<div class="__aliyun_email_body_block"><div  style="clear:both;"><div  class=" __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;"><span  style="margin:.0px;padding:.0px;border:.0px;outline:.0px;font-family:Arial,sans-serif;font-size:15.0px;text-align:justify;">Dear CASToR Users and Developers,</span><br ></div><div  class=" __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;"><div  class=" __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor" id="sign_card2" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-size:16.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:left;text-indent:.0px;text-transform:none;widows:2;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;"><div  class=" __aliyun_node_has_color __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;">We have using CASToR to recon our PET data for half a year, and it shows impressive ability to provide the image that we urgently needed. But there are two problems that confused me：</div></div></div></div><div  style="clear:both;"><div  class=" __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;"><div  class=" __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor" id="sign_card2" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-size:16.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:left;text-indent:.0px;text-transform:none;widows:2;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;"><div  class=" __aliyun_node_has_color __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;">1）How does CASToR generate its System Matrix when running OSEM? I used to know that before running MLEM iterative reconstruction, one should precompute the system matrix for the current specific PET scanner system, which will cost a lot, and must re-generate it when changing different PET scanner geometry. But CASToR needs no precomputation and can recon any kind of PET geometry immediately, how does it happen?</div></div></div></div><div  style="clear:both;"><div  class=" __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;"><div  class=" __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor" id="sign_card2" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-size:16.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:left;text-indent:.0px;text-transform:none;widows:2;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;"><div  class=" __aliyun_node_has_color __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;">2）When does Point Spread Function calculation be used in MLEM iteration? I compared MLEM reconstruction with and without PSF calculation, and find out that the MLEM with PSF provides far better image results than another. <span  style="font-family:Tahoma,Arial,STHeiti,SimSun;">In the attachment, I showed the reconstructed image of Derenzo by CASToR</span><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;"> with PSF</span><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;">, its image quality is good!  I just what to in which step does PSF work in CASToR MLEM iteration? Does anyone know which <span  style="color:#000000;font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline;">article</span> I should read？</span></div></div></div></div><div  style="clear:both;"><div  class=" __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;"><div  class=" __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor" id="sign_card2" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-size:16.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:left;text-indent:.0px;text-transform:none;widows:2;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;"><div  class=" __aliyun_node_has_color __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;"><br ></span></div></div></div></div><div  style="clear:both;"><div  class=" __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;"><div  class=" __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor" id="sign_card2" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-size:16.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:left;text-indent:.0px;text-transform:none;widows:2;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;"><div  class=" __aliyun_node_has_color __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;clear:both;"><span  class=" __aliyun_node_has_color __aliyun_node_has_color __aliyun_node_has_color" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;"><span  class=" __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor __aliyun_node_has_color __aliyun_node_has_bgcolor" style="margin:.0px;padding:.0px;border:.0px;outline:.0px;color:#000000;font-family:Tahoma,Arial;font-size:14.0px;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;text-align:start;text-indent:.0px;text-transform:none;widows:2;background-color:#ffffff;text-decoration-thickness:initial;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline;">Thank you a lot </span></span>for your help, any answer will be helpful.</div></div></div></div><div  style="clear:both;">Christopher Zhao</div><div  style="clear:both;"><br ></div><div  style="clear:both;"><br ></div><div  style="clear:both;"></div></div>