Total body CD4+ T cell dynamics in treated and untreated SIV infection revealed by in vivo imaging.

The peripheral blood represents only a small fraction of the total number of lymphocytes in the body. To develop a more thorough understanding of T cell dynamics, including the effects of SIV/SHIV/HIV infection on immune cell depletion and immune reconstitution following combination antiretroviral therapy (cART), one needs to utilize approaches that allow direct visualization of lymphoid tissues. In the present study, noninvasive in vivo imaging of the CD4+ T cell pool has revealed that the timing of the CD4+ T cell pool reconstitution following initiation of ART in SIV-infected nonhuman primates (NHPs) appears seemingly stochastic among clusters of lymph nodes within the same host. At 4 weeks following initiation or interruption of cART, the changes observed in peripheral blood (PB) are primarily related to changes in the whole-body CD4 pool rather than changes in lymphocyte trafficking. Lymph node CD4 pools in long-term antiretroviral-treated and plasma viral load-suppressed hosts appear suboptimally reconstituted compared with healthy controls, while splenic CD4 pools appear similar between the 2 groups.

[18F]-Fluorodeoxyglucose Uptake in Lymphoid Tissue Serves as a Predictor of Disease Outcome in the Nonhuman Primate Model of Monkeypox Virus Infection.

Real-time bioimaging of infectious disease processes may aid countermeasure development and lead to an improved understanding of pathogenesis. However, few studies have identified biomarkers for monitoring infections using in vivo imaging. Previously, we demonstrated that positron emission tomography/computed tomography (PET/CT) imaging with [18F]-fluorodeoxyglucose (FDG) can monitor monkeypox disease progression in vivo in nonhuman primates (NHPs). In this study, we investigated [18F]-FDG-PET/CT imaging of immune processes in lymphoid tissues to identify patterns of inflammation in the monkepox NHP model and to determine the value of [18F]-FDG-PET/CT as a biomarker for disease and treatment outcomes. Quantitative analysis of [18F]-FDG-PET/CT images revealed differences between moribund and surviving animals at two sites vital to the immune response to viral infections, bone marrow and lymph nodes (LNs). Moribund NHPs demonstrated increased [18F]-FDG uptake in bone marrow 4 days postinfection compared to surviving NHPs. In surviving, treated NHPs, increase in LN volume correlated with [18F]-FDG uptake and peaked 10 days postinfection, while minimal lymphadenopathy and higher glycolytic activity were observed in moribund NHPs early in infection. Imaging data were supported by standard virology, pathology, and immunology findings. Even with the limited number of subjects, imaging was able to differentiate the difference between disease outcomes, warranting additional studies to demonstrate whether [18F]-FDG-PET/CT can identify other, subtler effects. Visualizing altered metabolic activity at sites involved in the immune response by [18F]-FDG-PET/CT imaging is a powerful tool for identifying key disease-specific time points and locations that are most relevant for pathogenesis and treatment.IMPORTANCE Positron emission tomography and computed tomography (PET/CT) imaging is a universal tool in oncology and neuroscience. The application of this technology to infectious diseases is far less developed. We used PET/CT imaging with [18F]-labeled fluorodeoxyglucose ([18F]-FDG) in monkeys after monkeypox virus exposure to monitor the immune response in lymphoid tissues. In lymph nodes of surviving monkeys, changes in [18F]-FDG uptake positively correlated with enlargement of the lymph nodes and peaked on day 10 postinfection. In contrast, the bone marrow and lymph nodes of nonsurvivors showed increased [18F]-FDG uptake by day 4 postinfection with minimal lymph node enlargement, indicating that elevated cell metabolic activity early after infection is predictive of disease outcome. [18F]-FDG-PET/CT imaging can provide real-time snapshots of metabolic activity changes in response to viral infections and identify key time points and locations most relevant for monitoring the development of pathogenesis and for potential treatment to be effective.

Modeling [(18)F]-FDG lymphoid tissue kinetics to characterize nonhuman primate immune response to Middle East respiratory syndrome-coronavirus aerosol challenge.

BACKGROUND: The pathogenesis and immune response to Middle East respiratory syndrome (MERS) caused by a recently discovered coronavirus, MERS-CoV, have not been fully characterized because a suitable animal model is currently not available. (18)F-Fluorodeoxyglucose ([(18)F]-FDG)-positron emission tomography/computed tomography (PET/CT) as a longitudinal noninvasive approach can be beneficial in providing biomarkers for host immune response. [(18)F]-FDG uptake is increased in activated immune cells in response to virus entry and can be localized by PET imaging. We used [(18)F]-FDG-PET/CT to investigate the host response developing in nonhuman primates after MERS-CoV exposure and applied kinetic modeling to monitor the influx rate constant (K i ) in responsive lymphoid tissue. METHODS: Multiple [(18)F]-FDG-PET and CT images were acquired on a PET/CT clinical scanner modified to operate in a biosafety level 4 environment prior to and up to 29 days after MERS-CoV aerosol exposure. Time activity curves of various lymphoid tissues were reconstructed to follow the [(18)F]-FDG uptake for approximately 60 min (3,600 s). Image-derived input function was used to calculate K i for lymphoid tissues by Patlak plot. RESULTS: Two-way repeated measures analysis of variance revealed alterations in K i that was associated with the time point (p < 0.001) after virus exposure and the location of lymphoid tissue (p = 0.0004). As revealed by a statistically significant interaction (p < 0.0001) between these two factors, the pattern of K i changes over time differed between three locations but not between subjects. A distinguished pattern of statistically significant elevation in K i was observed in mediastinal lymph nodes (LNs) that correlated to K i changes in axillary LNs. Changes in LNs K i were concurrent with elevations of monocytes in peripheral blood. CONCLUSIONS: [(18)F]-FDG-PET is able to detect subtle changes in host immune response to contain a subclinical virus infection. Full quantitative analysis is the preferred approach rather than semiquantitative analysis using standardized uptake value for detection of the immune response to the virus.

Discordance in lymphoid tissue recovery following stem cell transplantation in rhesus macaques: an in vivo imaging study.

Ionizing irradiation is used routinely to induce myeloablation and immunosuppression. However, it has not been possible to evaluate the extent of ablation without invasive biopsy. For lymphoid recovery, peripheral blood (PB) lymphocytes (PBLs) have been used for analysis, but they represent <2% of cells in lymphoid tissues (LTs). Using a combination of single-photon emission computed tomography imaging and a radiotracer ((99m)Tc-labeled rhesus immunoglobulin G1 anti-CD4R1 (Fab')2), we sequentially imaged CD4(+) cell recovery in rhesus macaques following total body irradiation (TBI) and reinfusion of vector-transduced, autologous CD34(+) cells. Our results present for the first time a sequential, real-time, noninvasive method to evaluate CD4(+) cell recovery. Importantly, despite myeloablation of circulating leukocytes following TBI, total depletion of CD4(+) lymphocytes in LTs such as the spleen is not achieved. The impact of TBI on LTs and PBLs is discordant, in which as few as 32.4% of CD4(+) cells were depleted from the spleen. In addition, despite full lymphocyte recovery in the spleen and PB, lymph nodes have suboptimal recovery. This highlights concerns about residual disease, endogenous contributions to recovery, and residual LT damage following ionizing irradiation. Such methodologies also have direct application to immunosuppressive therapy and other immunosuppressive disorders, such as those associated with viral monitoring.

Nuclear medicine practices in the 1950s through the mid-1970s and occupational radiation doses to technologists from diagnostic radioisotope procedures.

Data on occupational radiation exposure from nuclear medicine procedures for the time period of the 1950s through the 1970s is important for retrospective health risk studies of medical personnel who conducted those activities. However, limited information is available on occupational exposure received by physicians and technologists who performed nuclear medicine procedures during those years. To better understand and characterize historical radiation exposures to technologists, the authors collected information on nuclear medicine practices in the 1950s, 1960s, and 1970s. To collect historical data needed to reconstruct doses to technologists, a focus group interview was held with experts who began using radioisotopes in medicine in the 1950s and the 1960s. Typical protocols and descriptions of clinical practices of diagnostic radioisotope procedures were defined by the focus group and were used to estimate occupational doses received by personnel, per nuclear medicine procedure, conducted in the 1950s to 1960s using radiopharmaceuticals available at that time. The radionuclide activities in the organs of the reference patient were calculated using the biokinetic models described in ICRP Publication 53. Air kerma rates as a function of distance from a reference patient were calculated by Monte Carlo radiation transport calculations using a hybrid computational phantom. Estimates of occupational doses to nuclear medicine technologists per procedure were found to vary from less than 0.01 µSv (thyroid scan with 1.85 MBq of administered I-iodide) to 0.4 µSv (brain scan with 26 MBq of Hg-chlormerodin). Occupational doses for the same diagnostic procedures starting in the mid-1960s but using Tc were also estimated. The doses estimated in this study show that the introduction of Tc resulted in an increase in occupational doses per procedure.

The effect of volume of interest definition on quantification of lymph node immune response to a monkeypox virus infection assessed by (18)F-FDG-PET.

BACKGROUND: 2-deoxy-2-[(18)F]fluoro-D-glucose-positron emission tomography ((18)F-FDG-PET) is applied in the clinic for infection assessment and is under consideration for investigating the inflammatory/immune response in lymphoid tissue in animal models of viral infection. Assessing changes in (18)F-FDG uptake of lymph nodes (LNs), primary lymphoid tissues targeted during viral infection, requires suitable methods for image analysis. Similar to tumor evaluation, reliable quantitation of the LN function via multiple (18)F-FDG-PET sessions will depend how the volume of interest is defined. Volume of interest definition has a direct effect on statistical outcome. The current study objective is to compare for the first time agreement between conventional and modified VOI metrics to determine which method(s) provide(s) reproducible standardized uptake values (SUVs) for (18)F-FDG uptake in the LN of rhesus macaques. METHODS: Multiple (18)F-FDG-PET images of LNs in macaques were acquired prior to and after monkeypox virus intravenous inoculation. We compared five image analysis approaches, SUVmax, SUVmean, SUVthreshold, modified SUVthreshold, and SUVfixed volume, to investigate the impact of these approaches on quantification of the changes in LN metabolic activity denoting the immune response during viral infection progression. RESULTS: The lowest data repeatability was observed with SUVmax. The best correspondence was between SUVfixed volume and conventional and modified SUVthreshold. A statistically significant difference in the LN (18)F-FDG uptake between surviving and moribund animals was shown using modified SUVthreshold and SUVfixed volume (adjusted p = 0.0037 and p = 0.0001, respectively). CONCLUSIONS: Quantification of the LN (18)F-FDG uptake is highly sensitive to the method applied for PET image analysis. SUVfixed volume and modified SUVthreshold demonstrate better reproducibility for SUV estimates than SUVmax, SUVmean, and SUVthreshold. SUVfixed volume and modified SUVthreshold are capable of distinguishing between groups with different disease outcomes. Therefore, these methods are the preferred approaches for evaluating the LN function during viral infection by (18)F-FDG-PET. Validation of multiple approaches is necessary to choose a suitable method to monitor changes in LN metabolic activity during progression of viral infection.

Progress using Tc-99m radiopharmaceuticals for measuring high capacity sites and low density sites.

Technetium-99m (Tc-99m) has long been a mainstay in clinical nuclear medicine, primarily monitoring biological processes in the heart, kidney, liver, and brain. More recently, Tc-99m chelates have been used as the reporter in targeted nuclear medicine probes that monitor changes in specific protein expression products. The strengths remain the inexpensive source of Tc-99m from the Mo-99/Tc-99m generator, its rich chemistry, high-yield kit formulation, and its widespread availability. Hardware and software advances, such as OSEM reconstructions with scatter and attenuation corrections, have led to quantitation of the injected radioactivity in terms of kBq/cm.

Evaluation of monkeypox disease progression by molecular imaging.

Infection of nonhuman primates (NHPs) with monkeypox virus (MPXV) is currently being developed as an animal model of variola infection in humans. We used positron emission tomography and computed tomography (PET/CT) to identify inflammatory patterns as predictors for the outcome of MPXV disease in NHPs. Two NHPs were sublethally inoculated by the intravenous (IV) or intrabronchial (IB) routes and imaged sequentially using fluorine-18 fluorodeoxyglucose ((18)FDG) uptake as a nonspecific marker of inflammation/immune activation. Inflammation was observed in the lungs of IB-infected NHPs, and bilobular involvement was associated with morbidity. Lymphadenopathy and immune activation in the axillary lymph nodes were evident in IV- and IB-infected NHPs. Interestingly, the surviving NHPs had significant (18)FDG uptake in the axillary lymph nodes at the time of MPXV challenge with no clinical signs of illness, suggesting an association between preexisting immune activation and survival. Molecular imaging identified patterns of inflammation/immune activation that may allow risk assessment of monkeypox disease.

Gamma probes and their use in tumor detection in colorectal cancer.

The purpose of this article is to summarize the role of gamma probes in intraoperative tumor detection in patients with colorectal cancer (CRC), as well as provide basic information about the physical and practical characteristics of the gamma probes, and the radiopharmaceuticals used in gamma probe tumor detection. In a significant portion of these studies, radiolabeled monoclonal antibodies (Mabs), particularly 125I labeled B72.3 Mab that binds to the TAG-72 antigen, have been used to target tumor. Studies have reported that intraoperative gamma probe radioimmunodetection helps surgeons to localize primary tumor, clearly delineate its resection margins and provide immediate intraoperative staging. Studies also have emphasized the value of intraoperative gamma probe radioimmunodetection in defining the extent of tumor recurrence and finding sub-clinical occult tumors which would assure the surgeons that they have completely removed the tumor burden. However, intraoperative gamma probe radioimmunodetection has not been widely adapted among surgeons because of some constraints associated with this technique. The main difficulty with this technique is the long period of waiting time between Mab injection and surgery. The technique is also laborious and costly. In recent years, Fluorine-18-2-fluoro-2-deoxy-D-glucose (18F-FDG) use in gamma probe tumor detection surgery has renewed interest among surgeons. Preliminary studies during surgery have demonstrated that use of FDG in gamma probe tumor detection during surgery is feasible and useful.

Targeted imaging: an important biomarker for understanding disease progression in the era of personalized medicine.

The key to applying targeted imaging to personalized medicine is the choice of the right radiolabeled probe for the right target for the right disease following the lead of pharmaceutical development. The imaging approach differs depending on whether the target is a single disease control point (e.g. a specific receptor or transport protein linked to the mechanistic activity of a drug) or a general disease control point applicable to a number of treatment paradigms (e.g. proliferation, angiogenesis, inflammation). But in either case, the number of control points must be small given the time constraints on molecular imaging procedures in the clinic. Regardless of the choice, the radiotracer must be validated as binding to the target with the appropriate pharmacokinetics and pharmacodynamics for effective external imaging. Such an imaging agent developed in concert with drug development has a built in synergy that will accelerate the drug development process, targeted imaging and personalized medicine as well.

Positron emission tomography in the diagnosis and management of giant cell arteritis.

We describe a 58-year-old woman who presented with new onset of temporal headaches and a nondiagnostic temporal artery biopsy in whom positron emission tomography led to the diagnosis of giant cell arteritis. After treatment with corticosteroids the patient's symptoms resolved. A repeat (18)FDG PET-CT scan illustrated virtually complete resolution of the abnormal (18)FDG uptake in the arterial wall.

Hypoxia: importance in tumor biology, noninvasive measurement by imaging, and value of its measurement in the management of cancer therapy.

PURPOSE: The Cancer Imaging Program of the National Cancer Institute convened a workshop to assess the current status of hypoxia imaging, to assess what is known about the biology of hypoxia as it relates to cancer and cancer therapy, and to define clinical scenarios in which in vivo hypoxia imaging could prove valuable. RESULTS: Hypoxia, or low oxygenation, has emerged as an important factor in tumor biology and response to cancer treatment. It has been correlated with angiogenesis, tumor aggressiveness, local recurrence, and metastasis, and it appears to be a prognostic factor for several cancers, including those of the cervix, head and neck, prostate, pancreas, and brain. The relationship between tumor oxygenation and response to radiation therapy has been well established, but hypoxia also affects and is affected by some chemotherapeutic agents. Although hypoxia is an important aspect of tumor physiology and response to treatment, the lack of simple and efficient methods to measure and image oxygenation hampers further understanding and limits their prognostic usefulness. There is no gold standard for measuring hypoxia; Eppendorf measurement of pO(2) has been used, but this method is invasive. Recent studies have focused on molecular markers of hypoxia, such as hypoxia inducible factor 1 (HIF-1) and carbonic anhydrase isozyme IX (CA-IX), and on developing noninvasive imaging techniques. CONCLUSIONS: This workshop yielded recommendations on using hypoxia measurement to identify patients who would respond best to radiation therapy, which would improve treatment planning. This represents a narrow focus, as hypoxia measurement might also prove useful in drug development and in increasing our understanding of tumor biology.

Incorporation of SPECT bone marrow imaging into intensity modulated whole-pelvic radiation therapy treatment planning for gynecologic malignancies.

BACKGROUND AND PURPOSE: To incorporate single-photon emission computed tomography (SPECT) bone marrow (BM) imaging into the treatment planning process to reduce the volume of BM irradiated in gynecologic patients receiving intensity-modulated whole-pelvic radiation therapy (IM-WPRT). MATERIALS AND METHODS: A planning CT scan was obtained of a patient with early stage endometrial cancer. The same patient also underwent a Tc-99m sulfur colloid SPECT scan of the pelvis. Tc-99m sulfur colloid is sequestered by the macrophages in the BM thereby identifying areas of active (red) BM. Using image fusion software, the SPECT scan was aligned with the planning CT scan and used to delineate regions of active BM. An IMRT plan was then generated to provide coverage of the planning target volume (PTV) while sparing areas of active BM and other normal pelvic structures. RESULTS: The areas of high active BM density were observed predominantly in the lumbar vertebrae, sacrum and medial iliac crests. IMRT planning reduced the dose to these areas by 50% for doses greater than 30Gy compared to conventional planning. Furthermore, the IMRT plan did not compromise coverage of the PTV or sparing of normal tissues. CONCLUSIONS: Our results suggest that SPECT-BM imaging is a useful adjunct to IMRT planning in gynecologic patients undergoing IM-WPRT.

A Korean kindred with autosomal dominant nocturnal frontal lobe epilepsy and mental retardation.

BACKGROUND: A Korean family had distinctive clinical and neuroimaging features and carried the same genetic mutation that was found in a previously described Japanese kindred with autosomal dominant nocturnal frontal lobe epilepsy. OBJECTIVE: To describe the first Korean family with autosomal dominant nocturnal frontal lobe epilepsy. METHODS: Members of a large family, including 9 affected individuals from 3 generations, underwent a comprehensive genetic, clinical, electroencephalographic, neuropsychological, and neuroimaging evaluation. Affected members were tested for possible mutations in transmembrane regions 1 through 3 of the neuronal nicotinic acetylcholine receptor alpha4 subunit (CHRNA4) by direct sequencing and subsequent restriction analysis. RESULTS: Seizures began in childhood, presenting as nocturnal episodes of staring, confusion, shouting, perioral movements, unintelligible speech, and hand waving. Some patients had ictal or interictal epileptiform activity in the temporal and/or frontocentral areas. Neurological examination and brain magnetic resonance imaging results showed no abnormalities, except that all patients available for testing had mild to moderate mental retardation. Fluorodeoxyglucose F 18 with positron emission tomography showed mild decreased glucose uptake in the superior and middle frontal regions, more so on the left than on the right. Patient response to carbamazepine was poor. All affected members were heterozygous for the CHRNA4 Ser252Leu mutation. CONCLUSIONS: Disorders associated with mutations in the transmembrane region 2 of CHRNA4 are genetically and phenotypically heterogeneous. Distinctive features of this kindred include (1) mental retardation in all affected members available for testing, (2) abnormal brain findings on fluorodeoxyglucose F 18 with positron emission tomography, (3) poor response to carbamazepine, and (4) full penetrance.

Image processing tools for alpha-particle track-etch dosimetry.

In cases where both the source and cell geometry are well known, track-etch dosimetry allows the potential for individual cell dosimetry. However, analysis of track-etch images is both tedious and time-consuming. We describe here several image processing tools that we are using in conjunction with a track-etch based irradiator. Briefly, cells grown on LR 115 (a track-etch material) are irradiated from below by a collimated, planar alpha-particle source. Prior to irradiation, images of the cells are obtained. A computer program reads each image and automatically determines the location of individual cells. Next, the algorithm automatically identifies the cellular and nuclear boundaries. Following irradiation, and after the cells have reached their biological endpoint (e.g., cell survival), the cell dish is etched and images are obtained of alpha-particle tracks. Using the characteristic background pattern in the LR 115, the etched images are spatially registered to the original images. These two sets of images are then superimposed to create a composite image of the cells and associated alpha-particle tracks. Incorporating this tool into our irradiation scheme will enable more efficient analysis of the large amounts of data that are essential in assessing biological endpoints.

Characterization of an alpha-particle irradiator for individual cell dosimetry measurements.

A computer-controlled, alpha-particle irradiator is described that allows for the measurement of the number and location of alpha-particle hits to individual cell nuclei, and subsequent scoring of cell survival. Cells are grown on a track-etch material (LR 115) and images are obtained of the cells prior to irradiation. The cells are then irradiated from below by a planar, collimated Am-241 source. The exposure time is varied so that the average number of hits to cell nuclei ranges from 0 to 3. After cell survival has been scored, images of the etched material are obtained and spatially registered to the original cell images. The etched images and cellular images are superimposed allowing for the determination of the number and position of hits to individual cell nuclei. This paper characterizes the irradiator including the energy and fluence of the incident alpha particles. Additionally, we describe the sources of uncertainty associated with this experiment, including the cell dish repositioning and cell migration during scanning and irradiation.

Binary methods for the microdosimetric analysis of cell survival data from alpha-particle irradiation.

A new type of alpha-particle irradiator allows survival of each cell to be observed individually along with the size and shape of its nucleus and the positions of the hits it receives. This paper discusses methods of data analysis that can utilize these additional data. Using idealizations of the cell nucleus geometry (i.e., spheres, ellipsoids), the path length (l), energy deposited (e), and specific energy (z) has been determined on a cell-by-cell basis for 772 cells all subjected to the same fluence. Each cell is regarded as a Bernoulli trial with a different probability for success (colony formation). For the survival expectation, A exp(-z/z(o)), the values of A and z(o) are chosen to maximize the likelihood for the observed outcome. Similar results are presented using the alternate functional forms A exp(-e/e(o)) and A exp(-l/l(o)). With these parameter values, the goodness of fit is also evaluated using a chi-square method with variances given by the binary (Bernoulli) methods. A further purpose of the paper is to assess the validity of the microdosimetric computations that would have had to be made if these individual cell-by-cell experimental measurements were not available or were incomplete.

Imaging of ischemic heart disease.

Despite advances in the understanding and treatment of ischemic cardiomyopathy, characterized by extensive coronary artery disease and left ventricular (LV) dysfunction, the prognosis remains poor with only a 50-60% 5-year survival rate. The composition of atherosclerotic lesions is currently regarded as being more important than the degree of stenosis in determining acute events. If imaging techniques could distinguish vulnerable from stable plaques, then high-risk patient subgroups could be identified. Another important concept is that LV dysfunction may be the result of either scarring due to necrosis or to the presence of myocardial hibernation, in which there is sufficient blood flow to sustain viable myocytes, but insufficient to maintain systolic contraction. This concept of myocardial viability is critical for making optimal clinical management decisions. This review describes how noninvasive imaging methods can be used to distinguish regions of irreversibly injured myocardium from viable but hibernating segments. Technical advances in CT and MR have made imaging of the beating heart possible. Considerable clinical progress has already been made and further cardiac applications are expected. Radiologists therefore have new opportunities for involvement in cardiac imaging but must recognize the political implications as well as the diagnostic potential of these modalities not only for the heart, but also for the whole vascular system. This review focuses on imaging myocardial injury. It compares state-of-the-art CT and MR with more established yet contemporary echocardiography and nuclear scintigraphy.