The goal in the development of RAPID was to automatically perform a time-critical assessment of potentially salvageable tissue in acute stroke patients. These data allow the physician to avoid potentially harmful reperfusion therapies in stroke patients with either a malignant profile or little salvageable tissue (1 (link)), without the need for a skilled operator to perform PWI and DWI analysis and quantification. Therefore, the system's performance and reliability in predicting mismatch was evaluated and compared to the analysis of the same data by an experienced stroke neurologist or neuroradiologist.
For testing and evaluation purposes, data from the DEFUSE multi-center (7 sites) trial (1) were analyzed. In this trial, single-shot GRE-EPI DSC-MRI perfusion MRI data were acquired at 1.5 T whole-body scanners. Depending on make and model, the scan parameters were as follows: TR = 1.4 - 2.0 s, TE = 40 - 60 ms, matrix 1282, field-of-view 24 cm, 12 - 16 slices (5 - 7 mm thick separated by gaps of 0 - 2 mm) to cover the supertentorial brain, and 40 - 80 time points. A single-dose bolus (0.1 mmol/kg) injection of a gadolinium-based paramagnetic tracer (gadopentetate dimeglumine or gadobenate dimeglumine) was administered typically 10 - 15 s after the start of the dynamic scan using a MR-compatible power injector followed by 20 - 25 ml of saline flush at the same flow rate.
In addition to the perfusion MRI data, diffusion-weighted MRI data were also obtained as part of the DEFUSE trial. Specifically, single-shot diffusion-weighted spin-echo EPI scans were acquired with the following scan parameters: TR = 4 - 6 s, TE = 60 - 80 ms, matrix 1282, field-of-view 24 cm, and 12 - 24 slices (5 mm thick separated by gaps of 0 - 2 mm). Diffusion-weighted images were acquired with encoding gradients played out separately along the three principal axes at a b-value of 1000 s/mm2 plus one scan where the diffusion-encoding gradients were turned off (b = 0 image), resulting in a total of 4 different diffusion weightings. Thereafter, the three directionally-dependent diffusion-weighted images were combined to generate an isotropic diffusion-weighted image (b = 1000 image).
The lesion volumes identified by RAPID were compared to those identified by a human reader in 63 out of 74 cases, where both DWI and PWI were available and of good diagnostic quality. PWI maps generated by RAPID (that included corrections for motion and different slice times in interleaved-slice EPI acquisitions) were used for both the manual and the automated Tmax lesion segmentation. Attention was paid by the human reader to check if the AIF used in PWI processing was selected appropriately. Additionally, both methods used identical segmentation criteria (ADC and Tmax thresholds). RAPID and the human reader used mismatch criteria that were based on the original DEFUSE study (1 (link)). A mismatch was considered positive if the difference between the PWI and DWI lesion volume was at least 10 ml and the PWI/DWI volume ratio was at least 1.2. The agreement between diffusion-perfusion-mismatch identified by the human reader and RAPID was analyzed by true positive and false positive rates. Here, the assessment of mismatch by the human reader was considered as ground truth (the ‘gold standard’). Finally, the inter-reader agreement between the human reader and the RAPID was assessed by Cohen's kappa value.
For testing and evaluation purposes, data from the DEFUSE multi-center (7 sites) trial (1) were analyzed. In this trial, single-shot GRE-EPI DSC-MRI perfusion MRI data were acquired at 1.5 T whole-body scanners. Depending on make and model, the scan parameters were as follows: TR = 1.4 - 2.0 s, TE = 40 - 60 ms, matrix 1282, field-of-view 24 cm, 12 - 16 slices (5 - 7 mm thick separated by gaps of 0 - 2 mm) to cover the supertentorial brain, and 40 - 80 time points. A single-dose bolus (0.1 mmol/kg) injection of a gadolinium-based paramagnetic tracer (gadopentetate dimeglumine or gadobenate dimeglumine) was administered typically 10 - 15 s after the start of the dynamic scan using a MR-compatible power injector followed by 20 - 25 ml of saline flush at the same flow rate.
In addition to the perfusion MRI data, diffusion-weighted MRI data were also obtained as part of the DEFUSE trial. Specifically, single-shot diffusion-weighted spin-echo EPI scans were acquired with the following scan parameters: TR = 4 - 6 s, TE = 60 - 80 ms, matrix 1282, field-of-view 24 cm, and 12 - 24 slices (5 mm thick separated by gaps of 0 - 2 mm). Diffusion-weighted images were acquired with encoding gradients played out separately along the three principal axes at a b-value of 1000 s/mm2 plus one scan where the diffusion-encoding gradients were turned off (b = 0 image), resulting in a total of 4 different diffusion weightings. Thereafter, the three directionally-dependent diffusion-weighted images were combined to generate an isotropic diffusion-weighted image (b = 1000 image).
The lesion volumes identified by RAPID were compared to those identified by a human reader in 63 out of 74 cases, where both DWI and PWI were available and of good diagnostic quality. PWI maps generated by RAPID (that included corrections for motion and different slice times in interleaved-slice EPI acquisitions) were used for both the manual and the automated Tmax lesion segmentation. Attention was paid by the human reader to check if the AIF used in PWI processing was selected appropriately. Additionally, both methods used identical segmentation criteria (ADC and Tmax thresholds). RAPID and the human reader used mismatch criteria that were based on the original DEFUSE study (1 (link)). A mismatch was considered positive if the difference between the PWI and DWI lesion volume was at least 10 ml and the PWI/DWI volume ratio was at least 1.2. The agreement between diffusion-perfusion-mismatch identified by the human reader and RAPID was analyzed by true positive and false positive rates. Here, the assessment of mismatch by the human reader was considered as ground truth (the ‘gold standard’). Finally, the inter-reader agreement between the human reader and the RAPID was assessed by Cohen's kappa value.
