The Value Of 18F-FDG PET/CT Dual-phase Imaging In The Diagnosis Of Fever Of Unknown Origin

Objective:To explore the value of 18F-FDG PET/CT dual-phase imaging and some laboratory tests in diagnosing the etiology of PATIENTS with FUO,understand the imaging characteristics and metabolic manifestations of PATIENTS with FUO,and provide basis and help for clinical diagnosis.Methods:Ninety-one patients with fever of unknown origin in our hospital from January2019 to December 2021 were retrospectively collected,including 49 males and 42 females.The patients were 22-89 years old,with a mean of 63±17.4 years old.All patients underwent dual-phase 18F-FDG-PET/CT imaging,namely conventional imaging for 1h and delayed imaging for 2h.According to the etiology of FUO,FUO was divided into 4 groups: Group A(infectious disease),group B(malignant tumor),Group C(non-infectious disease)and Group D(others).The etiology of Group D was unknown and should not be discussed.PET/CT images of patients were collected and the 1h SUVmax value and 2h SUVmax value of patients’ lesions were obtained by AW4.6 workstation,and then Δ SUVmax value =(2h SUVmax value-1h SUVmax value)/1h SUVmax value was calculated.Some basic information and laboratory test results of patients were obtained through the hospital record system,including age,sex,underlying diseases,WBC count,RBC count,CRP and ESR,etc.The experimental results of group A,GROUP B and group C were compared with the values of1 h SUVmax,2h SUVmax and δ SUVmax by inter-group T test(conforming to normal distribution)or Mann Whitney U test(not conforming to normal distribution),and P<0.05 was statistically significant.Results:A total of 91 patients met the inclusion criteria,including 43 patients with infectious diseases(47.2%),22 patients with malignant tumors(24.1%),and 17 patients with non-infectious diseases(18.7%).The fever of the remaining 9 patients subsided without definite cause,and no patient died without confirmed cause.Infectious diseases included pulmonary infection in 17 cases(39.5%),intravascular infection in 18 cases(41.8%),skin and soft tissue infection in 3 cases(6.9%),and cytomegalovirus disease(CMV)in 5 cases(11.6%).Intravascular infections mainly included valvular endocarditis and infection caused by implanted cardiac devices.Malignant tumors were divided into 15 cases(68.2%)of hematological tumors and 7cases(31.8%)of solid tumors,including lymphoma 12 cases(54.5%)and leukemia 3cases(13.7%),nephrectoma 4 cases(18.2%)of solid tumors and colorectal cancer 3cases(13.6%).Non-infectious diseases included: macrovasculitis in 11 cases(64.7%),adult still disease in 5 cases(29.4%),systemic lupus erythematosus in 1 case(5.9%).The remaining 9 patients with fever of unknown cause had not been diagnosed until the fever disappeared.The mean age of patients was 63±17.4 years,47 patients were over 65 years old,accounting for 49.5%.Male 57 cases(62.6%);Laboratory results included in this study included white blood cells,red blood cells,platelets,ESR,and CRP.The number of WBC was statistically significant among different groups(P=0.04).Patients diagnosed with benign disease tended to have elevated white blood cells,while those diagnosed with malignant cancer had significantly lower white blood cell counts than those with benign disease.There was no statistical significance in RBC count and ESR between the 4 groups(P= 0.62,P=0.83).CRP had statistical significance for the comparison between group A,group B and group C,where P=0.003 between group A and group B,P=0.008 between group A and group C,and P=0.01 between group B and group C.Therefore,CRP had statistical significance for the differential diagnosis of infectious,malignant or non-infectious FUO.SUVmax of conventional 1h imaging was 5.7±2.6;SUVmax of 2h delay imaging was 6.0±2.5;δSUVmax was 7.9±1.4%.The SUVmax value of 1h imaging for malignant tumors was8.3±3.4,the SUVmax value of 2h delayed imaging was 11.4±3.4,δ SUVmax value was11.8±2.1%.The lesions showed focal high uptake with high or medium uptake in surrounding lymph nodes.The 1h SUVmax value of non-infectious lesions was 3.7±1.8,2h SUVmax value was 3.9±2.1,δ SUVmax value was 5.7±1.3%.The images of lesions were mostly scattered throughout the body,showing moderate and low uptake.By contrast,SUVmax values of malignant tumors were significantly higher than those of infectious lesions(P=0.003<0.01)and non-infectious lesions(P=0.005<0.01)in conventional 1H imaging,so the difference was statistically significant.There was no significant difference in SUVmax between infectious and non-infectious lesions(P=0.193>0.01).In 2h delay imaging,the δ SUVmax values of malignant tumor lesions were still significantly higher than those of infectious lesions(P=0.001<0.01)and noninfectious lesions(P=0.001<0.01),indicating statistically significant differences.Theδ SUVmax value of infectious lesions was significantly higher than that of noninfectious lesions,and the difference was statistically significant(P=0.007<0.01).The specific etiology of group D is unknown,so the results of group D are not discussed in this study.Conclusion:PET/CT dual-phase imaging has certain significance in the diagnosis of fever of unknown cause,and the combination of serum CRP level is helpful for the differential diagnosis of FUO.