Radiolabeling of herceptin with [99m]Tc as a her2 tracer

Trastuzumab is a monoclonal antibody that is used in treatment of breast cancer. We labeled this monoclonal antibody with Technetium-99m and performed in vitro and in vivo quality control tests as a first step in the production of a new radiopharmaceutical. Trastuzumab was labeled with Technetium-99m using Succinimidyl Hydrazinonicotinamide [HYNIC] as a chelator. Radiochemical Purity and stability in buffer and serum were determined. Immunoreactivity and toxicity of the complex were tested on SKBR3, MCF7 and A431 breast cancer cell lines. Bioedistribution study was performed in normal mice at 4 and 24 h post injection. The radiochemical purity of the complex was 95+/-1.4%. The stabilities in phosphate buffer and in human blood serum at 24 h post preparation were 85 +/- 3.5% and 74 +/- 1.2%, respectively. The immunoreactivity of the complex was 86 +/- 1.4%. The binding of labeled antibody to the surface of SKBR3, MCF7 and A431 cells were increased by increasing the human epithelial growth factor receptor 2 [Her2] concentration on the cells surface. These findings showed that the new radiopharmaceutical can be a promising candidate as Her2 antigen scanning for human breast cancer

Preparation and biodistribution study of [99m]Tc-EC-Annexin-SPIO as a tracer of radiation induced apoptosis in mice model

Apoptosis is a major consequence of ionizing radiation in proliferative tissues and quantification of the apoptotic cells could be helpful for noninvasive assessment and estimation of the radiation absorbed dose. Annexin V conjugated with super paramagnetic iron oxide nanoparticles [ANX-SPIO] is a biological probe for detection of apoptotic cells using magnetic resonance imaging. This study aimed at assessing the biodistribution alterations of the labeled ANXSPIO within the mice body shortly after exposure to different doses of ionizing radiation. [99m]Tc-EC-ANX-SPIO was prepared and its in vitro stability was tested. The binding affinity of radiocomplex to apoptotic cells was validated in vitro. Mice irradiated whole body with 2, 4 and 6 Gy [[60]Co gamma rays] and six hours later, radiocomplex was administrated intravenously and the biodistribution study was conducted 0.5, 1 and 2 hours later. The radiochemical purity of radiocomplex was 94% +/- 3.4% and it showed a good stability in PBS and serum. The radiocomplex maintained its efficacy for in vitro binding to apoptotic cells. radiocomplex accumulated in the bone marrow of all irradiated mice [p <0.05]. However, statistical analysis did not show significant correlation between the %ID/g of the femoral bones and the received radiation doses. Quantification of ANX-SPIO in bone marrow can be used as an indicator for radiation exposure but development and optimization of the assay are necessary for discrimination between different radiation doses

model based, anatomy dependent method for ultra-fast creation of primary SPECT projections

Monte Carlo [MC] is the most common method for simulating virtual SPECT projections. It is useful for optimizing procedures, evaluating correction algorithms and more recently image reconstruction as a forward projector in iterative algorithms; however, the main drawback of MC is its long run time. We introduced a model based method considering the effect of body attenuation and imaging system response for fast creation of noise free SPECT projections. Collimator detector response [CDR] was modeled by layer by layer blurring of activity phantom using suitable Gaussian functions. Using the attenuation phantom, in each angle, attenuation factor [AF] was calculated for each voxel. This calculated AF is the weight for the emission voxel and states the detection probability of photons that are emitted from that voxel. Finally weighted ray sum of the blurred phantom was driven to create a projection. For the next projection, our phantom was rotated and the procedure was repeated until all projections were acquired. Root Mean Square error [RMS] between all 60 modelled projection and real MC simulated projections was decreased from 0.58 +/- 0.15 using simple Radon to 0.19 +/- 0.03 using our suggested model. This value was 0.56 +/- 0.16 using blurred Radon without attenuation modelling, and 0.21 +/- 0.03 using attenuated Radon without CDR modelling. Our suggested model that considers the effect of both attenuation and CDR simultaneously results in more accurate analytical projections compared with conventional Radon model. Creation of 60 primary SPECT projections in less than one minute may make this method as a proper alternative for MC simulation. This model can be used as a forward projector during iterative image reconstruction for correction of CDR and attenuation that is necessary for quantitative SPECT

[Compensation of cross-contamination in simultaneous 201Tl/99mTc myocardial perfusion SPECT imaging]

It is a common protocol to use 201Tl for the rest and 99mTc for the stress cardiac SPECT imaging. Theoretically, both types of imaging may be performed simultaneously using different energy windows for each radionuclide. However a potential limitation is the cross-contamination of scattered photons from 99mTc and collimator X-rays into the 201Tl energy window. We used a middle energy window method to correct this cross-contamination. Using NCAT, a typical software torso phantom was generated. An extremely thin line source of 99mTc activity was placed inside the cardiac region of the phantom and no activity in the other parts. The SimSET Monte Carlo simulator was used to image the phantom in different energy windows. To find the relationship between projections in different energy windows, deconvolution theory was used. We investigated the ability of the suggested functions in three steps: Monte Carlo simulation, phantom experiment and clinical study. In the last step, SPECT images of eleven patients who had angiographic data were acquired indifferent energy windows. All of these images were compared by determining the contrast between a defect or left ventricle cavity and the myocardium. We found a new 2D kernel which had an exponential pattern with a much higher center. This function was used for modeling 99mTc down scatter distribution from the middle window image. X-ray distribution in the 201Tl window was also modeled as the 99mTc photopeak image convolved by a Gaussian function. Significant improvements in the contrast of the simultaneous dual 201Tl images were found in each step before and after reconstruction. In comparison with other similar methods, better results were acquired using our suggested functions. Our results showed contrast improvemtn in thallium images after correction, however, many other parameters should be evaluated for clinical approaches. There are many advantages in simultaneous dual isotope imaging. It halves imaging time and reduces patient waiting time and discomfort. Identical rest/stress registration of images also facilitates physicists' motion or attenuation corrections and physicians' image interpretation

[Assessment of the wavelet transform for noise reduction in simulated PET images]

An efficient method of tomographic imaging in unclear medicine is positron emission tomography [PET]. Compared ta SPECT, PET has the advantages of higher levels of sensitivity, spatial resolution and more accurate quantification. However, high noise levels in the image limit its diagnostic utility. Noise removal in nuclear medicine is traditionally based on Fourier decomposition of images. This method is based on frequency components, irrespective of the spatial location of the noise or signal. The wavelet transform presents a solution by providing information on the frequency content while retaining spatial information. This alleviates the shortcoming of the Fourier transform and thus, wavelet transform has been extensively used for noise reduction, edge detection and compression. In this research, we used the SimSET software to simulate PET images of the NCAT phantom. The images were acquired using 250 million counts in a 128 x 128 matrix. For the reference image, we acquired an image with high counts [6 billion]. Then, we reconstructed these images using our own software developed in MATLAB. After image reconstruction, a 250 million counts image [noisy image] and a reference image were normalized and then root-mean-square error [RMSE] was used to compare the images. Next, we wrote and applied de-noising programs. These programs were based on using 54 different wavelets and 4 methods. De-noised images were compared with the reference image using RMSE. Our results indicate that the Stationary Wavelet Transform and Global Thresholding are more efficient at noise reduction compared to the other methods that we investigated. The wavelet transform is a useful method for de-noising of simulated PET images. Noise reduction using this transform and loss of high-frequency information are simultaneous with each other. It seems that we should attend to the mutual agreement between noise reduction and the visual quality of the image

Respiratory Motion Detection and Correction in ECG-Gated SPECT: a New Approach

OBJECTIVE: Gated myocardial perfusion single-photon emission computed tomography (GSPECT) has been established as an accurate and reproducible diagnostic and prognostic technique for the assessment of myocardial perfusion and function. Respiratory motion is among the major factors that may affect the quality of myocardial perfusion imaging (MPI) and consequently the accuracy of the examination. In this study, we have proposed a new approach for the tracking of respiratory motion and the correction of unwanted respiratory motion by the use of respiratory-cardiac gated-SPECT (RC-GSPECT). In addition, we have evaluated the use of RC-GSPECT for quantitative and visual assessment of myocardial perfusion and function. MATERIALS AND METHODS: Twenty-six patients with known or suspected coronary artery disease (CAD)-underwent two-day stress and rest (99m)Tc-Tetrofosmin myocardial scintigraphy using both conventional GSPECT and RC-GSPECT methods. The respiratory signals were induced by use of a CT real-time position management (RPM) respiratory gating interface. A PIO-D144 card, which is transistor-transistor logic (TTL) compatible, was used as the input interface for simultaneous detection of both ECG and respiration signals. RESULTS: A total of 26 patients with known or suspected CAD were examined in this study. Stress and rest myocardial respiratory motion in the vertical direction was 8.8-16.6 mm (mean, 12.4 +/- 2.9 mm) and 7.8-11.8 mm (mean, 9.5 +/- 1.6 mm), respectively. The percentages of tracer intensity in the inferior, inferoseptal and septal walls as well as the inferior to lateral (I/L) uptake ratio was significantly higher with the use of RC-GSPECT as compared to the use of GSPECT (p < 0.01). In a left ventricular ejection fraction (LVEF) correlation analysis between the use of rest GSPECT and RC-GSPECT with echocardiography, better correlation was noted between RC-GSPECT and echocardiography as compared with the use of GSPECT (y = 0.9654x + 1.6514; r = 0.93, p < 0.001 versus y = 0.8046x + 5.1704; r = 0.89, p < 0.001). Nineteen (19/26) patients (73.1%) showed abnormal myocardial perfusion scans with reversible regional myocardial defects; of the 19 patients, 14 (14/26) patients underwent coronary angiography. CONCLUSION: Respiratory induced motion can be successfully corrected simultaneously with the use of ECG-gated SPECT in MPI studies using this proposed technique. Moreover, the use of ECG-gated SPECT improved image quality, especially in the inferior and septal regions that are mostly affected by diaphragmatic attenuation. However, the effect of respiratory correction depends mainly on the patient respiratory pattern and may be clinically relevant in certain cases.

[Energy window setting for optimum Tl-201 cardiac imaging]

Poor sensitivity and poor signal to noise ratio because of low injected thallium dose and presence of scattered photons are the main problems in using thallium in scintigraphic imaging of the heart. Scattered photons are the main cause of degrading the contrast and resolution in SPECT imaging that result in error in quantification. Thallium decay is very complicated and photons are emitted in a wide range of energies of 68-82 keV. It seems possible to achieve better primary to scattered radiation ratio and better image sensitivity simultaneously if the energy window setting is carefully selected. This investigation was performed in three steps: Monte Carlo simulation, phantom experiment and clinical study. In simulation step, the new 4D digital NCAT phantom was used to simulate the distribution of activity [201Tl] in patient torso organs. The same phantom was used to simulate the attenuation coefficient of different organs of the typical patient's body. Two small defects on different parts of left ventricle also were generated for further quantitative and qualitative analysis. The simulations were performed using the SimSET simulator to generate images of such patient. The emissions arising from Tl-201 decay were simulated in four steps using the energies and relative abundances. Energy spectra for primary and scatter photons were calculated. Changing the center and width of energy windows, optimum energy window characteristics were determined. In next step jaszczak phantom was prepared and used for SPECT imaging in different energy windows. In last step SPECT images of 7 patients who had angiographic data were acquired in different energy windows. All of these images were compared qualitatively by four nuclear medicine physicians independently. The optimum energy window was determined as a wider asymmetric window [77keV?30%] that its center is not placed on photo-peak of energy spectrum. This window increased the primary counts rate and PTSR considerably as compared with the conventional symmetric energy window [67keV%]. In a comparison which performed between clinical images acquired in suggested 77-30% window with conventional 67-20% window, a considerable increase was found in myocardial to defect contrast [1.541 +/- 0.368] and myocardial to cavity contrast [1.171 +/- 0.099]. A negligible increase was also found in total counts of images using this window. We found that conventional symmetric energy window [67keV +/- 10%] couldn't be a suitable choice for thallium heart imaging; furthermore three energy windows, 73keV-30%, 75keV-30% and 77keV-30%, were determined as optimum window options. For further analysis the images from such windows were compared in each three steps of this investigation. In all steps conventional symmetric energy window [67keV-20%] was introduced as the worst case and the asymmetric 77keV-30% was determined as the most suitable

Reducing the respiratory motion artifacts in pet cardiology: a simulation study

There are several technical features that make PET an ideal device for the noninvasive evaluation of cardiac physiology. Organ motion due to respiration is a major challenge in diagnostic imaging, especially in cardiac PET imaging. These motions reduce image quality by spreading the radiotracer activity over an increased volume, distorting apparent lesion size and shape and reducing both signal and signal-to-noise ratio levels 4D average male torso [2 cm diaphragmatic motion] produced by NCAT phantom was used for simulations. Emission sinograms generated by Eidolon PET simulator were reconstructed using iterative algorithm using STIR. The respiratory motion correction [RMC] applied to data sets using an automatic algorithm. Cross section views, activity profiles, contrast-to-noise ratios and left ventricle myocardium widths of corrected and non-corrected images were compared to investigate the effect of applied correction. Comparison of respiratory motion corrected and non corrected images showed that the algorithm properly restores the left ventricle myocardium width, activity profile and improves contrast-to-noise ratios in all cases. Comparing the contrast recovery coefficient []shows that the applied correction effected phases of number 7,8 and 9 of cardiac cycle more than the other 13 phases and the maximum value being 1.43 +/- 0.07 for phase number 8. The maximum value of ratio of the left ventricle myocardium width for non-RMC and RMC images along the line profile passing the apicobasal direction and along the line profile passing from the middle of the lateral wall of the left ventricle were 1.38 +/- 0.07 for phase number 9 and 1.12 +/- 0.03 for phases of number 8 and 9 respectively. Blurring and ghosting of each image depends on the speed of diaphragm during that respiratory phase. This simulation study demonstrates that respiratory motion correction has good overall effect on PET cardiac images and can reduces errors originating from diaphragmatic motion and deformation. Effect of such a correction varies from one cardiac phase to another and this depends on the blurring and ghosting of all respiratory phases used to form this cardiac phase. Using an automatic algorithm capable of correcting respiratory motion using full signal may be very useful to prevent lengthening of the overall scan time to obtain same motionless lesion signal levels

Qualitative evaluation of filter function in brain SPECT

Filtering can greatly affect the quality of clinical images. Determining the best filter and the proper degree of smoothing can help to ensure the most accurate diagnosis. Forty five patient's data aquired during brain phantom SPECT studies were reconstructed using filtered back-projection technique. The ramp, Shepp-Logan, Cosine, Hamming, Hanning, Butterworth, Metz and Wiener filters were examined to find the optimum condition for each filter. For each slice image, 6200 reconstruction options were considered. The corresponding planar image of each slice was used as the reference image. The quality of reconstructed images was determined using universal image quality index [UIQI]. Four nuclear medicine physicians evaluated the images to choose the best of the filters. Images with best resolution, contrast, smoothness and overall quality were selected by nuclear medicine physicians depending on filters used to generate the best image. A significant difference [p<0.05] between the filters regarding these parameters were observed. The results of this study revealed that maximum resolution and contrast could be obtained using both Metz and Wiener filters. However, the best quality images were generated by using Butterworth filter

Comparison of 6 PET scanners: a simulation study

Due to the large number of PET systems available in the market, it is not very easy to decide about the scanner of choice. Conducting a research in order to compare all different PET scanners is very time consuming and expensive and practically impossible. However, such comparison may be conducted using PET simulators. In this study, the performance of 6 different PET scanners in cardiology is evaluated using a dedicated PET simulator. In this study only the design of the system were evaluated. Activity and attenuation phantoms were produced using 4D-NCAT phantom. EC AT EXACT HR+, EC AT 953B, ECAT 966, EC AT ART, GE Advance and 16HI-REZ scanners were simulated using Eidolon PET simulator and the output sinograms were reconstructed using STIR software. The reconstructed images were processed using Interview software installed on the Mediso cardiac imaging system. Counts of pixels determined by ROI were used to drawn curves and then the correlations of these curves calculated using SPSS. True coincidences 2D was 4651791 +/- 5900 for ECAT 966, 4651965 +/- 5660 for ECAT ART, 4742731 +/- 5328 for ECAT EXACT HR+, 6018435 +/- 5167 for ECAT 953B, 6566769 +/- 4734 for GE Advance and 6846339 +/- 51850 for 16HI-REZ. Resulted correlations calculated for these scanners were 0.806, 0.795, 0.718, 0.858, 0.726 and 0.896 respectively. There was a considerable different in scatter fractions of different scanners. Curves drawn using count of pixels determined by ROI and correlations of these curves showed differences in performances of scanners in cardiology. The results showed that the 16HI-REZ scanner is the best scanner of the six scanners for simulating of cardiac PET images

new monoclonal antibody radiopharmaceutical for radioimmunoscintigraphy of breast cancer: direct labeling of antibody and its quality control

Radioimmunoscintigraphy [RIS] has found widespread clinical application in tumor diagnosis. The antibody [Ab] PR81 is a new murine anti-MUCl monoclonal antibody [MAb] against human breast carcinoma. In this study a very simple, rapid and efficient method for labeling of this MAb with [99m] Tc, particularly suitable for development of a [kit] is described. The reduction of Ab was performed with 2-mercaptoethanol [2-ME] at a molar ratio of 2000:1 [2-ME:MAb] and the reduced Ab was labeled with [99m] Tc via methylene diphosphonate [MDP] as a transchelator. The labeling efficiency which was determined by instant thin layer chromatography [ITLC] was 94.2% +/- 2.3. Radiocolloides measured by cellulose nitrate electrophoresis were 2.5% +/- 1.7. In vitro stability of the labeled product in human serum which was measured by gel filtration chromatography [FPLC] was 70% +/- 5.7 over 24 hr. The integrity of labeled MAb was checked by means of SDS-PAGE and no significant fragmentation was observed. The results of the cell-binding studies showed that both labeled and unlabeled PR81 were able to compete for binding to MCF 7 cells. Biodistribution studies were performed in normal BALB/c mice at 4 and 24 hrs post-injection and no important accumulation was observed in vital organs. These results show that the new radiopharmaceutical may be considered as a promising candidate for imaging of breast cancer

[ camera based calculation of 99mTc-MAG3 clearance using conjugate views method]

Background: measurement of absolute or differential renal function using radiotracers plays an important role in the clinical management of various renal diseases. Gamma camera quantitative methods in approximation of renal clearance may potentially be as accurate as plasma clearance methods. However some critical factors such as kidney depth and background counts are still troublesome in the use of this technique. In this study the conjugate-view method along with some background correction techniques have been used for the measurement of renal activity in 99mTc-MAG3 renography. Transmission data were used for attenuation correction and the source volume was considered for accurate background subtraction

Material and methods: the study was performed in 35 adult patients referred to our department for conventional renography and ERPF calculation. Depending on the patient's weight approximately 10-15 mCi 99mTc-MAG3 was injected in the form of a sharp bolus and 60 frames of 1 second followed by 174 frames of 10 seconds were acquired for each patient. Imaging was performed on a dual-head gamma camera [SOLUS; SunSpark10, ADAC Laboratories, Milpitas, CA]. Anterior and posterior views were acquired simultaneously. A LEHR collimator was used to correct scatter for the emission and transmission images. Buijs factor was applied on background counts before background correction [Rutland-Patlak equation]. Gamma camera clearance was calculated using renal uptake in 1-2, 1.5-2.5, 2-3 min. The same procedure was repeated for both renograms obtained from posterior projection and conjugate views. The plasma clearance was also directly calculated by three blood samples obtained at 40, 80, 120 min after injection

Results: 99mTc-MAG3 clearances using direct sampling method were used as reference values and compared to the results obtained from the renograms. The maximum correlation was found between conjugate view clearance at 2-3 min [R=0.99, R[2]=0.98, SE=15]. Conventional posterior view acquisition at the same time had showed less correlation [R=0.956, R[2]=0.914]. Both gamma camera methods after vascular activity subtraction revealed worse correlation [R=0.717 to 0.812]

Conclusion: conjugate view clearance can be used for calculation of renal clearance with a very good approximation. However in the presence of overlapping organs [Liver and spleen] may interfere with the results. Further work needed on to find the best method of background subtraction

[Appropriate energy window width for gamma camera]

Introduction: scatter radiation is one of the major sources of error in nuclear medicine data processing. Different methods of scatter correction have been introduced in order to improve the quality of data. However the best method is to avoid recording of scatter photons in acquisition. The only difference between scattered and non-scattered photons is the energy. Pulse height analyzer is the only option available to discriminate primary photons from scattered ones. Energy resolution of the gamma camera is gradually improving consequently the energy window width has to be decreased accordingly. In this study we tried to determine the most appropriate energy window width for present gamma camera systems

Methods and Materials: since it is not possible to retrieve the data spectrum from the most of the gamma camera systems, a simple method was developed to extract the data from the image of the energy spectrum. Using a scatter phantom different level of scatter and count rate were generated and corresponding energy spectrum data were analyzed. It was assumed that around the peak of the spectrum, the primary photons obey a Gaussian distribution

Results: the data were analyzed using three different methods. All methods prove that the optimum window width regarding the present gamma camera energy resolution is 15%. At this level, the scattered radiation is decreased to 5%. In comparison to the conventional widow width of 20%, the sensitivity does not change dramatically

Conclusion: at the present, for most gamma camera, the energy window width of 20% is recommended. However occasionally energy window width of 15% and 25% are also used. In this study the energy spectrum at different levels of scatter were analyzed and the most suitable energy window width was found to be 15% for the gamma camera having approximate energy resolution of 11%. At this window setting the scatter decreases to 5% of the total counts recorded. Visually the quality of the images dose not improves significantly. However accuracy of data quantification improve significantly