The study was a cross-sectional study conducted in the Department of Radiodiagnosis, Agartala Government Medical College and GB Pant Hospital, Agartala, Tripura, India. The study period was from December 2018 to December 2020. Institutional Ethical Committee approval {Ref No. 4(6-11)-AGMC/Medical Education/Ethics Com/2018/1509} was obtained.

Inclusion and Exclusion criteria: All patients who were admitted within 24 hours of onset of symptoms in one unit of Medicine Department, were having signs of acute cerebral stroke and gave consent to participate were included in the study. Those who were found to have haemorrhagic stroke in initial CT scan, those having contraindication to MRI, pregnant women, those having multiple lesions and those denying consent were excluded. Thus, 70 patients were included in the study.

All the patients were examined using SIEMENS 128 slice CT- SOMATOM model definition AS and SIEMENS 3.0 Tesla MRI-SKYRA model. The typical signs of infarction e.g., parenchymal hypodensity, loss of grey- white differentiation, Dense MCA sign, Loss of insular ribbon sign were looked for in the CT scan. Then MRI was conducted using T1, T2, Fluid Attenuated Inversion Recovery (FLAIR), Diffusion-Weighted Imaging (DWI), Apparent Diffusion Coefficient (ADC), Magnetic Resonance Spectroscopy (MRS) and 3D Time of Flight (TOF). The technical parameters are given in [Table/Fig-1,2]. DWI was gold standard in diagnosis of ischaemic cerebral stroke. MRS data were evaluated to find out any change in the metabolite levels in the infarcted areas of brain. Time of flight data were evaluated to find out whether any change in the vessel architecture could be diagnosed.

This was performed using Statistical Package for the Social Sciences (SPSS) software version 25.0 (SPSS Inc, Chicago, USA). The sensitivity, specificity, Positive predictive value, negative predictive value and accuracy of NCCT brain were calculated (with 95% confidence interval, p-value).

The youngest patient in the study was of 18 years age and the oldest patient was 67 years of age. Age wise distribution of cases was depicted in [Table/Fig-3]. Male patients were 49 (70%) and female patients were 21 (30%) as shown in [Table/Fig-4].

Out of 70 patients 63 patients (90%) were found to have infarction, two patients (2.85%) were diagnosed to have a tumor and five patients (7.14%) were found to be normal. CT scan found out 55 cases out of 63 cases of infarction and missed 08 cases as shown in [Table/Fig-5]. Sensitivity of CT scan was 87.3% (p-value=0.002), specificity of CT scan was 71.4% (p-value=0.002), positive predictive value- 96.4% (p=0.002), negative predictive value was 38.4% (p-value=0.002), accuracy was 85.7% (p-value=0.002) as given in the [Table/Fig-6]. The p-values was determined using Chi-square test.

The MRS was performed in all patients of infarction (n=63) and findings were examined in two groups those presenting within six hours (n=15) and those within 06-24 hours (n=48). Creatinine was reduced in all cases, NAA was reduced in most of the cases (60% cases that presented within six hours and 89.6% cases that presented beyond six hours) [Table/Fig-7,8].

Results of TOF imaging showed narrowing in 33.34% cases and Thrombosis in 14.28% cases as incorporated in [Table/Fig-9]. A case of acute infarction involving Pons is shown in [Table/Fig-10], Left MCA territorial infarction in [Table/Fig-11], Posterior Cerebral Artery (PCA) territorial infarct in [Table/Fig-12], cases presenting prior to and after 6 hours with their MRS changes, respectively [Table/Fig-13,14].

[Table/Fig-10]:

Acute infarction involving left side of the pons: (a) Non Contrast Computed Tomography (NCCT) scan is normal; (b) T1WI shows very subtle hypointense signal intensity; (c) Fluid Attenuated Inversion Recovery (FLAIR) shows definite signal change; (d) Diffusion restriction in Diffusion-Weighted Imaging (DWI).

[Table/Fig-11]:

A case of acute left Middle Cerebral Artery (MCA) territorial infarct: (a) Narrowing of Left MCA in 3D Time of Flight (TOF); (b) Hyperintensity in Fluid Attenuated Inversion Recovery (FLAIR).

[Table/Fig-12]:

Acute Posterior Cerebral Artery (PCA) territorial infarct showing narrowing of right PCA in image: (a) and b) shows high signal intensity in FLAIR.

[Table/Fig-13]:

Acute infarction (<6 hours) case in right Middle Cerebral Artery (MCA) territory: (a) Normal metabolite profile on left side; (b) Raised choline, reduced creatinine and N-Acetylaspartate (NAA) with mild lactate peak in the involved area; (c) Infarction involving right occipital lobe.

[Table/Fig-14]:

Acute infarction involving left Middle cerebral artery (MCA) beyond 06 hours of onset: (a) No lactate peak in right side; (b) Lactate peak is seen on left side; (c) Hyperintensity in T2WI; (d) Diffusion restriction in Diffusion-Weighted Imaging (DWI) confirming the diagnosis.

In the study, it was observed that majority of the patients i.e., 38.6% were in the age group of 50-60 years and next common i.e., 31.4% of the patients were in the age group of above 60 years that presented with infarction. This correlates with the study of Andreassen UW et al., in which they have found that cerebral infarction was most commonly occurring in people above the age of 50 years (91.2% were ≥50 years) [11]. Forty four patients (69.84 %) out of all the infarction patients were male (Male: Female ratio was 2.31:1). This correlates with other studies Andreassen UW et al., Appelros P et al., [11,12]. In both these studies it was found that infarction was more common in males.

Sensitivity of CT scan was 87.3% (p-value=0.002), specificity of CT scan- 71.4% (p=.002), positive predictive value was 96.4% (p-value=0.002), negative predictive value 38.4% (p-value=0.002), accuracy of 85.7% (p-value=0.002). Lansberg MG et al., found that acute infarction was found by DWI in all instances whereas CT could diagnose 42-63% cases only [13]. Fiebach JB et al., opined that the sensitivity of infarct detection by the experts was significantly better when based on DWI (CT/DWI, 61/91%) [14]. Smajlović D and Sinanović O found that the CT scan in the first 12 hours of the stroke onset was positive in 32% of the patients [15].

As we can say from the study that creatine levels were reduced in infarct areas in all the cases irrespective of time since presentation. A raised choline level and reduced NAA level is seen in infarct areas in most of the patients. The increased choline values and reduced NAA values are more pronounced as the time increases. Further, we can see from the study that hyperacute stage of infarction (<6 hours) does not show any change in lactate levels whereas beyond 6 hours of presentation lactate levels are raised in significant number (83.3%) of cases. Saunders DE said that NAA and total Cr/PCr are reduced within the infarct compared to the contralateral hemisphere [16]. Gideon P et al., conducted a study of 08 patients of infarction where they found that a high lactate level was found in the acute phase [17]. Ramin SL et al., in their article mentioned that in case of acute infarction there is reduction in NAA level and slight increase in the Choline level [18]. They also mentioned in their article that Lactate is also raised in infarction. Mazibuko N et al., also found in their study that after infarction there is reduced NAA and creatinine level and increased choline and lactate level [19].

A 3D-TOF MR angiography was done to delineate the circle of Willies and arterial branches from it. Out of all the patients of infarction (n=63) TOF could demonstrate findings in only approx. 47.6 % of cases. Out of all the patients with positive TOF findings (n=30), 21 cases (33.34%) was of arterial narrowing (Stenosis) and 09 cases (14.28 %) were such where thrombosis could be found. Among the cases of arterial narrowing most cases were involving the MCA territory i.e., 61.9%, (n=13), whereas least commonly involved arterial territory was MCA-ACA territory {4.7%, (n=1)}. All of the cases where thrombosis was found were involving the MCA (n=09). Ojha R et al., where they found MCA was the most common artery to be stenosed in patients with ischaemic stroke (27.6 %) [20]. Radbruch A et al., in their study found that sensitivity for detection of embolic occlusion within M2/M3 was significantly different 84% for SWI versus 39% for TOF-angiography [21]. Further study can be performed in comparing the different aspect of MRS in relation to acute infarction and their relation to time.

The study was a hospital based study involving only one tertiary hospital. Therefore, the demographic profiles in the present study may not be representative of actual distribution of disease in the community. Sample size was small. Same radiologist did CT scan and MRI interpretation hence, interobserver agreement could not be tested. MRA using 3D TOF did not include cervical vessels and intracranial venous imaging for interpretation. Patients with multiple lesions were excluded from the study.

Cerebral Infarction is associated with significant morbidity and mortality. Correct choice of therapeutic options rests upon timely and accurate diagnosis. In this regard, CT scan is a quick and comparatively easily available modality. But it fails to diagnose some cases of acute infarction. Magnetic resonance imaging particularly DWI has a 100% sensitivity in diagnosing acute infarction. Computed tomography scan can be used as an initial tool of investigation in patients with suspected ischaemic stroke. However, MRI should be considered in patients who do not have any signs in CT scan but have persistent symptoms. Magnetic resonance spectroscopy can be used as identifying tool for time since occurrence in stroke however further study is required. A 3D TOF can identify the arterial territory but sensitivity is less. Therefore, an initial CT scan followed by a FLAIR and DWI may be postulated as best diagnostic protocol for ischaemic stroke patients. This study concludes that the Sensitivity and Specificity of CT scan is lower than MRI.