Usefulness of 99mTc–pertechnetate SPECT-CT in thyroid tissue volumetry: phantom studies and a clinical case series

Background: An accurate measurement of the target volume is of primary importance in theragnostics of hyperthyroidism Objective: Our purpose was to evaluate the accuracy of a threshold–based isocontour extraction procedure for thyroid tissue volumetry from SPECT-CT. Methods: Cylindrical vials with a fixed volume of 99mTcO4 at different activities were inserted into a neck phantom in two different thickness settings. Images were acquired by orienting the phantom in different positions, i.e., 40 planar images and 40 SPECT-CT. The fixed values of the iso-contouring threshold for SPECT and SPECT-CT were calculated by means of linear and spline regression models. Mean, Median, Standard Deviation, Standard Error, Mean Absolute Percentage Error and Root Mean-Square Error were computed. Any difference between the planar method, SPECT and SPECT-CT and the effective volume was evaluated by means of ANOVA and post-hoc tests. Moreover, planar and SPECT-CT acquisitions were performed in 8 patients with hyperthyroidism, considering relevant percentage differences greater than > 20 % from CT gold standard. Results: Concerning phantom studies, the planar method shows higher values of each parameter than the other two methods. SPECT-CT shows lower variability. However, no significant differences were observed between SPECT and SPECT-CT measurements. In patients, relevant differences were found in 7 out of 9 lesions with the planar method, in 6 lesions with SPECT, but in only one with SPECT-CT. Conclution: Our study confirms the superiority of SPECT in volume measurement if compared with the planar method. A more accurate measurement can be obtained from SPECT-CT.

Yttrium-90 TOF-PET-Based EUD Predicts Response Post Liver Radioembolizations Using Recommended Manufacturer FDG Reconstruction Parameters

PurposeExplaining why 90Y TOF-PET based equivalent uniform dose (EUD) using recommended manufacturer FDG reconstruction parameters has been shown to predict response.MethodsThe hot rods insert of a Jaszczak deluxe phantom was partially filled with a 2.65 GBq 90Y - 300ml DTPA water solution resulting in a 100 Gy mean absorbed dose in the 6 sectors. A two bed 20min/position acquisition was performed on a 550ps- and on a 320ps- TOF-PET/CT and reconstructed with recommended manufacturer FDG reconstruction parameters, without and with additional filtering. The whole procedure was repeated on both PET after adding 300ml of water (50Gy setup). The phantom was acquired again after decay by a factor of 10 (5Gy setup), but with 200min per bed position. For comparison, the phantom was also acquired with 18F activity corresponding to a clinical FDG whole body acquisition.ResultsThe 100Gy-setup provided a hot rod sectors image almost as good as the 18F phantom. However, despite acquisition time compensation, the 5Gy-setup provides much lower quality imaging. TOF-PET based sectors EUDs for the three large rod sectors agreed with the actual EUDs computed with a radiosensitivity of 0.021Gy-1 well in the range observed in external beam radiotherapy (EBRT), i.e. 0.01-0.04Gy-1. This agreement explains the reunification of the dose-response relationships of the glass and resin spheres in HCC using the TOF-PET based EUD. Additional filtering reduced the EUDs agreement quality.ConclusionsRecommended manufacturer FDG reconstruction parameters are suitable in TOF-PET post 90Y liver radioembolization for accurate tumour EUD computation. The present results rule out the use of low specific activity phantom studies to optimize reconstruction parameters.

Synthetic Antiferromagnetic Gold Nanoparticles as Bimodal Contrast Agents in MRI and CT—An Experimental In Vitro and In Vivo Study

The use of multimodal contrast agents can potentially overcome the intrinsic limitations of individual imaging methods. We have validated synthetic antiferromagnetic nanoparticles (SAF-NPs) as bimodal contrast agents for in vitro cell labeling and in vivo cell tracking using magnetic resonance imaging (MRI) and computed tomography (CT). SAF-NP-labeled cells showed high contrast in MRI phantom studies (r2* = 712 s−1 mM−1), while pelleted cells showed clear contrast enhancement in CT. After intravenous SAF-NP injection, nanoparticles accumulated in the liver and spleen, as visualized in vivo by significant MRI contrast enhancement. Intravenous injection of SAF-NP-labeled cells resulted in cell accumulation in the lungs, which was clearly detectable by using CT but not by using MRI. SAF-NPs proved to be very efficient cell labeling agents for complementary MRI- and CT-based cell tracking. Bimodal monitoring of SAF-NP labeled cells is in particular of interest for applications where the applied imaging methods are not able to visualize the particles and/or cells in all organs.

Diagnostic performance of tomosynthesis for evaluation of bone tumors and tumor-like lesions: a comparison with radiography

Background Even though radiologic diagnosis of bone tumors and tumor-like lesions is usually based on radiographs, radiographically faint imaging features sometimes remain challenging due to overlapping anatomical structures. Purpose To compare tomosynthesis with radiography for the evaluation of bone tumors and tumor-like lesions. Material and Methods Forty-seven bone tumors and tumor-like lesions were assessed with radiographs and tomosynthesis images. Two radiologists independently analyzed imaging features of lesions, including margin, periosteal reaction, cortical thinning, matrix mineralization, cortical destruction (such as pathologic fracture), and extraosseous soft-tissue extension. Computed tomography (CT) imaging was used as a reference method. Diagnostic performances of radiography and tomosynthesis were analyzed and compared based on sensitivity, specificity, accuracy, positive predictive value, and negative predictive value. Effective radiation dose was compared among the three imaging modalities by phantom studies. Results Inter-observer variability (kappa value) for imaging features was slight to moderate on radiography (0.167–0.588), whereas it was nearly perfect on tomosynthesis (0.898–1.000) except for extraosseous soft-tissue extension (0.647 vs. 0.647). Tomosynthesis showed significantly higher sensitivity than radiography in evaluating the margin for bone tumors or tumor-like lesions (1.00 vs. 0.85; P = 0.016), and significantly higher accuracy than radiography in evaluating the margin and matrix mineralization for those (1.00 vs. 0.85; P = 0.016 and 0.91 vs.0.77; P = 0.023, respectively). In phantom studies, mean effective radiation doses were highest in order of CT, tomography, and radiography. Conclusion Tomosynthesis increases sensitivity and accuracy of the margin as well as accuracy of the matrix mineralization of bone tumors and tumor-like lesions compared to radiography.

Inadvertent Detachment of Stent Retrievers during Mechanical Thrombectomy—A Clinical and Biomechanical Perspective

Background: The inadvertent detachment of stent retrievers during mechanical thrombectomy is an extremely rare but feared complication associated with poor clinical outcomes. We discuss management considerations after an unexpected disconnection of the pRESET stent retriever during mechanical thrombectomy, based on clinical experience and mechanical and phantom studies. Methods: We present a clinical course of rare accidents of stent-retriever separation inside an intracranial vessel that occurred in patients in a comprehensive stroke centre between 2018 and 2020. We designed a phantom study to assess the Tigertriever’s ability to remove a detached stent retriever from intercranial vessels. In the mechanical study, several types of stent retrievers were evaluated in order to find the weakest point at which detachment occurred. Results: Two patients (~0.7%) with inadvertent stent-retriever detachment were found in our database. Failed attempts of endovascular removal with no recanalization at the end of procedure were reported in both cases. mRS after 3 months was three and four respectively. In the mechanical study, the Tigertriever was the most resistant to detachment and was followed by Embotrap > pRESET > 3D Separator. In the phantom study, the pRESET device detached in a configuration resembling the M1 segment was successfully removed with the Tigertriever. Conclusions: Conservative management of the inadvertent detachment of stent retrievers during mechanical thrombectomy in large vessel occlusion may be acceptable in order to avoid further periprocedural complications after unsuccessful device removal attempts. Based on the phantom and mechanical studies, the Tigertriever may be a useful tool for the removal of detached pRESET devices.

Optimization of Image Quality in Paediatric Computed Tomography

In this study the effects of ASIR™ and collimation on CT image quality (IQ) parameters were quantified. Catphan®600 phantom studies were performed on a GE HD750 64-slice scanner to investigate the impact of collimation 0.625mm vs. 5mm on the overall IQ. For noise and dose reduction ASIR™ was tested on 0.625mm collimation. The varying %ASIR™, scanned at 150mA and variable kVp and 50% ASIR™ compared to FBP on wide kVp/mA range was used. Image noise, CT# accuracy and uniformity, spatial and contrast resolution, MTF, CNR and Wiener spectrum analysis were performed on 0.625mmAX slices, 5mmAXMPR and 2mmCORMPR. Incremental advantages and disadvantages were seen with stepwise increase in %ASIR™. The 50% ASIR™ was found to be optimal blend for diagnostic quality and has potential for dose reduction in paediatric CT. This quantitative data could be used to design ASIR™-enhanced protocols with consideration of diagnostic task, balancing image quality and radiation dose.

Optimization of Image Quality in Paediatric Computed Tomography

In this study the effects of ASIR™ and collimation on CT image quality (IQ) parameters were quantified. Catphan®600 phantom studies were performed on a GE HD750 64-slice scanner to investigate the impact of collimation 0.625mm vs. 5mm on the overall IQ. For noise and dose reduction ASIR™ was tested on 0.625mm collimation. The varying %ASIR™, scanned at 150mA and variable kVp and 50% ASIR™ compared to FBP on wide kVp/mA range was used. Image noise, CT# accuracy and uniformity, spatial and contrast resolution, MTF, CNR and Wiener spectrum analysis were performed on 0.625mmAX slices, 5mmAXMPR and 2mmCORMPR. Incremental advantages and disadvantages were seen with stepwise increase in %ASIR™. The 50% ASIR™ was found to be optimal blend for diagnostic quality and has potential for dose reduction in paediatric CT. This quantitative data could be used to design ASIR™-enhanced protocols with consideration of diagnostic task, balancing image quality and radiation dose.

Monte Carlo and Tissue-Phantom studies of Photoacoustic Imaging of Carotid Intraplaque Haemorrhage

Strokes are the second leading cause of death worldwide. Vulnerable carotid plaques are a primary cause of stroke, with carotid Intraplaque Haemmorrghages being a key feature of vulnerability. MR imaging, which is sensitive to the presence of endogenous Methemoglobin (MetHb), is used to detect IPH. MRI is however expensive, and not readily available. We propose the use of Photoacoustic Imaging (PAI) for the detection of IPH, with MetHb being the primary PA imaging target. I examine the feasibility of this approach by performing Monte Carlo studies of light propagation, energy deposition and PA generation in tissuemimicking models, as well as experimental PA measurements of MetHb in tissue-mimicking phantoms. I show that is possible to achieve an SNR of ∼50dB at the average carotid artery depth of ∼21mm, with the possibility of imaging up to ≥ 32mm in Type I skin using commonly available hardware.