The　magnetic　field　strength　of　magnetic　particle　imaging　(MPI)　detection　devices　(excite　and　receive　coils)　has　a　direct　impact　on　the　detection　signal　of　magnetic　nano　particle　(MNPs)　magnetization　response.　The　non-uniformity　of　the　magnetic　field　makes　reconstructing　MNP　concentration　challenging　by　detection　signals　in　the　reconstruction　algorithms　such　as　x-space　and　projection　reconstruction　(PR).　Although　the　System　matrix　imaging　algorithm　or　additional　correction　algorithm　can　correct　the　error　caused　by　the　non-uniform　magnetic　field　of　detection　devices,　it　is　complex　and　costly.　Therefore,　it　is　necessary　to　design　a　detection　device　with　a　highly　uniform　magnetic　field.This　study　investigated　the　importance　of　magnetic　field　uniformity　of　MPI　detection　devices　in　x-space　and　PR　imaging　algorithms　after　revealing　the　relationship　between　the　detection　signal,　the　peak　intensity　of　the　excitation　magnetic　field,　and　the　sensitivity　of　the　receiving　magnetic　field.　A　modified　open　detection　device　with　Square　Helmholtz　coils　was　proposed.　The　Square　Helmholtz　coil　provides　a　uniform　magnetic　field　while　maintaining　the　detection　device＇s　openness.　The　detection　Performance　of　the　proposed　and　two　traditional　open　detection　devices　were　evaluated　in　two　scenarios:　field　free　point　(FFP)　and　field　free　line　(FFL)　scanning　movement.It　is　noted　that　the　ideal　detection　signals　should　be　consistent　within　the　field　of　view　(FOV)　due　to　the　uniform　distribution　of　MNPs.　In　addition,　the　results　of　second-harmonic　and　third-harmonic　detection　were　compared.Simulation　results　show　that:　(1)　In　the　case　of　FFP　scanning　movement,　the　maximum　detection　errors　of　the　proposed　improved　open　detection　device　are　0.865%　and　1.977%　on　the　center　and　edge　planes,　respectively,　which　are　closer　to　the　ideal　detection　effect　than　the　two　traditional　ones.　(2)　The　FFL　scanning　movement　shows　similar　results　to　the　FFP　scanning　movement,　and　the　detection　accuracy　of　the　proposed　device　is　more　excellent　than　the　two　traditional　devices　under　the　same　condition,　with　maximum　detection　errors　of　0.51%　and　1.51%　on　the　center　and　edge　planes.　(3)　The　maximum　detection　errors　of　FFP　and　FFL　scanning　movement　cases　can　be　reduced　from　1.977%　and　1.51%　of　the　third　harmonic　detection　to　1.247%　and　0.98%　of　the　second　harmonic　detection.The　following　conclusions　can　be　drawn.　(1)　In　FFP　or　FFL　scanning　movement,　the　detection　Performance　of　the　proposed　device　is　closer　to　the　ideal　detection　than　the　two　traditional　open　detection　devices,　which　is　suitable　for　the　X-space　and　PR　imaging　algorithms.　(2)　When　the　proposed　device　is　considered　for　the　image　reconstruction,　the　second　harmonic　detection　helps　to　reduce　the　detection　errors　and　improve　detection　results　compared　to　the　third　harmonic　detection.　©　2025　China　Machine　Press.　All　rights　reserved.