confirm the diagnosis and direct both acute therapeutic interventions and long term treatment decisions. [2] MRI can identify regions of hemorrhage, active ischemia, and vessel occlusion. [3]

 

Conventional MRI is insensitive to detect microbleeds and petechial hemorrhages in ischemic infarction. MRI can identify hemorrhage In ischemic infarct using susceptibility- weighted imaging. [4]

 

Susceptibility-weighted imaging (SWI) is a T2-weighted gradient-echo post-processing reconstruction technique that emphasizes the paramagnetic properties of blood products. [5] It is very sensitive for the detection of intravascular venous deoxygenated blood as well as extravascular blood products. It can also detect the probability of hemorrhagic transformation of an infarct before thrombolytic treatment, as well as localize the affected vascular territory. [6] This has made SWI a powerful technique in the evaluation of stroke patients.

METHODOLOGY

This is a Cross-sectional study was done in the Radiology Department, Subbaiah Institute of Medical Sciences over the period of 1 year.

 

Inclusion Criteria: -

  1. All ages and
  2. Patients with acute symptoms of stroke and in whom MR imaging is done within seven days showing restriction on Diffusion-weighted imaging (DWI)

 

Exclusion Criteria:

  1. Patients with causes of hemorrhage other than acute ischemic stroke-like cerebral amyloid angiopathy.
  2. Follow-up MR imaging of asymptomatic known cases of patients with stroke or chronic stroke
  3. Patients in whom MR imaging is clinically indicated but cannot be performed due to conditions like a cardiac pacemaker, cochlear implants, and other routine contraindications for MRI.

 

Source of data

All clinically suspected patients with a neurological deficit (signs and symptoms like dysphasia/aphasia, hemiparalysis/hemiparesis, ataxia, convulsions) were referred by a neurologist, physicians for MRI brain in medical college and general hospital.

Sample size 125 patients.

 

Methodology:

All clinically suspected patients with neurological deficits were referred by neurologists, physicians for MRI of the brain in medical college and general hospital.

 

Equipment

The machine used in this study was a 1.5 Tesla MRI scanner (GE).

 

MRI Protocol

The following sequences were performed, sagittal T1 weighted images, axial T2 weighted images, Fluid attenuated inversion recovery (FLAIR), Diffusion-weighted imaging (DWI), including Apparent diffusion coefficient (ADC) and Susceptibility, weighted imaged (SWI).

 

The parameters were as follows:

  • T1 weighted Imaging: Time to Repeat (TR): 480ms, Time to echo(TE): 8.7 ms; slice thickness: 5mm; matrix size: 320x 80; FOV : 230 mm,
  • T2 Weighted Imaging: Time to Repeat (TR) : 5000ms, Time to echo(TE): 92 ms; slice thickness: 5mm; matrix size: 448x 70; FOV : 230 mm.,
  • FLAIR: TR: 9000ms; TE: 92 ms; slice thickness: 5 mm; matrix size: 256 x 85; FOV: 230 mm; Inversion time (T1): 2,500 ms; flip angle: 150 degrees
  • Diffusion – weighted image (DWI): Echo planar imaging (EPI) spin echo; Time to Repeat (TR): 3600 ms; Time to Echo (TE): 102 ms; slice thickness: 5 mm; matrix size: 192 x 100; FOV: 230 mm; and b values 0 and 1000 s/mm 2
  • SWI: TR:49 ms; TE: 40 ms; matrix size: 512x256, slice thickness is 2.1 mm; ; FOV: 220 mm; flip angle: 20 degrees, acquisition time: 2.58 min, bandwidth, 80 KHz,
  • Magnetic resonance angiography (MRA): Time to repeat (TR): 3.5 ms; TE;1.1 min; matrix size: 192 x 256, slice thickness: 1.0 mm; ; FOV: 270 mm; flip angle: 30 degrees.
  • Time –of-flight angiography (TOF MRA): TR: 36 ms; TE: 6.9 min; slice thickness: 1.4 mm; matrix size: 224 x 256; FOV: 18 cm; flip angle: 25 degrees.

 

Imaging protocol for SWI was TR – 48 ms, TE – 40 ms, flip angle (FA) – 15 degrees, slice thickness – 2.5 mm, interslice gap 0.5 mm, bandwidth – 80 kHz, and field of view (FOC) – 230 x 200 mm, matrix 256 x 192 mm, acquisition time 3 minutes 29 seconds. Four sets of images were generated and analyzed, including magnitude, phase, SWI, and minimum intensity projections.

Hypointense areas(blooming) in the infarct area on SWI was considered as hemorrhage. Hyperintense areas on the T1 weighted sequence, heterogeneous increased signal intensity in the infarct area on T2 and FLAIR was considered as hemorrhage.

 

‘Susceptibility sign’ is positive when the diameter of a hypointense vessel exceeds the diameter of the contralateral artery on Susceptibility – weighted imaging (SWI) images.

 

The following data was recorded – patient’s age, sex, clinical history, territory and type of infarct, the extent of infarct, presence or absence of hemorrhage in SWI along with the extent of hemorrhage, presence or absence of Susceptibility sign, presence of prominent cortical and/or intramedullary veins in the vicinity of the infarct,presence of diffusion susceptibility mismatch.

 

Statistical methods

Data were entered in Microsoft excel. All qualitative variables in the study, such as the presence of hypertension, diabetes mellitus, gender, etc., were expressed in terms of proportion. All quantitative variables were expressed in descriptive statistics such as the mean. Hemorrhagic foci in patients with acute ischaemic stroke by SWI versus conventional MRimaging (T1,T2, and FLAIR) were compared.Susceptibility vessel sign on SWI was compared with the occlusion in TOF-MRA, indicating thrombus.

The statistically significant P value is <0.05.

RESULT

Table No.1: Distribution of age and sex of the patients.

Age in years

Gender

Total

Female n (%)

Male n (%)

< 20

1(0.8)

0(0)

1(0.8)

20-29

2(1.6)

6(4.8)

8(6.4)

30-39

4(3.2)

6(4.8)

10(8)

40-49

3(2.4)

12(9.6)

15(12.0)

50-59

6(4.8)

11(8.8)

17(13.6)

60-69

15(12.0)

21(16.8)

36(28.8)

70-79

15(12.0)

17(13.6)

32(25.6)

>80

2(1.6)

4(3.2)

6(4.8)

Total

48(38.4)

77(61.6)

125

 

In this study, the peak incidence of neurological deficits in males occurred in the age group between 60-69 years ,i.e. ,21 patients(16.8%). In females, the peak incidence occurred in the age group between 60-69 years and 70-79 years, i.e,15 patients (12%) each.

 

Table No. 2: Number of arterial infarcts in the study.

Arterial Infarcts

Number (n)

Percentage (%)

Present

115

92

Absent

10

8

Total

125

100

 

Table No. 3: Number of venous infarcts in the study.

Venous Infarcts

Number (n)

Percentage (%)

Present

10

8

Absent

115

92

 

In this study, out of the 125patients, 115 patients (92%) had infarcts in the arterial territory, and 10 patients (8%) had venous infarcts

 

Table No 4: Territorial Distribution of arterial infarcts

Arterial Territory

Number (n)

Percentage (%)

MCA

61

52.5%

Vertebral-basilar

30

26%

ACA

6

5.1%

ACA-MCA

10

8.6%

MCA-PCA

8

6.8%

 

Table No. 5: Number of patients with hemorrhage in the study.

Hemorrhage

Number (n)

Percentage (%)

Absent

83

66.4

Present

42

33.6

Total

125

100

 

Hemorrhage was detected in 42 patients (33.6%), of which 33 cases were arterial infarcts and 9 were venous infarcts. Hemorrhage was seen in 27(35%) out of 77 male patients and 15 (31.2%) out of 48 female patients. Out of the 42 patients with hemorrhagic infarcts,20 patients (47.6%) had hypertension, and 10 patients (23.8%) had diabetes mellitus

 

Table No.6: Detection of hemorrhage by SWI

SWI

Number (n)

Percentage (%)

No Hemorrhage

83

66.4

Hemorrhage

42

33.6

Total

125

100

 

Susceptibility weighted imaging detected hypointense blooming in the areas of infarct in   42 (33.6%)                                   out of          125 patients. Hypointense blooming was not seen in 83  patients (66.4%) in this study.

 

Table No. 7: Number of patients with Susceptibility sign seen in the study.

Susceptibility Sign

Number (n)

Percentage (%)

Absent

105

84

Present

20

16

Total

125

100

 

Table no 8: Distribution of susceptibility sign:

Location

Number(n)

Percentage(%)

MCA

14

70

PCA

1

5

Vertebral artery

2

10

Venous sinuses

3

15

Total

20

100

 

Table No.9: Occlussion in TOF-MRA

Occlusion in TOF-MRA

Number(n)

Percentage(%)

Absent

90

78.3

Present

25

21.7

 

Occlusion in TOF-MRA was seen in 25(21.7%) patients out of 115 patients. Susceptibility vessel sign is seen in 20 patients out of 25 patients showing occlusion in TOF-MRA. Loss of flow void on T2 indicating thrombus in the vessel was seen in 5 patients

Table no.10: Distribution of Hypointense vessel sign.

Hypointense vessel sign

Number(n)

Percentage(%)

Present

35

30.4

Absent

80

69.6

Total

115

100

 

Out of 115 patients with arterial infarcts, hypointense vessel sign is seen in 35 (30.4%)  patients.

 

Table no.11: Number of cases with Diffusion-susceptibility mismatch

DWI-SWI mismatch

Number(n)

Percentage

Present

5

4.4

Absent

110

95.6

Total

115

100

 

Out of 115 cases of arterial infarcts, diffusion susceptibility mismatch indicating         penumbra was seen in 5(4.4%) patients

DISCUSSION

According to Sleiman et al [7] most of the strokes are arterial strokes, mainly ischemic, less often of hemorrhagic origin. Studies by Kim et al [7], Biswas et al. [8], Zarei et al. [9] reported the middle and carotid cerebral arteries as the most common involved arteries.

 

In a study by Assarzadegan et al [10], among the ischemic strokes, the stenosis in main cerebral arteries was seen in 709 (70.1%) patients, consisting of 488 MCA strokes, 208 PCA strokes, and 53 ACA strokes.In 59 and 182 patients, the vertebrobasilar and carotid arteries were respectively affected. Twenty-three cases had a watershed stroke, three suffered from a venous stroke, and lacunar stroke occurred in 35 of the cases.

 

In a Study by Ebrahimi et al., [11] the Posterior cerebral artery territory showed the highest degree of vascular stenosis. Posterior cerebral artery stenosis alone was observed in 51.3% of the cases; 27.4% of the cases suffered from anterior artery stenosis, and 21.6% had simultaneous anterior and posterior cerebral artery stenosis.

 

According to Semenov et al [11], venous infarct more often (63%) than an arterial (15%) infarct is accompanied by hemorrhage (primary or secondary in the early period), and a high risk of hemorrhage should be a contraindication to intravenous thrombolysis.

 

According to Feigin et al [13] ICH accounts for approximately 10-20% of all strokes. The incidence of ICH is substantially variable across countries and ethnicities.

The incidence of ICH increases with advanced age. [14] A recent inpatient database study from the Netherlands based on a retrospective cohort study reported that the incidence of ICH per 100,000 was 5.9 in 35-54 years, 37.2 in 55-74 years, and 176.3 in 75-94 years old in 2010. For all ages, the annual incidence rate per 100,000 persons was higher in men than in women; 5.9 vs. 5.1 in people aged 35-54 years, 37.2 vs. 26.4 in those aged 55-74 years, and 176.3 vs. 140.1 in those aged 75-94 years. [15] In a German study analyzing the database of a regional prospective stroke registry between 2007 and 2009, 34% of 3,448 patients with ICH were aged 80 years or more. [16]

 

According to the American stroke association, Hemorrhagic strokes make up about 13 percent of stroke cases. According to Grysiewicz et al [17] there is no difference between women and men as a risk factor in intracranial hemorrhage, except during pregnancy and postpartum.

 

In our study, out of the 125 patients, 115 patients (92%) had infarcts in the arterial territory, and 10 patients(8%) had venous infarcts. Arterial infarcts are more common than venous infarcts.

 

It was observed that out of the 115 arterial infarcts, 61 (52.5%) infarcts were present in the MCA territory, 30 (26%) in the vertebra- basilar territory, 6(5.1%) in the ACA territory, 10 (8.6%) in the ACA – MCA watershed territory and 8 (6.8%) in the MCA- PCA territory. Among arterial infarcts, the most commonly involved artery is MCA, followed by vertebra-basilar territory, ICA, and ACA.

 

Out of the 61 infarcts in the MCA territory, 17 (27.8%) infarcts showed hemorrhage, 9 (30%) out of the 30 infarcts in the vertebra- basilar territory, 1(16.6%) infarct out of 6 infarcts in ACA territory,3 (30%) out of the 10 infarcts in the ACA- MCA watershed territory, 3 (37.5%) out of the 8 infarcts in the MCA-PCA watershed territory showed hemorrhages. Overall the hemorrhagic infarcts were more common in the supratentorial region than the infratentorial region.

 

Hemorrhage was detected in 42 (33.6%) patients, of which 33 cases were arterial infarcts and 9 were venous infarcts.90% of the venous infarcts showed hemorrhage, and 28.7% of the arterial infarcts showed hemorrhage. Venous infarcts are frequently hemorrhagic, and SWI helps in detecting even small hemorrhages in venous infarcts. In 

this study, nine venous infarcts with hemorrhage were detected, and SWI could detect hemorrhage in all cases.

 

Hemorrhage was seen in 27(35%) out of 77 male patients and 15(31.2%) out of 48 female patients. There is not much difference in gender in the hemorrhagic transformation of the infarct.

In this study, 45 patients had hypertension,36 patients had diabetes mellitus, and 23 patients had both hypertension and diabetes mellitus. Out of the 42 patients with hemorrhagic infarcts, 20 patients had hypertension, and 11 patients had diabetes mellitus. Hypertension – induced lipohyalinosis (consisting of subintimal deposition of lipid-rich hyaline material with disruption of muscle and elastic elements) has been preferentially linked to hematomas in the deep grey matter.

Intraarterial thrombolytic therapy has become a common treatment for acute ischemic stroke in tertiary care centers. But inherently, there is always a risk of hemorrhagic transformation following thrombolytic treatment. A blinded prospective randomized trial has confirmed that T2*GE images can detect hemorrhagic transformation within 6 hours after intraarterial thrombolytic therapy. Because SWI is sensitive to deoxyhemoglobin, SWI could detect hemorrhagic transformation within minutes after blood extravasation. Indeed, studies have shown that SWI can detect hemorrhagic transformation earlier than CT. [18]

 

There are only limited studies that have evaluated the utility of SWI in acute stroke patients. Most of the studies done so far had a small sample size in evaluating the usefulness of SWI. In fact, the present study may be the first study to assess the utility of SWI in more than 100 cases of acute infarct.

CONCLUSION

Susceptibility weighted imaging is superior than conventional MR imaging in the detection of haemorrhagic transformation of infarct. SWI can also detect the thromboemboli in the vessels by susceptibility vessel sign. SWI indicates the need for doing perfusion MRI to detect penumbra in cases of DWI-SWI mismatch.

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  10. Iadecola C, Bright and dark sides of nitric oxide in ischemic brain injury. TrendsNeurosci 1997:20:132-725.
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