¹⁸F-FDG PET/CT Imaging Findings Of Non-Hodgkin Lymphoma And Its Value In Clinical Staging

[Objective]1.To analyse the imaging findings and distribution of ¹⁸F-FDG PET / CT in Non-Hodgkin lymphoma to enhance the accuracy of diagnosis.2.To evaluate the value of PET/CT in the clinical staging of NHL.[Materials and Methods]1.Study objective1.1 Control groupSelecting 10 cases of the healthy physical examines in July 2007 to analyse the normal ¹⁸F-FDG PET/CT image,whose clinical examination,Electrocardiogram, X-Rays,B-ultrasound,serum tumor markers were all normal.1.2 NHL groupRetrospective analysis 88 cases with Non-Hodgkin lymphoma between Augest 2003 and March 2008,including 71 cases before treatment and 17 recurrence after treatment.64 were male and 24 were female.Ages ranged from 15 to 78 years,mean age was 50.All patients were taken whole body ¹⁸F-FDG PET/CT scan.The diagnosis of lymphoma was based on the pathologic results and the diagosis of NHL lesions was according to pathologic results of surgery or biopsy,and/or multi-modalities of imaging and clinical follow- up.2.Main equipments and imaging agentDiscovery LS PET/CT Scanner and PET tracerlab F-X_F-N from General Electric Company,¹⁸F-FDG was made by Automatic synthesis with a radiochemical purity over 95%.3.Imaging methods and conditionsSubject with more than 6 hours fasting,in a quite state,should be injected 203 MBq～511MBq(5.49 mCi～13.81 mCi) ¹⁸F-FDG at the hand vein by using the three-way pipe,later lying down in a darkroom for around an hour.The PET/CT scan was performed after the urination.The scan included CT plain scan and PET scan with a scan range from the middle of the femur to the calotte,6 to 8 bed positions. And the CT scan conditions were:140kV,160mA,pitch0.75,0.8second for tube lab rotation,5mm thickness,each emission scan time was 4minutes per bed position.4.Image reconstruction and image fusionThe PET images were reconstructed by OSEM method and images attenuation correction used CT data.CT images were reconstructed by the standard reconstrucion method.The matrix was 512 by 512,and the reconstructed slice thickness was 4.25mm.The PET and CT images were transmitted to Xeleris workstation to have the frame to frame image fusion display.5.Image analysis and Diagnostic CriteriaPET images and CT images were fused by frame to frame.And the images were analyzed by two experienced senior physicians in the filed of PET/CT diagnosis.The focus uptake close to that of the normal liver was defined as mild uptake,the focus dense higher than normal liver was defined as high uptake.The standardized uptake value(SUV) was calculated with the PET sanner soft-ware and average values in the ROIs were measured and record for each patients.The measurement method for the SUV of the NHL lesions:size and SUV were both measured if nodal lesions were less than three;If lymphatic nodes were diffusely involved,the largest,medium and smallest lesions were selected to measured for SUVs and sizes.If lesions were fused together like bolus,the most increased uptake lesion was measured for SUV.The whole organ was measured in the case of diffuse involvement.If the oran or tissue was involved with multiple lesions,every lesion was measured for size and SUV. Lesions which were found by CT but showed no uptake on PET,were considered as benign lesions after more than half a year follow-up.6.Staging criteriaAnn Arbor Staging Criteria7.Statistical MethodSPSS11.5 Statistical Processing Software was used in this study.The SUV datas were all recorded as average±Standard Deviation((?)±s).The SUVs of these three lymphoma groups(only with nodal involvement,only extrannodal involvement and both nodal and extranodal involvement) were tested by multi-sample nonparametric rank sum test(ruskal-Wallis H).The SUVs of nodal and extranodal involvement were compared and tested by two independent sample nonparametric rank sum test(Mann-Whitney U).The different sizes of lymph nodal lesions were compared and tested by multi-sample nonparametric rank sum test(Kruskal-Wallis H).The comparison of PET and integrated CT in coincidence rate of clinical staging were tested by x² test of two sample rate.All the statistics tests were seen statically significant when test level was less than 0.05.[Results]1.¹⁸FDG PET/CT imaging1.1 normal PET/CT studya good understanding of the normal physiology is important.From right to left the different planar images are a useful way to survey lesions on PET/CT.The brain is also a site of high FDG uptake due to marked glucose utilization,particularly in gray matter.FDG is cleared primarily through the renal system,so the renal calices,ureters and bladder are seen.there is mild generalized uptake in the liver,bone marrow and spleen.Normal variant uptake in the heart and bowel can be seen.Abnormal soft tissue mass was not seen on CT scan.1.2 ¹⁸F-FDG PET/CT imaging findings of NHLAmong 88 patients with NHL,77 with nodal involvement and 69 with extranodal involvement including 44(63.7%) with signal extranodal involvement and 25(36.2%) with multiple extranodal involvement.Most of the lesions were increased uptake of ¹⁸F-FDG.And 336 lesions were selected to measured,SUVs were 4.66±2.24. Among them there were 207 nodal lesions and 129 extranodal lesions and their SUVs were 4.36±2.19and 5.14±2.25 respectively,there was significant difference between them(Z=-3.187,P=0.001).207 nodal lesions were divided into three groups and their SUVs were measured.â… group:diameter(d)≤1.0cm,SUVs were 2.11±0.55;â…¡group: 1.0cm＜d＜2.0cm,SUVs were 4.263±1.31,â…¡group d＞2.0cm,SUVs were 6.32±1.78, there was not significant difference among them(x²=138.555,P＜0.001 ).According to involved location the subjects were divided into three groups including 19 cases with NHL only with nodal involvement,11 with only organ or tissue involvement and 58 with nodal and extranodal imvolvement.Their SUVs were 4.63±2.19,5.61±2.38 and 4.51±2.41 respectively.There was not significant difference among them (x²=3.296,P=0.192).1.2.1 The imaging finding and distribution of ¹⁸F-FDG PET/CT in NHL with nodal involvement.Among 77 patients with NHL of nodal involvement,lesions showed ¹⁸F-FDG high uptake in 71 patients and mild uptake in 2 patients.The other 4 were both high and mild uptake in a patient.After PET/CT scans were reviewed searching for specific patterns and distributions of nodal involvement of NHL,patients were classified as having the following three different patterns:whole-body multiple lesions with diffuse distribution,multi-lesions in multi-locations with scattering distribution and signal or multi-lessions in signal location with limited distribution. Diffuse distribution showed that whole-body lymph nodes were involved diffusedly along the lymphatic chain basically.Both side of the lymphatic chain were involved, some with symmetry and some without symmetry.This kind of pattern was observed in 22 of 77(28.6%) patients.Lymph nodes in multi-location were involved in whole body and the lesions were scattering and jumping distribution without traveling along the lymphatic chain basically.Abdomen,neck and axillary lymph nodes were usually involved and mediastinal lymph nodes were basically not involved.This kind of pattern was observed in 24 of 77(31.2%) patients.Limited distribution show that only a few of lymph nodes were involvment in a signal location.There were 31(40.3%) patients in this pattern and four of them showed bolus change.1.2.2 The imaging findings of ¹⁸F-FDG PET/CT in NHL with extranodal involvement.Among 69 patients with extranodal involvement NHL,lesions showed ¹⁸F-FDG high uptake in 67 patients and mild uptake in 2 patients on PET scans.44 were signal extranodal involvement and 25 were multi- extranodal involvement in a patient.After analysis the pattems and distributions of extranodal involvement of NHL on PET scans,patients were classified as having the following three different patterns:(1) diffuse infiltration;(2) multiple lesions;(3) signal lesion.In 44 signal extranodal involvement patients,diffuse infiltration was observed in 20 patients(45.5%),which showed that parenchymatous organ and tissue was diffusely high uptake or soft tissue mass.gastrointestinal tract lymphoma show diffuse uptake and diffusely thicking. gastral cavity was usually normal,but most of the enteric cavity showed aneurysmal dilatation.The pattern of multiple lesions was observed in10 patients(22.7%) in bone and bone marrow,brain and gastrointestinal tract.Brain involvement showed multi-increased uptake of FDG in the brain around the middle line structure and the uptake degree of lesions is higher than that of grey substance.Gastrointestinal tract involvement showed that multiple lesions were scattering in the gastric wall.Signal lesion was observed in 14 patients(31.8%) and there was no special features on PET/CT imaging.Among 25 patients with multiple extranodal involvements,there were different imaging findings in different organ or tissue in a patient,and diffuse infiltration was the very common sign.Two organ or tissue involved were observed in 9 patients,and at least one organ and tissue showed diffuse infiltration in 8 of 9 patients.1.2.3.The imaging findings of ¹⁸F-FDG PET/CT in NHL with both nodal and extranodal involvement.Among 88 patients,both nodal and extranodal involvement were observed in 58 patients(65.9%).And some imaging findings were special such as following. (1)Diffude lymph nodes involvements were usually in companion with spleen or bone marrow involvement.(2) When multiple extranodal involvement with nodal involvement,all lesions,among extranodal involvements and between extranodal involvement and nodal involvement,could not be explained by other maligant tumor.(3) when NHL with signal extranodal involvement in diffuse infiltration,its imaging was some special,especially in companion with distant lymph nodes involvedt.(4) When NHL with signal extranodal involvement in multiple lesions in companion with distant lymph nodes involvement,its imaging was also some special.2.The value of ¹⁸F-FDG PET/CT imaging in clinical staging of NHL71patients with NHL before treatment,19 were only nodal involvement and 52 were extranodal involvement with or without nodal involvement.PET/CT staging was matching with clinical staging in 68 patients,and the diagnosis accuracy was 95.8%. Among 19 patients with NHL of only nodal involvement,there was not significant difference between PET and integrated CT staging(x²=1.027,P=0.311).52 patients with NHL of extranodal involvement,there was significant difference between them (x²=12.56,P＜0.001).[Conclusions]1.¹⁸F-FDG PET/CT imaging is sensitive in detecting lymphatic lesions.Most lesions of NHL are high uptake of FDG.2.The distributions of lymphatic lesions are some special and benefit for diagnosis of NHL.3.There are three kind of imaging distribution of lymphatic nodes involved including whole-body multiple lesions with diffuse distribution,multi-lesions in multi-locations with scattering distribution and signal or multi-lessions in signal location with limited distribution.The two former are some special and benefit for the dagnosis of NHL.4.Extranodal involvement of NHL were classified as having the following three different patterns:diffuse infiltration,multiple lesions and signal lesion.Diffuse infiltration and multiple lesions in a signal organ or tissue are some special and can be considered as the diagnosis of NHL.5.Whole-body PET/CT imaging is sensitive in detecting nodal and extranodal lesions and has a high accuracy of diagnosis(95.8%) in clinical staging,which is a.very good technique in clinical staging.PET is more advantage in comparison with integrated CT in detecting extranodal lesions.