Background New Cross Hospital is a 700 bed DGH located in central England Regional Heart & Lung centre opened in 2005 Covering the Black Country (Population >1,000,000)
Nuclear Medicine Department Single Camera Department 2800 scans per year Including ~ 800 MPS scans Dec 08 Mk 1 Brightview was installed 2009 MPS service established Aug 2010 upgraded to Brightview XCT
New NICE (National Institute for Clinical Excellence) Guidelines released emphasising a move away form Exercise ECG to Imaging in early assessment of CAD Increased referrals, increasing waiting list Need to increase patient throughput Aim was to decrease imaging time without affecting image quality
Standard MPS protocol Two day protocol 6 min Adenosine Stressing 400-800MBq 99m Tc Myoview (weight dependent) Fatty meal / Drink Images acquired 30 min post injection Rest scans performed 48hrs later
Imaging parameters LEHR collimators 64 x 64 Matrix 64 projections 30s per view Attenuation correction using XCT ECG gating 16 Bins 20% window (Max 40%)
Reconstruction parameters Astonish recon algorithm Images Iterations Subsets Hanning Filter Cutoff Scatter correction Static 4 8 1.50 No Attenuation correted 4 8 1.75 Yes Gated 4 8 0.75 No
Study breakdown Image Jaszczak Phantom using all available parameters at 10,15,20,25 & 30s per view Image Cardiac Phantom with best 4 parameters between 10,15,20,25 & 30s per view Acquire half time images co-currently with full time images for clinical / gated assessment
1 GBq 99m Tc injected into Jaszczak phantom 360 SPECT acquisition Parameters (all permutations used) Acquisition time per projection Matrix Number of projections 10 64 x 64 32 15 128 x 128 64 20 256 x 256 128 25 30
64 x 64 matrix produced the most uniform image when compared to other matrices 64 x 64 matrix yielded best SNR No difference between contrast 256 x 256 matrix and 128 projections resulted in unacceptably long reconstruction times and were eliminated
A cardiac phantom, with added defect, was filled with 13.5 ± 2.6 MBq of 99m Tc
The phantom was imaged, within the shell of a Jaszczak phantom, filled with water, using SPECT (clinical setup)
Short axis slice of cardiac phantom following reconstruction with Astonish Line profile drawn across the diameter and used to measure the FWHM of the phantom wall and to calculate the contrast within the image
FWHM (pixels) 40 35 30 25 20 15 10 5 0 0 200 400 600 800 1000 Total scan duration (s) 64m32p 64m64p 128m32p 128m64p A one-way ANOVA was performed on the data collected from different scan durations using the 64 x 64 matrix and 64 projection angles. It was found that there was no effect of scan duration on the measured FWHM of the wall of the cardiac phantom using these parameters (P=0.95)
Contrast 2.5 2 1.5 1 0.5 0 0 200 400 600 800 1000 Acquisition time (s) 64m32p 64m64p 128m32p 128m64p A one-way ANOVA was performed on the data collected from different scan durations using the 64 x 64 matrix and 64 projection angles. It was found that there was no effect of scan duration on the contrast within the short axis slice of the cardiac phantom image using these parameters (P=0.80).
Using the Autoquant software we created and compared polar plots to our Original data looking for % difference over key segments Polar plot segmental assessment
Percentage difference over Segment 10
Percentage difference over key segments
Scan times of longer than 480 seconds in duration were deemed unnecessary Taking all data into consideration it was decided that clinical data would be acquired using a 64 x 64 matrix, 64 projections and 15 seconds per projections, concurrently with the current protocol
Short axis, HLA and VLA slices, showing a stressed myocardium using full time and half time imaging The defect in the lateral part of the inferior wall is clearly visible and is consistent between full and half time imaging
Half time stress and rest polar plots Full time stress and rest polar plots
Images of difference in uptake within the myocardium between full and half time imaging at rest and under stress The calculated extent of the defects within the myocardium when comparing FT and HT acquisitions of the 23 patients analysed was not significantly different Rest (FT : 3 ± 4 %; HT: 3 ± 4 %; p = 0.79, t-test). Stress (FT : 5 ± 6 %; HT: 6 ± 7 % ; p = 0.73, t-test) rest full time rest half time comparison stress full time stress half time comparison
Full time ejection fraction (%) 100 90 80 70 60 50 40 R² = 0.9626 p < 0.001 R² = 0.9455 p < 0.001 40 50 60 70 80 90 100 Half time ejection fraction (%) Rest Stress There was no difference between the calculated LVEF from 23 patients when comparing the FT (69 ± 13 %) and HT (69 ± 13 %) (p = 0.98; t-test) stress images and also the FT (70 ± 14 %) and HT (69 ± 13 %) (p = 0.98; t-test) rest images. Linear regression analysis showed a significant relationship between FT and HT calculated LVEF for both stress and rest studies (p < 0.001)
Following the analysis of 23 patients, there has been no difference in clinical outcome using full time or half time imaging Data suggests that half time acquisition can be used without compromising image quality or calculation of LVEF Half Time imaging is now in clinical use
Acknowledgements This Study was performed by: Dr Tim Watts, BSc, B.Med.Sc, Phd Trainee Clinical Scientist, New Cross Hospital
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