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The Intricacies of Manufacturers and Filters in Nuclear Medicine Imaging

This article delves into the complexities of filter definitions in nuclear medicine imaging, focusing on Butterworth filters and variations in manufacturer recommendations. The discussion covers the impact of changing filter parameters on image quality and noise levels, with comparisons between Philips and GE filters. The text warns readers to scrutinize filter definitions, question manufacturer guidelines, and be cautious about unit conversions to avoid confusion. The importance of accuracy and double-checking filter settings is emphasized for professionals in nuclear medicine imaging.

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The Intricacies of Manufacturers and Filters in Nuclear Medicine Imaging

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  1. Manufacturers and Filters – Is it all still a bit fuzzy? Bill Thomson, James Cullis, Joe O’Brien Physics & Nuclear Medicine City Hospital. Birmingham

  2. Background

  3. MPI Images Philips Odyssey Butterworth filter: Order = 6.0 Cut-off = 0.24 cycles / pixel 6 mm pixel , = 0.4 cycles / cm G* X*l*r*s Manufacturer recommendations Butterworth filter: Power = 5 Critical Freq. = 0.5 cycles/cm G* X*l*r*s Butterworth filter: Power = 6 Critical Freq. = 0.4 cycles/cm

  4. What’s Going on ? Variation in filter definition ? Companies often make subtle changes to things

  5. Butterworth Filter Filter shape set by order and cutoff Fix cut-off = 0.3 pixel-1 Alter the ORDER

  6. Butterworth Filter Fix order = 6 Alter the CUT-OFF

  7. Effect of Varying Cut-off 0.12 pixel-1 0.18 pixel-1 0.24 pixel-1 0.3 pixel-1 0.36 pixel-1

  8. How Does All This Help? • More higher frequency terms, more noise • Need the ‘lower-mid’ frequencies for structure

  9. Butterworth Filter Comparison Philips: Order 6 , Cut-off 0.4 cm-1 GE: Power 6 , Critical Freq. 0.4cm-1

  10. Filter Definitions PhilipsGE 1/2 ( ) Order Number n Power = 2n Cut-off at 0.5 critical freq. = 0.707

  11. Butterworth Filter Comparison Philips: Order 6 , Cut-off 0.4 cm-1 GE: Power 12 , Critical Freq. 0.4cm-1

  12. Butterworth Filter Comparison Philips: Order 6 , Cut-off 0.4 cm-1 GE: Power 12 , Critical Freq. 0.37cm-1

  13. PhilipsGE Short Axis Comparison Order 6.0 Cut-off 0.4 cycles/cm Power 12.0Critical Freq.0.37 cycles/cm

  14. Manufacturers Comparison Cut-off Definition Cut-off units Order number Philips n 0.5 per pixel Philips n 0.5 per 2 pixels GE power = 2n 0.707 per cm-1 Hermes n 0.5 per cm-1 Siemens n 0.5 per Nyquist* * ( Nyquist is 0.5 pixel -1 )

  15. Published recommendations QGS order = 5 , cut-off 0.41 cycles per cm-1 EANM guidelines Says ‘ correct cut-off is at 0.707 ‘ Cut-off = 0.3 – 0.4 Nyquist , pixel size = 6mm Different cut-off values depending on MBq. Definition of Nyquist and pixel size relationship is wrong. BNMS Order 5 or 10 , cut-off 0.5 cycles per cm-1 (? Pixel size ) but cut-off = 0.75 for Hanning ? SNM Useless

  16. Published recommendations (2) SNM Useless G Germano, Cedars-Sinai* Equates cut-off and critical frequency States is at 0.5, but graphs show both 0.5 and 0.707 * “Technical Aspects of Myocardial Imaging”JNM, 42: no 10 1499-1507 , 2001

  17. Summary • Take great care! • Check filter definition and units • Don’t always trust the manufacturer to be right • Convert units and double-check! • Beware! Confusion in other areas eg DaTSCAN

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