SWI has been increasingly shown to be a useful non-contrast enhanced imaging sequence in the evaluation of acute stroke. One of the most important recent applications of SWI is imaging stroke. It is well known that reliable detection of the ischemic penumbra has a significant impact on treatment and management, especially for acute stroke patients. SWI could be a powerful tool for better detection of the ischemic penumbra .
In acute stroke with arterial vessel occlusion, SWI-like sequences may depict clot-related susceptibility changes known as the susceptibility. The SWI plays an important role is detection the area at risk depending on evaluation the asymmetrical prominent vessel sign .
In our study, SWI was done for 25 patients and we found that 16 patients had APVS in their images representing 64% compared to 9 patients who had negative images. These results are in agree with (Chen et al. 2015) who did his study on 22 patients and found that APVS was detected in 15 patient representing about 68% and 7 patients had negative APVS. They stated that the APVS on SWI is a signature of salvageable ischemic tissue that will become infarcted if blood perfusion cannot be established in time .
Luo et al. (2015) reported that the APVS occurred in 11 (61%) of 18 patients with cerebral infarction on SWI. Their findings showed that a finding of APVS on SWI was significantly associated with the occurrence of damaged vessels or the presence of thrombus in the affected vessels .
SWI such as APVS was associated with damaged vessels or the presence of thrombi in the affected vessels. SWI could thus provide information on the status of blood vessels in patients with acute cerebral infarction in addition to that provided by other currently used imaging methods .
(Chen et al. 2015) study results showed out of 15 patients with positive APVS 9 of them had arterial occlusion proving that there is great correlation between the APVS and arterial occlusion .
In our study, we also found that caudate nucleus was the least affected area; we only found 1 patients had APVS in the caudate nucleus representing about 4%; on the other hand, 15 case showed APVS in M3, 4, 5; thus, they were the most affected areas compared to the deep structures.
These results are in agree with (Chen et al. 2015) who did his study on 22 patients and found that about 9 patients had APVS in the same areas like our study M3, 4, 5 but with lower percentage, and they agree with our study as regarding the least affected area which was caudate nucleus, which can be explained by the admixed venous flow in the thalamostriate vein, which drains not only these structures, but also the thalamus .
Jiang et al. 2021 stated that the occurrence rate of APVS was 67.9% in patients with anterior circulation infarct. Most previous studies on APVS have focused on anterior circulation stroke .
All patients with APVS changes had CTP changes so 16 out of 19 patients with CTP had APVS representing 84%, and only 3 has negative APVS. On the other hand; no one with negative CTP had APVS; there was good correlation between the CTP and APVS with significant p value.
These results are in agreement with (Wang et al. 2017) and (Wu et al. 2017) who found that there is significance correlation between the CTP and APVS with significant p value [22, 23].
In our study, we used ASPECT to read the CTP, SWI, and DWI to be able to detect the affected areas more easily without bias and we found the mean ASPECT score for SWI 4 ± 1.4 and mean aspect for DWI 7.6 ± 1.2; in addition, mean aspect for CTP was 4.6 ± 1.3. From these results, we found there is significance difference between the SWI and DWI with significant P value. On the other hand, there is no significance difference between the SWI and CTP ASPECT scores.
These results are consistent with research done by Wang et al. (2017) and Wu et al. (2017) who found that there is no significance difference between the SWI and CTP ASPECT scores, but on the other hand there is significance difference between the SWI and DWI ASPECT scores [22, 23].
In our study, only 16 patients with positive APVS showing SWI/ DWI mismatch representing 64% and 9 patients (36%) showed negative APVS with no definite mismatch. On the other hand, 19 patients showed prolonged MTT in CTP representing 76% and 6 patients have negative results representing 24%. After statistical analysis, there is no significant difference between the SWI/DWI mismatch and CTP/DWI mismatch.
Wang RY 2021  concluded that The MTT is very sensitive to measuring the ischemia state of brain tissue, and it has been used to define the ischemia scope. Several research types have also proved that the increase in oxygen extraction fraction (OEF) is related to the extension of MTT. Since the SWI is sensitive to the change of OEF of deoxy-haemoglobin, SWI can provide a similar metabolic capability to MTT. Furthermore, an SWI-DWI mismatch and a DWI-PWI (MTT) mismatch have similar abilities .
Wang et al. 2017 study included 47 patients and they found that only 16 patients had APVS and 19 patients had positive perfusion finding with SWI/DWI mismatch that is correlated with CTP/DWI mismatch with no significant difference between the SWI and CTP in detection of area at risk which is in agreement with our research 
A study done by Liu et al. 2016 showed that SWI/DWI is positively correlated with PWI/DWI and PWI-DWI mismatch volumes; their results indicated that SWI-DWI mismatch has the ability to detect penumbra .
Wang RY 2021 who did their research on 52 patients found that 32 patients have DWI-SWI mismatches; they stated that by contrasting the DWI-SWI mismatch with the DWI-PWI mismatch in evaluating the ischemic penumbra and found that a DWI-SWI mismatch has a similar ability as a DWI-PWI to detect the ischemic penumbra, which indicates that SWI can be used to forecast the ischemic penumbra of patients with acute ischemic cerebral stroke; they concluded also that increased and thickened venous shadows in the SWI sequence of the hypoperfusion area compared with the contralateral .
In addition, Luo et al. 2015 found that DWI-SWI mismatch was positively correlated with the DWI-MTT mismatches. These findings suggested that similar to the DWI-MTT mismatch, the DWI-SWI mismatch could reflect the size of ischemic penumbra in patients with cerebral infarction .
However, Verma et al. found that although SWI is helpful in detecting tissue at risk, it cannot replace PWI. The reason might be that MTT detects more ill-perfused areas than SWI, especially in good collateralized subjects [26, 27].
SWI is a technique that is contrast independent, consuming less time, and can be considered as an alternative to CT Perfusion valuable in detecting penumbra and help to rapidly directing patients indicated for thrombolytic therapy.