The major findings of the present study are that some acute infarctions were detectable only by TGSE-BLADE DWI whereas no lesions were detectable only by SS-EPI DWI, and that scores for geometric distortion, susceptibility artifacts, overall image quality, lesion conspicuity, and diagnostic confidence were higher for TGSE-BLADE DWI. Taken together, these imaging image characteristics indicate the potential utility of TGSE-BLADE DWI with SMS for diagnosis of acute infarction. In previous studies with TGSE-BLADE DWI, scan time was consistently 4 to 5 minutes4–9. The present study reports the first attempt to significantly reduce acquisition time to approximately 1 minute. The ability to scan images within this shortened timeframe, coupled with enhanced diagnostic capabilities for acute cerebral infarction compared to SS-EPI DWI, renders it highly valuable for routine clinical application.
Lesions that could not be identified after surgery as acute infarction on SS-EPI DWI were located near the cerebellar tentorium, cortex, hemorrhage, or pneumocephalus. A previous study has reported sensitivity of 81.1% and a false-negative rate of 5.6% for detecting infratentorial infarctions using 5 mm SS-EPI DWI, and lesions in false-negative cases were small24. Another study noted that most patients with false-negative lesions had infratentorial infarction or transient ischemic attack25. To mitigate false negatives, several reports have suggested that incorporating coronal sections or thin slice DWI can enhance diagnostic capabilities with SS-EPI DWI26,27. However, it might be possible to diagnose acute cerebral infarctions prone to false negatives using TGSE-BLADE DWI alone, and achieve diagnostic accuracy similar to that of additional imaging (such as coronal sections or thin slices) without acquiring additional scans.
Median scores for geometric distortion and susceptibility artifacts were 3.0 for SS-EPI DWI and 4.0 for TGSE-BLADE DWI. Distortion was also quantitatively less near the air-bone interfaces (e.g., frontal lobe, temporal tip, and pons) in TGSE-BLADE-DWI with SMS. These findings align with those of a prior study that used TGSE-BLADE DWI without acceleration technique9. Their scores for lesion conspicuity and diagnostic confidence in patients with acute or subacute infarction were lower in SS-EPI DWI than TGSE-BLADE DWI; however, median score was 4.0 for each sequence. In contrast, median score in post-surgery patients was 3.0 for SS-EPI DWI and 4.0 for TGSE-BLADE DWI. We consider that there is greater susceptibility postoperatively to artifacts due to air or hemorrhage, in which case TGSE-BLADE DWI is more beneficial.
SNR values were lower for TGSE-BLADE DWI than SS-EPI DWI in CSO. In SNR maps for temporal lobe, however, values were higher for TGSE-BLADE DWI than for SS-EPI DWI. TGSE-BLADE DWI showed less SNR degradation in areas prone to distortion, such as near air–bone interfaces, whereas SS-EPI DWI demonstrated superior SNR in other regions, primarily because only half of the signals are used in this sequence due to the non-CPMG (Carr-Purcell-Meiboom-Gill) problem. Another reason for the lower SNR values is that positioning the gradient echo with T2* decay effects at the center of k-space diminishes the image quality of TGSE-BLADE DWI5. Despite these disadvantages of 1-min TGSE-BLADE DWI, its ability to detect lesions located near susceptibility artifacts is a strong advantage.
There was no significant difference between the sequences in terms of ADC values in CSO or pons. In lesions, however, ADC values were significantly higher for TGSE-BLADE DWI than SS-EPI DWI, consistent with the findings of a previous study6. This discrepancy might have been due to the substantial differences in SNR and T1 values between normal tissue and lesions 28, but the cause remains unclear because no study has investigated cerebral infarction using TGSE-BLADE DWI. Furthermore, these differences might also have contributed to the lower CNR observed in TGSE-BLADE DWI. Whereas there was a strong correlation in ADC values for lesions between SS-EPI DWI and TGSE-BLADE DWI. Therefore, we consider that there should be few issues in clinical diagnosis.
There are several limitations in this study. Firstly, the sample size was small. A larger sample size might facilitate a more comprehensive investigation of lesions that could not be visualized by SS-EPI DWI. However, we prospectively enrolled over 100 patients, and believe that the number of cases was sufficient to demonstrate the utility of TGSE-BLADE DWI. Second, subacute infarct was diagnosed most commonly, and there were relatively few hyperacute infarcts. Due to the prospective nature of the study in which two types of DWI were acquired, it was challenging to perform these imaging examinations in patients with hyperacute stroke who require urgent treatment decisions. A previous study reported that some lesions were not depicted on SS-EPI DWI in the hyperacute stage29, indicating the need for further investigation in the future. Third, SMS imaging was not applied for SS-EPI DWI because we compared TGSE-BLADE DWI with SS-EPI DWI acquired with the protocol used at our institution. Although it is feasible to implement SMS for SS-EPI DWI, there is limited advantage because the shorter TR used has the effect of reducing SNR. Finally, in making the score judgments, the neuroradiologists noted that it was easy to distinguish the SS-EPI DWI and TGSE-BLADE DWI sequences based on the presence or absence of signal pile-up and geometric distortion.