Attenuation Of SPECT/PET And Application In Differentiation Of TCM

BackgroundAttenuation correction is a hot topic in nuclear medicine imaging.The gamma photons from deep organ travel a longer distance to the detector than that from the superficial organ near the skin do.So do the photons from the deep position and the superficial position in the same organ.The photons from the body it would be attenuated in their intensity by the soft tissue before they reach the detector.Some of them lost more intensity then others when coming from the deeper body.Attenuation of the photons would distort the image,affect the image quality,and may lead to misdiagnosis.In the past, the most method of attenuation correction used a equation which uses a fixed attenuation constant for all parts of the body,such as Chang's method.But this method has some disadvantages,it assumes that the density of the tissue is uniform.However,actually,only the brain tissue is nearly uniform,and other organs are not the same,the application of this assumption to other parts of the body,such as chest,is restricted.In our research the X ray and gamma ray was used as transmission resource for accurate assessment of attenuation in each part of the body.The transmission data was used to correct the emission data from the body.Iteration algorithm was used for the reconstruction of attenuation corrected tomography images.Object:1.Evaluate the efficacy of attenuation correction in duel head hybride SPECT/coincidence PET systems(SPECT/PET)and SPECT using both the Jasczak and the myocardial phantoms.2.Evaluate the efficacy of attenuation corrected tumor and myocardial image in patients using duel head hybride SPECT/coincidence PET systems (SPECT/PET)and SPECT.3.To correlate the results of clinical imaging and the symptom patterns that are based on the theory of traditional Chinese medicine,and try to identify the relationship between them.Method:1.For PET phantom study,the Jasczak phantom was filled with the aqueous solution of F-18 and was scanned with two hybride SPECT/coincidence PET systems respectively(Vertex plus,ADAC company and Hawkeye,GE company).The PET images were acquired and reconstructed.2.The PET patient study was performed in 192 patients,110 males:110, aged 26-85(average:59.52)years old and 82 females aged 30-81(average:58.02) years old.All of them were the outpatients or inpatients of our hospital from June,2001 to March,2005.After fasting:for more than 6 hours,the patient's blood sugar was under 7.0mmol/l,and the F-18-FDG was injected intravenously with 1.85Mbq/kg.The patients were instructed to lay in the bed for 1 hour after the injection,and to empty the urinary bladder,before the PET images were acquired.The emission images were acquired with 2 or 3 bed positions according to scanning range,and 50%overlap between the scans.The image matrix of 128×128×16 was used for acquisition.The collimator is MCGP one. The emission scan was acquired by steps with 32 azimuths per scan,and the 1st azimuth was acquired for 40 seconds.After the acquisition of the emission images,the transmission correction data was acquired with 2 seconds per azimuth,for a total of 96 azimuths.The emission image was acquired with duel energy windows,centered at 511keV(the primary photopeak of 18F)with energy window width of 30%and at 310keV(the Compton window of 18F)with energy window width of 30%;The transmission image was acquired with single energy window,centered at 662keV(the primary photopeak of 137Cs)with energy window width of 20%.First emission image was acquired for the calculation of subsequent decay correction.So the acquisition time per step was successively increased according to the decay time.The reconstruction parameters is as below:coincidence detection iterative,iterations:2,filter:Weiener,NF%: 0.75,smoothing:axial smoothing.The non-attenuation correction images and attenuation correction images were reconstructed respectively,and then knitted(2 or 3 scan).The transaction,coronal and sagittal images were generated.Analysis and interpretation of the image:the image interpretation was given by two nuclear medicine physicians who have more than 10 year experience in nuclear medicine,and the interpretation was given according the counts of the focus that was obviously higher than opposite or the surrounding normal tissue.We examined the cancer patients with the same method of acquisition,reconstruction and analysis.The patients with cancers were divided into 2 groups to access these two coincidence PET camera systems in detecting of large metastatic lesion and small metastatic lesion(early metastasis).3.For SPECT phantom study,the cardiac phantom was filled with Tc-99m or TL-201 separately for the background(28.03KBq/ml for Tc-99m,5.6KBq/ml for TL-201),the "myocardial"(670KBq/ml for Tc-99m,100KBq/ml for TL-201), the ventricle(390KBq/ml for Tc-99m,33.48KBq/ml for TL-201).The Tl-201 was filled one week after the Tc-99m experiment,The cardiac phantom was put on the scanning table,with the axis of the "heart" tilted 15°to the table,and the data of the phantom was acquired.The acquisition parameters were as below: the phantom was placed on the table,two detector formed as 90°,the acquiring oval track was played as 180°,with low energy high resolution collimator, with 99Tcm-MIBI,64 azimuths was acquired,25sconds per azimuth,the matrix size is 64×64×16,Zoom=1.46,with 201Tl,32 azimuths was acquired,40 seconds per azimuth,the matrix size is 64×64×16,Zoom=1.46.The parameter of reconstruction:(1)Filter Projection reconstruction primary image(with noncorrection system),filter:Butterworth,99Tcm-MIBI:Order=10,Cutoff=0.50; 201Tl:Order=5.0,Cutoff=0.40;(2)iterative reconstruction(with correction system),iterations:12,filter:Butterworth,99Tcm-MIBI:Order=5.0,Cutoff = 0.66:201Tl:Order=5.0,Cutoff=0.35.Interpretation:(1)Reading by 3 physicians of nuclear medicine,analysis the correction and noncorrection image respectively,and then the diagnosis was given with the same view;(2) The ratio of inferior wall/anterior and lateral wall/septum were calculated according to the same size of rectangle ROI's accounts on the wall.We acquired the image with the myocardial phantom filling with Tc-99m and Tl-201,and read them naked eyes and counts rates to analysis.4.42 patients with coronary heart disease,there were 20 male ones and 22 female ones,aged 36～82 years old,average 56.4 years old.The diagnosis was made based on International Society of Heart Disease and Standardization of the World Health Organization named the Joint Task Team Report:Ischemic heart disease and the naming of the diagnostic criteria.The symptom differentiation was made by the physicians of traditional Chinese medicine, Patients were divided into 2 groups:deficiency symptom mainly and positive symptom mainly to analysis their result of image of myocardial.Results1.The corrected image of Vertex Plus was improved obviously;the disparity of counts between surrounding and deep center less,and the counts in deep center was compensated.The cold lesion which the diameter was less than 12mm of uncorrected image could be identified.But it,diameter 9mm,would be recognized clearly,less than 7mm would not be distinguished.Noncorrect image could only identify hot lesion which the diameter was 9 mm,14 mm, 18 mm,22mm and 38mm,while in the corrected image,not only it was much better, but also the hot lesion of 6mm was distinguished.In Hawkeye,the same situation, the corrected image of was improved obviously;the disparity of counts between surrounding and deep center less,and the counts in deep center was compensated. There were only 3 round cold lesions could be recognized,the diameter:14 mm,18mm,20mm;all of them which diameter were less than 12mm could be distinguished.One in the center was almost as background,and could not be identified.The radioactive accounts of Surrounding and center were quite different.The corrected image 5 cold lesions could be find,9mm,12 mm,14 mm,18mm and 20mm,but 7mm could not be find.The noncorrected image,only 14 mm,18 mm,22 mm and 38mm hot lesions could be find,and by the surrounding, there was a arc shape hot lesion.But we could distinguish 9mm,14 mm,18 mm, 22 mm和38mm hot lessions on the corrected image,and the image was much better the noncorreted one.2.192 patients were examined by DHPET,among them,166 were positive, and 33 were negative.369 focuses were found before correction,and 455 focuses were found after correction.12 focuses less than 2cm were found before correction,but there were 99 focuses found after correction,and the difference was obviously.The focuses large than 2cm were all be found in 2 methods,and no significance between them.The inpatients were divided in 2 groups:deficiency syndrome mainly and others,and the X2 test showed:no significantly difference between 2 groups,large than 2cm or less than 2cm. The focus less than 2cm mean early metastasis.3.The phantom image show:the effect of correction image was better on 99Tcm-MIBI than 201Tl,especially when the defect is in the lateral wall near the base of the heart.The imaging with 99Tcm-MIBI or 201Tl did not show the defect in nocorrected image,but on the attenuation corrected image,the same lesion was shown clearly.4.The group of positive symptom mainly:11 patients,among them there were 5 positive,the rate was 45.45%;The group of deficiency symptom mainly: 31 patients,among them there were 19 positive,the rate was 61.29%.The difference between 2 groups was not obviously.Conclusions1.After attenuation,the image was much better than before,but the noise was multiplied too.So the T/B was not a good manner to express the uptake of the tumor.2.Attenuation correction was a good methodto detect smaller focus of cancer or metastasis,and less misdiagnosis,and benefit to early diagnosis and early treatment.3.Attenuation correction was very important in the myocardial SPECT,it could reduce misdiagnosis,especially in the inferior and posterior wall.4.We tried to do something combine the SPECT/PET with Traditional Chinese Medicine,and that was Only a start,we should to try more in the future,and hope to have a nice outcome someday.