<p>An excellent paper titled “Standardization of SPECT Filter Parameters” has been published in your esteemed Journal IJNM, 19(2): 30–35, 2004 by Dr A.K. Pandey et al. This paper will be very useful for all those new SPECT users to understand and use the filters judiciously for a better diagnosis. The authors have specifically chosen three filters to reconstruct the SPECT Phantom data and have not mentioned the reasons for selecting the same. The 3 Filters viz Hanning Filter, Butterworth Filter and Metz Filters have the following characteristics.</p><p>There are basically two types of filters used in SPECT. The smoothing and enhancement filters. The former uses low pass filter allowing the user to select the cutoff frequency. An example for this filter is Hanning filter. The Butterworth filter is also a smoothing filter allowing the user to select the cut off frequency. The Butterworth filter differs from the Hanning filter in that it maintains a value close to one at low frequencies and then rolls off steeply to zero value. The steepness of the rolloff is known as power factor. So this filter depends on cut off frequency and power factor.</p><p>The latter category of filters known as enhancement and restoration filters. These attempt to recover the resolution lost in the detection process by exceeding unity gain over a desired frequency band. Since noise dominates in the high frequency region, this filter at some point must also rolloff to zero. An example of this filter is Metz filter. This filter also depends on cut off frequency and power factor.</p><p>The Metz filter has superior characteristics and provided better images for Phantom studies. Nevertheless for clinical studies, Butterworth filter is preferred.</p></sec></body></article></article></body></html>

IJNM

Indian Journal of Nuclear Medicine

0972-3919

Society of Nuclear Medicine, India

ijnm-20-1-letter

EDITORIAL

Filters in SPECT imaging

Narayanan

R V

2005

20111

<p>An excellent paper titled “Standardization of SPECT Filter Parameters” has been published in your esteemed Journal IJNM, 19(2): 30–35, 2004 by Dr A.K. Pandey et al. This paper will be very useful for all those new SPECT users to understand and use the filters judiciously for a better diagnosis. The authors have specifically chosen three filters to reconstruct the SPECT Phantom data and have not mentioned the reasons for selecting the same. The 3 Filters viz Hanning Filter, Butterworth Filter and Metz Filters have the following characteristics.</p><p>There are basically two types of filters used in SPECT. The smoothing and enhancement filters. The former uses low pass filter allowing the user to select the cutoff frequency. An example for this filter is Hanning filter. The Butterworth filter is also a smoothing filter allowing the user to select the cut off frequency. The Butterworth filter differs from the Hanning filter in that it maintains a value close to one at low frequencies and then rolls off steeply to zero value. The steepness of the rolloff is known as power factor. So this filter depends on cut off frequency and power factor.</p><p>The latter category of filters known as enhancement and restoration filters. These attempt to recover the resolution lost in the detection process by exceeding unity gain over a desired frequency band. Since noise dominates in the high frequency region, this filter at some point must also rolloff to zero. An example of this filter is Metz filter. This filter also depends on cut off frequency and power factor.</p><p>The Metz filter has superior characteristics and provided better images for Phantom studies. Nevertheless for clinical studies, Butterworth filter is preferred.</p></sec></body></article></article></body></html>