He-Kwon Song, PhD Associate Professor & Co-investigator in the CMROI, Department of Radiology, University of Pennsylvania School of Medicine, Philadelphia, PA

CMROI Slide 2 Dynamic KWIC  A novel technique has been proposed for dynamic MRI: Dynamic KWIC  Permits image reconstruction at both high spatial and high temporal resolutions  Technique is based on an angle-interleaved projection reconstruction (PR) data acquisition and temporally selective data filtering  Effective temporal resolution is equal to a highly undersampled PR technique, but image quality similar to a fully sampled data set

CMROI Slide 3 Rim enhancement Spiculated/smooth Focal/lobular High spatial resolution High temporal resolution Need for High Spatial and Temporal Resolutions

CMROI Slide 4 k x k y A C B A B A B D C D C D  k * Song, et al. MRM 44: (2000). KWIC* = K-space Weighted Image Contrast Conventional projection reconstruction MRI acquires data that lie along radial lines in k-space (a). The inset figure shows the region surrounding the center of k-space. Within the k-space "pixel" (dashed box), there is a high degree of oversampling. (b) In KWIC, the central region of k-space is occupied only by select views of interest (e.g., a single echo time in radial FSE, or a narrow temporal window in dynamic imaging). The adjacent annular region(s) of k-space is occupied by adjacent echoes or adjacent time frame. KWIC Data Acquisition and Reconstruction

CMROI Slide 5 512x384, 460µm Dynamic KWIC * Song, et al. MRM 52: (2004). In conventional DCE-MRI, long scan times are required to achieve high spatial resolution. Top: Four high resolution images, each requiring 2:00 acquisition time. Bottom: Dynamic KWIC images, where each high resolution data set was acquired in 8 underdsampled passes. The effective temporal resolution for each high-resolution image is 15 sec. Dynamic KWIC Image Acquisition & Reconstruction

CMROI Slide 6 15 sec/image; 512x48; 470µm 15 sec/image; 128x48; 1.9mm Dynamic KWIC 15 sec/image; 470µm Low SNR Low spatial resolution High SNR and high spatial resolution DCE-MRI with and without KWIC processing

CMROI Slide 7 Peak enhancement Time to maximum slope Wash-out rate Pre-contrast Post-contrast Parametric Maps

CMROI Slide 8 Conclusions  With angle-interleaved PR acquisition and temporally selective data filtering, both high temporal and high spatial resolutions can be achieved simultaneously.  The dynamic KWIC technique may be useful in various applications, including dynamic contrast- enhancement studies, hyperpolarized gas imaging, cardiac motion, and kinematic studies involving object motion.

CMROI Slide 9 PCA PCA can be used to analyze the dynamic time series of the undersampled radial data series. Components that primarily contribute to image streaking and noise are rejected, while those that contain information of the tumor are maintained. Undersampled dynamic series PCA processed series Low SNR Streaks Higher SNR Reduced streaks Principal Component Analysis of Undersampled Radial Data

CMROI Slide 10 Figure 1 Results from PCA processing of undersampled radial data set (a) Full dataset image: 512 points x 384 views (2 min acquisition). (b) Magnified and cropped image of (a). (c) Image from a single pass: 512 points x 48 views (15 sec). (d) PCA processed: 512 points x 48 views (15 sec). (e) Parametric map: RED = Signal wash-out, BLUE = Plateau. a b c e d Principal Component Analysis of Under-sampled Radial Data