| 1. |
- Dahlbom, Magnus, et al.
(författare)
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Effects of high photon fluence rate from therapeutic radionuclides on preclinical and clinical PET systems
- 2016
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Ingår i: 2014 IEEE Nuclear Science Symposium and Medical Imaging Conference, NSS/MIC 2014. - 9781479960972
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Konferensbidrag (refereegranskat)abstract
- Tumor response in radionuclide therapy can be monitored with PET/CT and/or PET/MR. A high background photon fluence from a therapy radionuclide may influence both image quality and quantification, when imaging is performed intra-therapeutically, i.e. with high activity of the therapeutic radionuclide present. Here, count losses and image distortion have been investigated for preclinical and clinical PET systems with different detector designs. The effect on the spatial resolution was studied with a point source of 22Na in a background of 99mTc, where 99mTc emulated the photon emission from a therapeutic radionuclide. An in-house made mouse phantom with silicon tubes filled with 99mTc with a centrally placed 22Na point source was used. For the clinical systems, a 70 cm long NEMA PET Scatter Phantom was used, with a 22Na point source placed at the center whereas the off-center silicon tube was filled with 99mTc. In addition, image quality was also evaluated in the presence of different levels of 99mTc with a 18F-filled NEMA image quality phantom on the preclinical systems and a 18F-filled Jaszczak phantom on the clinical system. Preclinical PET systems with different detector geometries showed that the addition of 99mTc affected the count rate capability considerably, especially those with a low number of read-out channels. The coincidence rate for was significantly reduced when high activities of 99mTc were present. The clinical PET system also showed an effect of reduced coincidence rate with increased photon fluence rate. At high 99mTc activities, the spatial resolution was degraded for both the preclinical and the clinical systems. The quantitative capability of PET systems used intra-therapeutically is significantly affected by the additional high photon fluence rate. The dead-time correction implemented on some of the investigated PET systems, was able to accurately compensate for the coincidence count losses. The reduced spatial resolution at high photon fluence rate, however, remains a potentially limiting factor.
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| 2. |
- Madru, Renata, et al.
(författare)
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(68)Ga-labeled superparamagnetic iron oxide nanoparticles (SPIONs) for multi-modality PET/MR/Cherenkov luminescence imaging of sentinel lymph nodes.
- 2014
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Ingår i: American journal of nuclear medicine and molecular imaging. - 2160-8407. ; 4:1, s. 60-69
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to develop (68)Ga-SPIONs for use as a single contrast agent for dynamic, quantitative and high resolution PET/MR imaging of Sentinel Lymph Node (SLN). In addition (68)Ga enables Cherenkov light emission which can be used for optical guidance during resection of SLN. SPIONs were labeled with (68)Ga in ammonium acetate buffer, pH 5.5. The labeling yield and stability in human serum were determined using instant thin layer chromatography. An amount of 0.07-0.1 mL (~5-10 MBq, 0.13 mg Fe) of (68)Ga-SPIONs was subcutaneously injected in the hind paw of rats. The animals were imaged at 0-3 h and 25 h post injection with PET/CT, 9.4 T MR and CCDbased Cherenkov optical systems. A biodistribution study was performed by dissecting and measuring the radioactivity in lymph nodes, kidneys, spleen, liver and the injection site. The labeling yield was 97.3 ± 0.05% after 15 min and the (68)Ga-SPIONs were stable in human serum. PET, MR and Cherenkov luminescence imaging clearly visualized the SLN. Biodistribution confirmed a high uptake of the (68)Ga-SPIONs within the SLN. We conclude that generator produced (68)Ga can be labeled to SPIONs. Subcutaneously injected (68)Ga-SPIONs can enhance the identification of the SLNs by combining sensitive PET and high resolution MR imaging. Clinically, hybrid PET/MR cameras are already in use and (68)Ga-SPIONs have a great potential as a single-dose, tri-modality agent for diagnostic imaging and potential Cherenkov luminescent guided resection of SLN.
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| 3. |
- Mellhammar, Emma, et al.
(författare)
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An attenuation method for reducing count rate losses in preclinical PET during intratherapeutic imaging
- 2017
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Ingår i: 2016 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop, NSS/MIC/RTSD 2016. - 9781509016426 ; 2017-January
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Konferensbidrag (refereegranskat)abstract
- In pre-clinical imaging, tumor response to radionuclide therapy can be monitored with PET imaging. Radionuclides used for therapy such as 177Lu emit a significant amount of low energy photons. These photons may have an energy high enough to penetrate the imaged object and are the prone to be detected. Although these phtons are likely to be rejected electronically, they add dead-time to the system since they need to be processed by the electronics. This is a problem in high-sensitivity pre-clinical PET system with a low number of readout channels, such as the Genisys G8 investigated in this work. The low energy gammas may also affect image quality due to increased probability of pulse pile-up. The use of high-attenuating shields designed to absorb most of the low energy photons emitted from the therapeutic radionuclide were investigated. Cylindrical led shields were constructed with thicknesses between 1 and 3 mm. A 3mm thick cylindrical shield was also constructed out of Rose metal (50% Bi, 28% Pb, and 22% Sn). The diameter of the shield was wide enough to accommodate a NEMA IQ phantom and a mouse. The attenuation of the shields for annihilation radiation was measured with a 22Na point source placed at the center of the FOV. Measurements of the coincidence rate were performed with the lead shields in place. At a of thicknesses of 1 and 3mm, the coincidence rate was reduced by a factor or 0.70 and 0.40, respectively. To study the effect of the presence of a background of low energy gammas on the coincidence count rate and the efficacy of the lead shields, 177Lu was added to a 1 cm diameter hollow sphere. In the presence of 100 MBq of 177Lu, the coincidence count rate was reduced by a factor 0.20 due to the detector dead-time. Although the count rate was reduced by a factor of 0.40 with the 3mm shield around the source, the dead-time effects due to the 177Lu background were less than 7%. 18F imaging of a NEMA phantom and a tumor bearing mouse showed dramatic image distortions in the presence of the 177Lu background. When imaging of with the 3mm shield in place, the image distortions were eliminated and were comparable in to the images acquired without the background activity.
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| 4. |
- Mellhammar, Emma Matilda, et al.
(författare)
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Count rate characteristics and image distortion in preclinical PET systems during intratherapeutic radiopharmaceutical therapy imaging
- 2016
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Ingår i: Journal of Nuclear Medicine. - : Society of Nuclear Medicine. - 0161-5505 .- 2159-662X. ; 57:12, s. 1964-1970
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Tidskriftsartikel (refereegranskat)abstract
- Positron emission tomography (PET) may provide important information on the therapeutic response of radiopharmaceutical therapy (RPT) during therapy. The radiation emission from the RPT radionuclide may disturb the coincidence detection and impair the image resolution. In this study we tested the feasibility to perform intratherapeutic PET on three preclinical PET systems.METHODS: Using (22)Na point sources and phantoms filled with (18)F, and a phantom filled with either (99m)Tc or (177)Lu, the coincidence count rate and the spatial resolution when both a PET and a therapeutic radionuclide were present in the PET camera, were evaluated. (99m)Tc was used as a substitute for a generic therapeutic radioisotope, since it has a suitable half-life and is easy obtainable.RESULTS: High activities of (99m)Tc deteriorated the coincidence count rate from the (18)F-filled phantom with a (22)Na point source on all three systems evaluated. One of the systems could to a high degree correct the count rate with its dead time correction. The spatial resolution was degraded at high activities of (99m)Tc for all systems. On one of the systems (177)Lu increased the coincidence count rate and slightly affected the spatial resolution. The results for high activities of (177)Lu were similar to those for (99m)Tc.CONCLUSION: Intratherapeutic imaging might be a feasible method to study RPT treatment response. However, some sensitive preclinical PET systems, unable to handle high count rates, suffer count losses and may also introduce image artifacts.
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| 5. |
- Vilhelmsson Timmermand, Oskar, et al.
(författare)
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Intratherapeutic Biokinetic Measurements, Dosimetry Parameters Estimate, and Monitoring Treatment Efficacy using Cerenkov Luminescence Imaging in Preclinical Radionuclide Therapy.
- 2015
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Ingår i: Journal of Nuclear Medicine. - : Society of Nuclear Medicine. - 0161-5505 .- 2159-662X. ; 56:3, s. 444-449
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, there has been an increasing amount of interest in non-invasive Cerenkov Luminescence Imaging (CLI) of in vivo radionuclide distribution in small animals, a method proven as a high-throughput modality for confirmation of tracer uptake. 11B6 is an IgG1 monoclonal antibody that is specific for free human kallikrein-related peptidase 2 (hK2) an antigen abundant in malignant prostatic tissue. Free hK2 was targeted in prostate cancer xenografts using (177)Lu-labeled 11B6 in either murine or humanized forms for radionuclide therapy (RNT). In this setting, CLI was investigated as a tool for providing parameters of dosimetric importance during RNT. First, longitudinal imaging of biokinetics using CLI and single-photon emission computed tomography (SPECT) was compared. Second, the CLI signal was correlated to quantitative ex vivo tumor activity measurements. Finally, CLI was used to monitor the radionuclide treatment and it was found that the integrated CLI radiance correlated well with subject-specific tumor volume reduction.
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