Michael Kean1,2, Lee Coleman2,3, Simone Mandelstam3, Sonal Josan4, Benjamin Schmitt4, and Dingxin Wang5,6
1Children MRI Centre, Royal Childrens Hospital, Parkville, Australia, 2Murdoch Childrens Research Institute, Parkville, Australia, 3Royal Childrens Hospital, Parkville, Australia, 4Siemens Healthcare, Bayswater, Australia, 5Centre for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States, 6Siemens Medical Solutions, Malvern, PA, United States
Synopsis
The objective of our prospective study was to examine the clinical utility of Simultaneous Multi-Slice(SMS) Accelerated TSE at 3T imaging paediatric patients who present with seizures.A randomly selected cohort of patients were enrolled in the protocol covering a broad spectrum of clinical entities.
A direct comparison was undertaken with anatomically matched conventional TSE and SMS TSE acquisitions with matched in-plane and through plane resolution, echo train lengths and echo spacing.
Analysis of the data confirmed that although there were minimal variations in the quantitative measures recorded both sequences provided images of consistent image quality and diagnostic confidence with a significant scan time reduction attributed to the SMS TSE acquisition.
Purpose
The objective of this study was to
determine if the implementation of simultaneous multi-slice (SMS) TSE in 3T clinical epilepsy protocols would impact
the diagnostic accuracy of whole brain T2 weighted TSE acquisitions.
Historically the inefficient data
acquisition strategies of T2 weighted sequences have proved to be a limiting
factor in the acquisition of high resolution T2 weighted scans. Advances in MR
hardware, sequences [1,2] and reconstruction techniques [3,4] have enabled high-resolution
T2 weighted acquisitions to further define anatomical
anomalies associated with epilepsy. Scan time reduction with under sampling techniques
such as GRAPPA and SENSE comes at the expense of a reduction in signal
to noise (SNR). The early development of
simultaneous multi-slice acquisitions [4,5,6] demonstrated the potential for
more slice efficient acquisitions per TR to reduce scan times without the SNR
penalties attributed to under-sampling techniques. The development of phase and
slice based acceleration techniques such as CAIPIRINHA [4] has enabled the
development of simultaneous multi-slice TSE sequence[8] that can be
applied to clinical T2 weighted imaging. Our work investigates the implementation
of a SMS TSE sequence with CAIPIRINHA
[9] into standard clinical protocols.
Methods
A randomly selected cohort of 20 patients
referred for clinical epilepsy scans underwent our routine whole brain hi-resolution
T2 weighted TSE epilepsy protocol using a standard TSE sequence and
anatomically matched SMS TSE sequence. All patients were scanned on Verio
or Trio, A Tim System 3T MR scanners (Siemens Healthcare, Erlangen, Germany) using the product 32channel receive only head
coil.
Integral to our experimental design was the
requirement to obtain all SMS TSE acquisitions with the system operating in
normal transmit SAR mode. The pulse sequence incorporates RF
management utilizing VERSE pulses.
Imaging parameters for the acquisitions :
TSE – TR 4280ms TE 89ms, FOV 220 75%, 56
slices 3 concatenations 1 acq, resolution 2.5 x 0.5 x 0.5mm non interpolated,
ETL 17 Esp 12.7ms (4.18mins)
SMS TSE : TR 5960ms TE 89ms, FOV 220 87.5%,
56 slices , resolution 2.5 x 0.5 x 0.5mm non interpolated, ETL 16 Esp 12.8, slice acceleration factor 2, FOV shift 2. (2.41mins).
Quantitative post acquisition analysis of
all data was performed using standard syngo.MR Multi-Modality Workplace (Siemens
Healthcare). Qualitative interpretation of all images was undertaken by 2
experienced pediatric neuro-radiologists using PACS workstations. All image reviewers were blinded to the acquisition strategy. Image analysis consisted of (a) image quality based on quantitative analysis (b)
qualitative radiologist based diagnostic
interpretation. Image quality analysis comprised SNR comparisons of CSF, GM and
WM, CNR measurements of GM-WM , image sharpness and physiological based artifacts.
Radiologist scoring of the data reflected diagnostic confidence, overall image
appearance and artifacts originating from physiological sources
Results
Figure 1 is a representative coronal T2 slice orientated perpendicular to the hippocampus, this slice was chosen to demonstrate the capabilities of the sequence because of the complex anatomy and potential for artifacts originating from physiological sources.
Figure 2 Coronal T2 weighted acquisition comparing TSE(a) and SMS TSE(b) in a patient with multiple Periventricular Nodular Heterotopia (PVNH)
Figure 3 Coronal T2 weighted acquisition comparing TSE(a) and SMS TESE(b) in a patient with a probable Dysembryoplastic Neuroepithelial Tumour (DNET) involving anterior temporal lobe structures
Table 1 Shows the signal to noise (SNR) and contrast to noise (CNR) analysis of 6 randomly selected studies. The data demonstrates the flexibility of sequence parameters to almost replicate the quantitative values from the standard TSE acquisitions.
Table 2 Summarises the image interpretation scoring of 18 patients data with both sequences demonstrating a very high degree of diagnostic confidence.
The reduction of CSF signal was attributed to magnetization transfer effects associated with the application of the multiband RF pulse but did not affect the diagnostic confidence of radiologists.The overall impression was that the TSE accelerated acquisition appeared slightly sharper but this was probably due to the reconstruction algorithm used by the sequence developer and a slightly higher noise level.
Conclusion
Analysis of our data has confirmed that
simultaneous multi-slice TSE can be successfully implemented into standard
clinical epilepsy protocols with significant scan time reductions. Importantly,
the overall image quality was comparable and provided radiologists with images
of appropriate image contrast and resolution to enable reporting of cases with
a high diagnostic confidence rating comparable to standard industry accepted standards.
Acknowledgements
Acknowledgement : Siemens Medical Solutions for
access to works in progress (WIP) package and ongoing scientific support . Staff and patients
of Childrens MRI Centre Royal Childrens Hospital Melbourne, AustraliaReferences
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