The role of preclinical SPECT in oncological and neurological research in combination with either CT or MRI

Feasibility of Imaging Small Animals on a 360° Whole-Body Cadmium Zinc Telluride SPECT Camera: a Phantom Study

PURPOSE

Single-photon emission computed tomography has found an important place in preclinical cancer research. Nevertheless, the cameras dedicated to small animals are not widely available. The present study aimed to assess the feasibility of imaging small animals by a newly released 360° cadmium zinc telluride camera (VERITON, Spectrum Dynamics, Israel) dedicated to human patients.

PROCEDURES

A cylindrical phantom containing hot spheres was used to evaluate the intrinsic performance of the camera first without the presence of background activity and then with two contrasts between background and hot spheres (1/4 and 1/10). Acquisitions were repeated with different scan durations (10 and 20 min), two tested radioisotopes (Tc-99 m and I-123), and a set of reconstruction parameters (10 iterations [i] 8 subsets [s], 10i16s, 10i32s). A 3D-printed phantom mimicking a rat with four subcutaneous tumours was then used to test the camera under preclinical conditions.

RESULTS

The results obtained from the micro-hollow sphere phantom showed that it was possible to visualize spheres with an inner diameter of 3.95 mm without background activity. Moreover, spheres with diameters of 4.95 mm can be seen in the condition of high contrast between background and spheres (1/10) and 7.86 mm with lower contrast (1/4). The rat-sized phantom acquisitions showed that 10- and 8-mm subcutaneous tumours were visible with a good contrast obtained for the two radioisotopes tested in this study. Both Tc-99 m and I-123 measurements demonstrated that a 10-min acquisition reconstructed with an ordered subset expectation maximization algorithm applying 10i32s was optimal to obtain sufficient image quality in terms of noise, resolution, and contrast.

CONCLUSION

Phantom results showed the ability of the system to detect sub-centimetre lesions for various radioisotopes. It seemed feasible to image small animals using a 360° cadmium zinc telluride gamma camera for preclinical cancer research purposes.

Experimental evaluation of absolute quantification in 99m Tc-TRODAT-1 SPECT/CT brain dopamine transporter (DAT) studies

Objective

To evaluate the quantitative accuracy of clinical brain dopamine transporters (DAT) investigations utilizing ^99mTc‐TRODAT‐1 single‐photon emission computed tomography (SPECT)/computed tomography (CT) in experimental and clinical settings.

Materials and methods

The study used an experimental phantom evaluation and a clinical dataset. Three‐dimensional‐ordered subsets expectation–maximization reconstructed the original and resampled datasets using attenuation correction, scatter correction, and resolution recovery. The reconstructed data were analyzed and reported as percentage difference, standardized uptake value reference (SUVr), and a coefficient of variation (CoV). The Taguchi method tested the impact of the three different parameters on signal‐to‐noise ratio (SNR) and SUVr, including number iteration, Poisson resampling, and phantom setup, with and without the plaster of Paris (POP). Six ^99mTc‐TRODAT‐1 SPECT/CT scans were acquired in healthy subjects for verification purposes.

Results

The percentage activity difference between the phantom with and without POP is 20% and 5%, respectively. The SUVr reveals a 10% underestimate for both with and without POP. When it comes to the influence of Poisson resampling, the SUVr value for 75% Poisson resampling indicates 10% underestimation on both sides of the caudate and putamen area, with and without POP. When 25% of Poisson resampling is applied, the SUVr value is overestimated (±35%). In the Taguchi analysis, iteration numbers were the most dominant factor with the F‐value of 9.41 and the contribution rate of 52.66% (p < 0.05) for SNR. In comparison, F‐value of 9.1 for Poisson resampled with contribution rate of 58.91% (p < 0.05) for SUVr. Reducing counts by 25% from the original dataset resulted in a minimal bias in SUVr, compared to 50% and 75%.

Conclusion

The optimal absolute SPECT/CT quantification of brain DAT studies using ^99mTc‐TRODAT‐1 appears achievable with at least 4i10s and SUVr as the surrogate parameter. In clinical investigations, it is possible to reduce the recommended administered dose by up to 25% while maintaining accurate measurement.

Assessment of mouse-specific pharmacokinetics in kidneys based on 131I activity measurements using micro-SPECT

BACKGROUND

In order to acquire accurate drug pharmacokinetic information, which is required for tissue dosimetry, micro-SPECT must be quantitative to allow for an accurate assessment of radioligand activity in the relevant tissue. This study investigates the feasibility of deriving accurate mouse-specific time-integrated drug pharmacokinetic data in mouse kidneys from activity measurements using micro-SPECT.

METHODS

An animal experiment was carried out to evaluate the accuracy of ¹³¹I activity quantification in mouse kidneys (mean tissue volume of 0.140 mL) using a micro-SPECT system against conventional ex vivo gamma counting (GC) in a NaI(Tl) detector. The imaging setting investigated was that of the mouse biodistribution of a ¹³¹I-labelled single-domain antibody fragment (sdAb), currently being investigated for targeted radionuclide therapy of HER2-expressing cancer. SPECT imaging of ¹³¹I 365-keV photons was done with a VECTor/CT system (MILabs, Netherlands) using a high-energy mouse collimator with 1.6-mm-diameter pinholes. For both activity quantification techniques, the pharmacokinetic profile of the radioligand from approximately 1-73 h p.i. was derived and the time-integrated activity coefficient per gram of tissue (ã/M) was estimated. Additionally, SPECT activity recovery coefficients were determined in a phantom setting.

RESULTS

SPECT activities underestimate the reference activities by an amount that is dependent on the ¹³¹I activity concentration in the kidney, and thus on the time point of the pharmacokinetic profile. This underestimation is around - 12% at 1.5 h (2.89 MBq mL^-1 mean reference activity concentration), - 13% at 6.6 h (149 kBq mL^-1), - 40% at 24 h (17.6 kBq mL^-1) and - 46% at 73 h (5.2 kBq mL^-1) p.i. The ã/M value estimated from SPECT activities is, nevertheless, within - 14% from the reference (GC) ã/M value. Furthermore, better quantitative accuracy (within 2% from GC) in the SPECT ã/M value is achieved when SPECT activities are compensated for partial recovery with a phantom-based recovery coefficient of 0.85.

CONCLUSION

The SPECT imaging system used, together with a robust activity quantification methodology, allows an accurate estimation of time-integrated pharmacokinetic information of the ¹³¹I-labelled sdAb in mouse kidneys. This opens the possibility to perform mouse-specific kidney-tissue dosimetry based on pharmacokinetic data acquired in vivo on the same mice used in nephrotoxicity studies.

Protein Based Biomaterials for Therapeutic and Diagnostic Applications

Proteins are some of the most versatile and studied macromolecules with extensive biomedical applications. The natural and biological origin of proteins offer such materials several advantages over their synthetic counterparts, such as innate bioactivity, recognition by cells and reduced immunogenic potential. Furthermore, proteins can be easily functionalized by altering their primary amino acid sequence and can often be further self-assembled into higher order structures either spontaneously or under specific environmental conditions. This review will feature the recent advances in protein-based biomaterials in the delivery of therapeutic cargo such as small molecules, genetic material, proteins, and cells. First, we will discuss the ways in which secondary structural motifs, the building blocks of more complex proteins, have unique properties that enable them to be useful for therapeutic delivery. Next, supramolecular assemblies, such as fibers, nanoparticles, and hydrogels, made from these building blocks that are engineered to behave in a cohesive manner, are discussed. Finally, we will cover additional modifications to protein materials that impart environmental responsiveness to materials. This includes the emerging field of protein molecular robots, and relatedly, protein-based theranostic materials that combine therapeutic potential with modern imaging modalities, including near-infrared fluorescence spectroscopy (NIRF), single-photo emission computed tomography/computed tomography (SPECT/CT), positron emission tomography (PET), magnetic resonance imaging (MRI), and ultrasound/photoacoustic imaging (US/PAI).

Classification of the Multiple Stages of Parkinson's Disease by a Deep Convolution Neural Network Based on 99mTc-TRODAT-1 SPECT Images

Single photon emission computed tomography (SPECT) has been employed to detect Parkinson's disease (PD). However, analysis of the SPECT PD images was mostly based on the region of interest (ROI) approach. Due to limited size of the ROI, especially in the multi-stage classification of PD, this study utilizes deep learning methods to establish a multiple stages classification model of PD. In the retrospective study, the 99mTc-TRODAT-1 was used for brain SPECT imaging. A total of 202 cases were collected, and five slices were selected for analysis from each subject. The total number of images was thus 1010. According to the Hoehn and Yahr Scale standards, all the cases were divided into healthy, early, middle, late four stages, and HYS I~V six stages. Deep learning is compared with five convolutional neural networks (CNNs). The input images included grayscale and pseudo color of two types. The training and validation sets were 70% and 30%. The accuracy, recall, precision, F-score, and Kappa values were used to evaluate the models' performance. The best accuracy of the models based on grayscale and color images in four and six stages were 0.83 (AlexNet), 0.85 (VGG), 0.78 (DenseNet) and 0.78 (DenseNet).

In vivo quantification of mandibular bone remodeling and vascular changes in a Wistar rat model: A novel HR-MRI and micro-CT fusion technique

Purpose

This study was performed to introduce an in vivo hybrid multimodality technique involving the coregistration of micro-computed tomography (micro-CT) and high-resolution magnetic resonance imaging (HR-MRI) to concomitantly visualize and quantify mineralization and vascularization at follow-up in a rat model.

Materials and Methods

Three adult female rats were randomly assigned as test subjects, with 1 rat serving as a control subject. For 20 weeks, the test rats received a weekly intravenous injection of 30 µg/kg zoledronic acid, and the control rat was administered a similar dose of normal saline. Bilateral extraction of the lower first and second molars was performed after 10 weeks. All rats were scanned once every 4 weeks with both micro-CT and HR-MRI. Micro-CT and HR-MRI images were registered and fused in the same 3-dimensional region to quantify blood flow velocity and trabecular bone thickness at T0 (baseline), T4 (4 weeks), T8 (8 weeks), T12 (12 weeks), T16 (16 weeks), and T20 (20 weeks). Histological assessment was the gold standard with which the findings were compared.

Results

The histomorphometric images at T20 aligned with the HR-MRI findings, with both test and control rats demonstrating reduced trabecular bone vasculature and blood vessel density. The micro-CT findings were also consistent with the histomorphometric changes, which revealed that the test rats had thicker trabecular bone and smaller marrow spaces than the control rat.

Conclusion

The combination of micro-CT and HR-MRI may be considered a powerful non-invasive novel technique for the longitudinal quantification of localized mineralization and vascularization.

Guidelines for the experimental design of pharmacokinetic studies with nanomaterials in preclinical animal models

A shared feature in the value proposition of every nanomaterial-based drug delivery systems is the desirable improvement in the disposition (or ADME) and pharmacokinetic profiles of the encapsulated drug being delivered. Remarkable progress has been made towards understanding the complex and multifactorial relationships between pharmacokinetic profiles and nanomaterial physicochemical properties, biological interactions, species physiology, etc. These advances have fuelled the rational design of numerous nanomaterials with long-circulation times and improved tissue accumulation (e.g., in tumours). Unfortunately, a central weakness in many of these research efforts has been the inconsistent and insufficient characterisation of the pharmacokinetic profiles of nanomaterials in scientific reporting-a problem affecting the majoirty of of contemporary nanomaterials literature and innovative nanomaterials in early stages of preclinical development especially. Given the significant role of pharmacokinetic assessments to serve as guideposts for deciding whether to continue with the preclinical development and clinical translation of drug delivery systems, the prevalence of poor pharmacokinetic characterisations in nanomaterials research is particularly alarming. A conspicuous problem in many reports is the inappropriate selection of experimental designs and methodologies for studying nanomaterial pharmacokinetics, the consequences of which are increased uncertainty over the accurate interpretation of reported pharmacokinetic data and diminished experimental reproducibility throughout the field. Thus, there is renewed interest in the establishment of consistent and comprehensive strategies for designing preclinical experiments to assess the pharmacokinetics of nanomaterials with diverse physicochemical properties. Towards this end, herein are proposed simple guidelines for the experimental design of pharmacokinetic studies with nanomaterials drawn from the best research practices, principle strategies, and important considerations used in industry for collecting pharmacokinetic data in preclinical animal models. Specifically, key experimental design factors in these studies are identified and examined in the context of nanomaterials for optimality, including blood sampling strategy and technique, sample allocation and sampling time window, test species selection, experimental sources of pharmacokinetic variability, etc. Methods for noninvasive imaging-derived pharmacokinetic assessments of theranostic nanomaterials are also explored with particular focus on emission tomography imaging modalities. Taken together, this review will provide nanomaterial researchers with practical knowledge and pragmatic recommendations for selecting the best designs and methodologies for assessing the pharmacokinetic profiles of their nanomaterials, and hopefully maximise the chances of translational success of these innovative products into humans.

Imaging of Red-Shifted Light From Bioluminescent Tumors Using Fluorescence by Unbound Excitation From Luminescence

Early detection of tumors is today a major challenge and requires sensitive imaging methodologies coupled with new efficient probes. In vivo optical bioluminescence imaging has been widely used in the field of preclinical oncology to visualize tumors and several cancer cell lines have been genetically modified to provide bioluminescence signals. However, the light emitted by the majority of commonly used luciferases is usually in the blue part of the visible spectrum, where tissue absorption is still very high, making deep tissue imaging non-optimal, and calling for optimized optical imaging methodologies. We have previously shown that red-shifting of bioluminescence signal by Fluorescence Unbound Excitation from Luminescence (FUEL) is a mean to increase bioluminescence signal sensitivity detection in vivo. Here, we applied FUEL to tumor detection in two different subcutaneous tumor models: the auto-luminescent human embryonic kidney (HEK293) cell line and the murine B16-F10 melanoma cell line previously transfected with a plasmid encoding the Luc2 firefly luciferase. Tumor size and bioluminescence were measured over time and tumor vascularization characterized. We then locally injected near infrared emitting Quantum Dots (NIR QDs) in the tumor site and observed a red-shifting of bioluminescence signal by (FUEL) indicating that FUEL could be used to allow deeper tumor detection in mice.

In Vivo Imaging With Confirmation by Histopathology for Increased Rigor and Reproducibility in Translational Research: A Review of Examples, Options, and Resources

Preclinical noninvasive imaging can be an indispensable tool for studying animal models of disease. In vivo imaging to assess anatomical, functional, and molecular features requires verification by a comparison to the macroscopic and microscopic morphological features, since all noninvasive in vivo imaging methods have much lower resolution than standard histopathology. Comprehensive pathological evaluation of the animal model is underutilized; yet, many institutions have veterinary or human pathologists with necessary comparative pathology expertise. By performing a rigorous comparison to gross or histopathology for image interpretation, these trained individuals can assist scientists with the development of the animal model, experimental design, and evaluation of the in vivo imaging data. These imaging and pathology corroboration studies undoubtedly increase scientific rigor and reproducibility in descriptive and hypothesis-driven research. A review of case examples including ultrasound, nuclear, optical, and MRI is provided to illustrate how a wide range of imaging modalities data can be confirmed by gross or microscopic pathology. This image confirmation and authentication will improve characterization of the model and may contribute to decreasing costs and number of animals used and to more rapid translation from preclinical animal model to the clinic.

Regulatory Forum Opinion Piece*: Imaging Applications in Toxicologic Pathology-Recommendations for Use in Regulated Nonclinical Toxicity Studies

Available imaging systems for use in preclinical toxicology studies increasingly show utility as important tools in the toxicologic pathologist's armamentarium, permit longitudinal evaluation of functional and morphological changes in tissues, and provide important information such as organ and lesion volume not obtained by conventional toxicology study parameters. Representative examples of practical imaging applications in toxicology research and preclinical studies are presented for ultrasound, positron emission tomography/single-photon emission computed tomography, optical, magnetic resonance imaging, and matrix-assisted laser desorption ionization-imaging mass spectrometry imaging. Some of the challenges for making imaging systems good laboratory practice-compliant for regulatory submission are presented. Use of imaging data on a case-by-case basis as part of safety evaluation in regulatory submissions is encouraged.

Estimation of subject coregistration errors during multimodal preclinical imaging using separate instruments: origins and avoidance of artifacts

We use high-resolution [Formula: see text] data in multiple experiments to estimate the sources of error during coregistration of images acquired on separate preclinical instruments. In combination with experiments with phantoms, we completed in vivo imaging on mice, aimed at identifying the possible sources of registration errors, caused either by transport of the animal, movement of the animal itself, or methods of coregistration. The same imaging cell was used as a holder for phantoms and animals. For all procedures, rigid coregistration was carried out using a common landmark coregistration system, placed inside the imaging cell. We used the fiducial registration error and the target registration error to analyze the coregistration accuracy. We found that moving an imaging cell between two preclinical devices during a multimodal procedure gives an error of about [Formula: see text] at most. Therefore, it could not be considered a source of coregistration errors. Errors linked to spontaneous movements of the animal increased with time, to nearly 1 mm at most, excepted for body parts that were properly restrained. This work highlights the importance of animal intrinsic movements during a multiacquisition procedure and demonstrates a simple method to identify and quantify the sources of error during coregistration.

Longitudinal imaging of the ageing mouse

Several non-invasive imaging techniques are used to investigate the effect of pathologies and treatments over time in mouse models. Each preclinical in vivo technique provides longitudinal and quantitative measurements of changes in tissues and organs, which are fundamental for the evaluation of alterations in phenotype due to pathologies, interventions and treatments. However, it is still unclear how these imaging modalities can be used to study ageing with mice models. Almost all age related pathologies in mice such as osteoporosis, arthritis, diabetes, cancer, thrombi, dementia, to name a few, can be imaged in vivo by at least one longitudinal imaging modality. These measurements are the basis for quantification of treatment effects in the development phase of a novel treatment prior to its clinical testing. Furthermore, the non-invasive nature of such investigations allows the assessment of different tissue and organ phenotypes in the same animal and over time, providing the opportunity to study the dysfunction of multiple tissues associated with the ageing process. This review paper aims to provide an overview of the applications of the most commonly used in vivo imaging modalities used in mouse studies: micro-computed-tomography, preclinical magnetic-resonance-imaging, preclinical positron-emission-tomography, preclinical single photon emission computed tomography, ultrasound, intravital microscopy, and whole body optical imaging.

CT perfusion with acetazolamide challenge in C6 gliomas and angiogenesis

Background

This study was performed to investigate the correlation between CT perfusion with acetazolamide challenge and angiogenesis in C6 gliomas.

Methods

Thirty-two male Sprague-Dawley rats were evaluated. The rats were divided randomly to four groups: eight rats with orthotopically implanted C6 gliomas at 10-days old (Group A), eight rats with gliomas at 14-days old (Group B), eight rats with gliomas at 18-days old (Group C), eight rats with orthotopically injected normal saline served as controls. CT perfusion was performed before and after administration of acetazolamide. Changes in perfusion parameters due to acetazolamide administration were calculated and analyzed.

Results

Elevated carbon dioxide partial pressure and decreased pH were found in all 32 rats post acetazolamide challenge (P<0.01). Cerebral blood flow_{pre-challenge} was increased in group C (95.0±2.5 ml/100g/min), as compared to group B (80.1±11.3 ml/100g/min) and group A (63.1±2.1 ml/100g/min). Cerebral blood flow percentage changes were detected with a reduction in group C (54.2±4.8%) as compared to controls (111.3±22.2%). Cerebral blood volume _{pre-challenge} was increased in group C (50.8±1.7ml/100g), as compared to group B (45.7±1.9 ml/100g) and group A (38.2±0.8 ml/100g). Cerebral blood volume percentage changes were decreased in group C (23.5±4.6%) as compared to controls (113.5±30.4%). Angiogenesis ratio = [(CD105-MVD) / (FVIII-MVD)] ×100%. Positive correlations were observed between CD105-microvessel density, angiogenesis ratio, vascular endothelial growth factor, proliferation marker and cerebral blood flow_{pre-challenge}, cerebral blood volume _{pre-challenge}. Negative correlations were observed between CD105-microvessel density and cerebral blood flow percentage changes (P<0.01, correlation coefficient r=-0.788), cerebral blood volume percentage changes (P<0.01, r=-0.703). Negative correlations were observed between angiogenesis ratio, vascular endothelial growth factor, proliferation marker and cerebral blood flow percentage changes, cerebral blood volume percentage changes.

Conclusion

Our findings suggest that CT perfusion with challenge can provide new insight into non-invasive assessment of rat C6 glioma angiogenesis.

Biomarkers in preclinical cancer imaging

In view of the trend towards personalized treatment strategies for (cancer) patients, there is an increasing need to noninvasively determine individual patient characteristics. Such information enables physicians to administer to patients accurate therapy with appropriate timing. For the noninvasive visualization of disease-related features, imaging biomarkers are expected to play a crucial role. Next to the chemical development of imaging probes, this requires preclinical studies in animal tumour models. These studies provide proof-of-concept of imaging biomarkers and help determine the pharmacokinetics and target specificity of relevant imaging probes, features that provide the fundamentals for translation to the clinic. In this review we describe biological processes derived from the “hallmarks of cancer” that may serve as imaging biomarkers for diagnostic, prognostic and treatment response monitoring that are currently being studied in the preclinical setting. A number of these biomarkers are also being used for the initial preclinical assessment of new intervention strategies. Uniquely, noninvasive imaging approaches allow longitudinal assessment of changes in biological processes, providing information on the safety, pharmacokinetic profiles and target specificity of new drugs, and on the antitumour effectiveness of therapeutic interventions. Preclinical biomarker imaging can help guide translation to optimize clinical biomarker imaging and personalize (combination) therapies.

Cancer immunotherapy: nanodelivery approaches for immune cell targeting and tracking

Cancer is one of the most common diseases afflicting people globally. New therapeutic approaches are needed due to the complexity of cancer as a disease. Many current treatments are very toxic and have modest efficacy at best. Increased understanding of tumor biology and immunology has allowed the development of specific immunotherapies with minimal toxicity. It is important to highlight the performance of monoclonal antibodies, immune adjuvants, vaccines and cell-based treatments. Although these approaches have shown varying degrees of clinical efficacy, they illustrate the potential to develop new strategies. Targeted immunotherapy is being explored to overcome the heterogeneity of malignant cells and the immune suppression induced by both the tumor and its microenvironment. Nanodelivery strategies seek to minimize systemic exposure to target therapy to malignant tissue and cells. Intracellular penetration has been examined through the use of functionalized particulates. These nano-particulate associated medicines are being developed for use in imaging, diagnostics and cancer targeting. Although nano-particulates are inherently complex medicines, the ability to confer, at least in principle, different types of functionality allows for the plausible consideration these nanodelivery strategies can be exploited for use as combination medicines. The development of targeted nanodelivery systems in which therapeutic and imaging agents are merged into a single platform is an attractive strategy. Currently, several nanoplatform-based formulations, such as polymeric nanoparticles, micelles, liposomes and dendrimers are in preclinical and clinical stages of development. Herein, nanodelivery strategies presently investigated for cancer immunotherapy, cancer targeting mechanisms and nanocarrier functionalization methods will be described. We also intend to discuss the emerging nano-based approaches suitable to be used as imaging techniques and as cancer treatment options.