Radionuclide-labeled red blood cells: current status and future prospects

Preclinical PET Imaging and Toxicity Study of a 68Ga-Functionalized Polymeric Cardiac Blood Pool Agent

Cardiac blood pool imaging is currently performed almost exclusively with 99mTc-based compounds and SPECT/CT imaging. Using a generator-based PET radioisotope has a few advantages, including not needing nuclear reactors to produce it, obtaining better resolution in humans, and potentially reducing the radiation dose to the patient. When the shortlived radioisotope 68Ga is used, it can be applied repeatedly on the same day—for example, for the detection of bleeding. Our objective was to prepare and evaluate a long-circulating polymer functionalized with gallium for its biodistribution, toxicity, and dosimetric properties. A 500 kDa hyperbranched polyglycerol was conjugated to the chelator NOTA and radiolabeled rapidly at room temperature with 68Ga. It was then injected intravenously into a rat, and gated imaging allowed us to easily observe wall motion and cardiac contractility, confirming the suitability of this radiopharmaceutical for cardiac blood pool imaging. Internal radiation dose calculations showed that the radiation doses that patients would receive from the PET agent would be 2.5× lower than those from the 99mTc agent. A complete 14-day toxicology study in rats concluded that there were no gross pathology findings, changes in body or organ weights, or histopathological events. This radioactive-metal-functionalized polymer might be a suitable non-toxic agent to advance for clinical application.

Magnetic particle imaging: tracer development and the biomedical applications of a radiation-free, sensitive, and quantitative imaging modality

Magnetic particle imaging (MPI) is an emerging tracer-based modality that enables real-time three-dimensional imaging of the non-linear magnetisation produced by superparamagnetic iron oxide nanoparticles (SPIONs), in the presence of an external oscillating magnetic field. As a technique, it produces highly sensitive radiation-free tomographic images with absolute quantitation. Coupled with a high contrast, as well as zero signal attenuation at-depth, there are essentially no limitations to where that can be imaged within the body. These characteristics enable various biomedical applications of clinical interest. In the opening sections of this review, the principles of image generation are introduced, along with a detailed comparison of the fundamental properties of this technique with other common imaging modalities. The main feature is a presentation on the up-to-date literature for the development of SPIONs tailored for improved imaging performance, and developments in the current and promising biomedical applications of this emerging technique, with a specific focus on theranostics, cell tracking and perfusion imaging. Finally, we will discuss recent progress in the clinical translation of MPI. As signal detection in MPI is almost entirely dependent on the properties of the SPION employed, this work emphasises the importance of tailoring the synthetic process to produce SPIONs demonstrating specific properties and how this impacts imaging in particular applications and MPI's overall performance.

M. de Rosales R. Radiolabelling of Extracellular Vesicles for PET and SPECT imaging

Extracellular vesicles (EVs) such as exosomes and microvesicles have gained recent attention as potential biomarkers of disease as well as nanomedicinal tools, but their behaviour in vivo remains mostly unexplored. In order to gain knowledge of their in vivo biodistribution it is important to develop imaging tools that allow us to track EVs over time and at the whole-body level. Radionuclide-based imaging (PET and SPECT) have properties that allow us to do so efficiently, mostly due to their high sensitivity, imaging signal tissue penetration, and accurate quantification. Furthermore, they can be easily translated from animals to humans. In this review, we summarise and discuss the different studies that have used PET or SPECT to study the behaviour of EVs in vivo. With a focus on the different radiolabelling methods used, we also discuss the advantages and disadvantages of each one, and the challenges of imaging EVs due to their variable stability and heterogeneity.

Differentiation of insulinoma from accessory spleen by 99mTc-labelled heat-denaturated red blood cell scintigraphy: case report

BACKGROUND

Neuroendocrine tumors (NETs) are rare tumors harboring overexpression of somatostatin receptors (SSTRs) on their cell membrane. Because some organs, such as the spleen, adrenal glands and liver, physiologically express SSTR, it might be challenging to distinguish some pancreatic NETs located in the pancreatic tail from the accessory spleen next to the splenic hilum. In this manuscript, we report a case with hypoglycemia attack and 2 different masses displayed by Gallium 68-tetraazacyclododecane tetraacetic acid-octreotate (⁶⁸Ga-DOTATATE) positron emission tomography/computed tomography (PET/CT).

CASE PRESENTATION

A 63-year-old woman presented to the hospital with confusion and profuse sweating. Biochemical diagnosis of insulinoma was established. ⁶⁸Ga-DOTATATE PET/CT revealed two masses with increased tracer uptake located adjacent to the splenic hilum and inferior pole of the spleen which were initially reported as two separate accessory spleens. Then, ^99mTc-labelled heat-denaturated red blood cell (^99mTc-HDRBC) scintigraphy-single-photon emission computed tomography (SPECT)/CT was performed to distinguish a NET in the pancreatic tail from accessory spleen at the splenic hilum. Enhanced tracer uptake remained in the inferior pole of spleen, but not in the splenic hilum. The lesions were suggestive of insulinoma in the pancreatic tail and an accessory spleen adjacent to the inferior pole of the spleen.

CONCLUSION

Approximately 10% of the population have an accessory spleen which can show similar imaging characteristics with pancreatic NETs, especially if located in the pancreatic tail. In our presented case, ^99mTc-HDRBC scintigraphy-SPECT/CT is a useful nuclear medicine method to differentiate a NET in the pancreatic tail from accessory spleen at the splenic hilum which may avoid unnecessary surgeries in the presence of enhanced tracer uptake or vice versa.

[Discontinuation of Chromium-51 for clinical use: What are the possible alternatives for radiopharmacies and nuclear medicine departments?]

OBJECTIVES

Last October, the nuclear medicine departments were informed of the closure of the chromium-51 production line for clinical use. This radionuclide has different diagnostic indications in nephrology and hematology. It was therefore essential to set up alternative exploration protocols to overcome this production stoppage.

METHODS

Chromium-51 EDTA has been replaced by technetium-99m DTPA for the determination of glomerular filtration rates. Sodium chromate was substituted by sodium pertechnetate for the determination of globular volumes. A retrospective analysis of the chromium-51 data was performed followed by a prospective study, from January to December 2019 for technetium tracers.

RESULTS

One hundred and forty-four patients were included in the study. Forty-two EDTA-⁵¹Cr and 30 DTPA-^99mTc exams were conducted and compared. There were no significant differences between the methods used to assess renal function (P=0.355). For the determination of blood cell and plasma volumes, 47 tests with ⁵¹Cr and ¹²⁵I and 25 tests with ^99mTc and ¹²⁵I were performed and compared. There were no significant differences in the determination of total (P=0.325) and globular (P=0.148) volumes.

CONCLUSIONS

The study carried out shows that there is no significant difference between the results obtained with chromium-51 and technetium tracers. As a result, clinical activity was maintained in good conditions.

On-cartridge preparation and evaluation of 68Ga-, 89Zr- and 64Cu-precursors for cell radiolabelling

INTRODUCTION

Indium-111 when formulated as indium-111 oxine remains the gold standard for long term cell tracking, whereas radiometals for improved PET applications still have to be established. We here describe the on-cartridge formation of gallium-68, zirconium-89 and copper-64 complexes in small volumes suitable for cell labelling, including labelling of red blood cells (RBC) and white blood cells (WBC) and their biological evaluation in vivo.

METHODS

Small volumes (1-2 mL) of tracers (oxine, tropolone) were directly prepared on an anion exchange cartridge (Sep-Pak QMA). Cells were radiolabelled and the labelling efficiency and efflux were evaluated. The in vivo biodistribution of copper-64-labelled WBC using [⁶⁴Cu][Cu(oxinate)₂] and [⁶⁴Cu][Cu(tropolonate)₂] was monitored in an infection and inflammation animal model using BALB/c mice.

RESULTS

On-cartridge concentration of gallium-68, zirconium-89 and copper-64 enabled formation of oxine and tropolone tracers in small volumes with good yields (≥50%) and quality (extraction ≥90%). Prepared tracers radiolabelled the RBC comparable to indium-111 tracers and in vivo biodistribution of copper-64 labelled WBC showed clear accumulation of cells at the site of infection and inflammation.

CONCLUSIONS

This on-cartridge preparation method enables simple formation of various PET tracers for cell radiolabelling. Zirconium-89 and copper-64 tracers radiolabelled cells with sufficient stability. Due to their longer half-life this approach could be promising for routine applications where longer evaluation periods for cell tracking are needed.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

This novel approach for on-cartridge concentration and preparation of oxine and tropolone precursors with different positron emitters, in small volume and suitable pH, offers a versatile tool towards cell labelling for preclinical and clinical PET applications.

A perspective on a rapid and radiation-free tracer imaging modality, magnetic particle imaging, with promise for clinical translation

Magnetic particle imaging (MPI), introduced at the beginning of the twenty-first century, is emerging as a promising diagnostic tool in addition to the current repertoire of medical imaging modalities. Using superparamagnetic iron oxide nanoparticles (SPIOs), that are available for clinical use, MPI produces high contrast and highly sensitive tomographic images with absolute quantitation, no tissue attenuation at-depth, and there are no view limitations. The MPI signal is governed by the Brownian and Néel relaxation behavior of the particles. The relaxation time constants of these particles can be utilized to map information relating to the local microenvironment, such as viscosity and temperature. Proof-of-concept pre-clinical studies have shown favourable applications of MPI for better understanding the pathophysiology associated with vascular defects, tracking cell-based therapies and nanotheranostics. Functional imaging techniques using MPI will be useful for studying the pathology related to viscosity changes such as in vascular plaques and in determining cell viability of superparamagnetic iron oxide nanoparticle labeled cells. In this review article, an overview of MPI is provided with discussions mainly focusing on MPI tracers, applications of translational capabilities ranging from diagnostics to theranostics and finally outline a promising path towards clinical translation.

Automated synthesis of [68Ga]oxine, improved preparation of 68Ga-labeled erythrocytes for blood-pool imaging, and preclinical evaluation in rodents

Radiolabeled erythrocytes have multiple applications in nuclear medicine, including blood pool imaging. Historically they have been labeled with SPECT radionuclides. A PET blood pool imaging agent is highly desirable as it would improve clinical applications with better image quality and resolution, higher sensitivity, and dynamic scanning capabilities. With the coming of age of modern 68Ge/68Ga generator systems, gallium-68 is now widely accessible. In this paper we describe an updated method for the preparation of 68Ga-labeled erythrocytes and their preliminary use in rodent blood pool imaging. A novel automated synthesis of [68Ga]oxine using a 68Ga/68Ge generator and automated synthesis module is reported. [68Ga]Oxine was synthesized in 50 ± 5% (n = 3) non-decay corrected radiochemical yield and >99% radiochemical purity. Rat and human erythrocytes were successfully labeled with the complex in 42% RCY, and the 68Ga-labeled erythrocytes have been shown to clearly image the blood pool in a healthy rat. Human erythrocytes labelled with [68Ga]oxine were shown to be viable up to 2 hours post-labelling, and washout of the radiolabel was minimal up to 1 hour post-labelling. Further optimization of the labeling method to translate for use in human cardiac and oncologic blood pool PET imaging studies, is underway.

Preincubation with Sn-complexes causes intensive intracellular retention of 99mTc in thyroid cells in vitro

Technetium radiopharmaceuticals are well established in nuclear medicine. Besides its well-known gamma radiation, 99mTc emits an average of five Auger and internal conversion electrons per decay. The biological toxicity of these low-energy, high-LET (linear energy transfer) emissions is a controversial subject. One aim of this study was to estimate in a cell model how much 99mTc can be present in exposed cells and which radiobiological effects could be estimated in 99mTc-overloaded cells. Methods: Sodium iodine symporter (NIS)- positive thyroid cells were used. 99mTc-uptake studies were performed after preincubation with a non-radioactive (cold) stannous pyro - phosphate kit solution or as a standard 99mTc pyrophosphate kit preparation or with pure pertechnetate solution. Survival curves were analyzed from colony-forming assays. Results: Preincubation with stannous complexes causes irreversible intracellular radioactivity retention of 99mTc and is followed by further pertechnetate influx to an unexpectedly high 99mTc level. The uptake of 99mTc pertechnetate in NIS-positive cells can be modified using stannous pyrophosphate from 3–5% to >80%. The maximum possible cellular uptake of 99mTc was 90 Bq/cell. Compared with nearly pure extracellular irradiation from routine 99mTc complexes, cell survival was reduced by 3–4 orders of magnitude after preincubation with stannous pyrophosphate. Conclusions: Intra cellular 99mTc retention is related to reduced survival, which is most likely mediated by the emission of low-energy electrons. Our findings show that the described experiments constitute a simple and useful in vitro model for radiobiological investigations in a cell model.

Magnetic Particle Imaging for Highly Sensitive, Quantitative, and Safe in Vivo Gut Bleed Detection in a Murine Model

Gastrointestinal (GI) bleeding causes more than 300 000 hospitalizations per year in the United States. Imaging plays a crucial role in accurately locating the source of the bleed for timely intervention. Magnetic particle imaging (MPI) is an emerging clinically translatable imaging modality that images superparamagnetic iron-oxide (SPIO) tracers with extraordinary contrast and sensitivity. This linearly quantitative modality has zero background tissue signal and zero signal depth attenuation. MPI is also safe: there is zero ionizing radiation exposure to the patient and clinically approved tracers can be used with MPI. In this study, we demonstrate the use of MPI along with long-circulating, PEG-stabilized SPIOs for rapid in vivo detection and quantification of GI bleed. A mouse model genetically predisposed to GI polyp development (ApcMin/+) was used for this study, and heparin was used as an anticoagulant to induce acute GI bleeding. We then injected MPI-tailored, long-circulating SPIOs through the tail vein, and tracked the tracer biodistribution over time using our custom-built high resolution field-free line (FFL) MPI scanner. Dynamic MPI projection images captured tracer accumulation in the lower GI tract with excellent contrast. Quantitative analysis of the MPI images show that the mice experienced GI bleed rates between 1 and 5 μL/min. Although there are currently no human scale MPI systems, and MPI-tailored SPIOs need to undergo further development and evaluation, clinical translation of the technique is achievable. The robust contrast, sensitivity, safety, ability to image anywhere in the body, along with long-circulating SPIOs lends MPI outstanding promise as a clinical diagnostic tool for GI bleeding.

Converting Red Blood Cells to Efficient Microreactors for Blood Detoxification

A simple method to convert red blood cells (RBCs) into efficient microreactors is reported. Triton X-100 is employed at finely tuned concentrations to render RBCs highly permeable to substrates, while low concentrations of glutaraldehyde are used to stabilize cells. The ability for blood detoxification of these microreactors is demonstrated.

Splenic scintigraphy for further differentiation of unclear (68) Ga-DOTATOC-PET/CT findings: Strengths and limitations

Splenic scintigraphy has been described to be a powerful tool in unclear (68 ) Ga-DOTATOC-PET/CT findings, allowing differentiation between somatostatin receptor (Sst)-positive tissue deriving from neuroendocrine tumour (NET) and functioning splenic tissue. However, our own experiences sometimes show a lack of identification on splenic scintigraphy, especially in small lesions, leading to uncertainties regarding the safe identification of NET or splenic tissue. Here, we report on 10 cases with (68) Ga-DOTATOC-PET/CT and (99m) Tc-heat-denaturated red blood cell (HDRBC) scintigraphy and we illustrate the strengths and limitations of (99m) Tc-HDRBC scintigraphy in this context.

In vivo MRI cell tracking using perfluorocarbon probes and fluorine-19 detection

This article presents a brief review of preclinical in vivo cell-tracking methods and applications using perfluorocarbon (PFC) probes and fluorine-19 ((19) F) MRI detection. Detection of the (19) F signal offers high cell specificity and quantification ability in spin density-weighted MR images. We discuss the compositions of matter, methods and applications of PFC-based cell tracking using ex vivo and in situ PFC labeling in preclinical studies of inflammation and cellular therapeutics. We also address the potential applicability of (19) F cell tracking to clinical trials.

Effects of anti-VEGF on predicted antibody biodistribution: roles of vascular volume, interstitial volume, and blood flow

Background

The identification of clinically meaningful and predictive models of disposition kinetics for cancer therapeutics is an ongoing pursuit in drug development. In particular, the growing interest in preclinical evaluation of anti-angiogenic agents alone or in combination with other drugs requires a complete understanding of the associated physiological consequences.

Methodology/Principal Findings

Technescan™ PYP™, a clinically utilized radiopharmaceutical, was used to measure tissue vascular volumes in beige nude mice that were naïve or administered a single intravenous bolus dose of a murine anti-vascular endothelial growth factor (anti-VEGF) antibody (10 mg/kg) 24 h prior to assay. Anti-VEGF had no significant effect (p>0.05) on the fractional vascular volumes of any tissues studied; these findings were further supported by single photon emission computed tomographic imaging. In addition, apart from a borderline significant increase (p = 0.048) in mean hepatic blood flow, no significant anti-VEGF-induced differences were observed (p>0.05) in two additional physiological parameters, interstitial fluid volume and the organ blood flow rate, measured using indium-111-pentetate and rubidium-86 chloride, respectively. Areas under the concentration-time curves generated by a physiologically-based pharmacokinetic model changed substantially (>25%) in several tissues when model parameters describing compartmental volumes and blood flow rates were switched from literature to our experimentally derived values. However, negligible changes in predicted tissue exposure were observed when comparing simulations based on parameters measured in naïve versus anti-VEGF-administered mice.

Conclusions/Significance

These observations may foster an enhanced understanding of anti-VEGF effects in murine tissues and, in particular, may be useful in modeling antibody uptake alone or in combination with anti-VEGF.

Imaging of gastrointestinal bleeding

Radiological techniques are important in evaluating patients with gastrointestinal bleeding. Scintigraphic, computed tomographic angiographic, and enterographic techniques are sensitive tools in identifying the source of bleeding and may be useful in identifying patients likely to have a benign course and in selecting patients for therapeutic intervention. Angiography plays a key role in bleeding localization, and modern embolization techniques make this a viable therapeutic option. With the refining developments in body imaging and related reconstructive techniques, it is likely that radiological interventions will play an expanding and critical role in evaluating patients with gastrointestinal hemorrhage in the future.

Development and evaluation of a novel method for preclinical measurement of tissue vascular volume

Identification of clinically predictive models of disposition kinetics for antibody therapeutics is an ongoing pursuit in drug development. To encourage translation of drug candidates from early research to clinical trials, clinical diagnostic agents may be used to characterize antibody disposition in physiologically relevant preclinical models. TechneScan PYP was employed to measure tissue vascular volumes (V(v)) in healthy mice. Two methods of red blood cell (RBC) labeling were compared: a direct in vivo method that is analogous to a clinical blood pool imaging protocol, and an indirect method in which radiolabeled blood was transfused from donor mice into recipient mice. The indirect method gave higher precision in RBC labeling yields, lower V(v) values in most tissues, and lower (99m)Tc uptake in kidneys and bladder by single photon emission computed tomographic (SPECT) imaging relative to the direct method. Furthermore, the relative influence of each method on the calculated area under the first 7 days of the concentration-time curve (AUC(0-7)) of an IgG in nude mice was assessed using a physiologically based pharmacokinetic model. The model was sensitive to the source of V(v) values, whether obtained from the literature or measured by either method, when used to predict experimental AUC(0-7) values for radiolabeled trastuzumab in healthy murine tissues. In summary, a novel indirect method for preclinical determination of V(v) offered higher precision in RBC labeling efficiency and lower renal uptake of (99m)Tc than the direct method. In addition, these observations emphasize the importance of obtaining accurate physiological parameter values for modeling antibody uptake.

Markedly low hemoglobin A1c in a patient with an unusual presentation of beta-thalassemia minor

OBJECTIVE

To describe very low hemoglobin A1c levels in a patient with type 2 diabetes mellitus and an unusual presentation of beta-thalassemia minor.

METHODS

We present the clinical and laboratory findings of the study patient.

RESULTS

A 64-year-old African American man with type 2 diabetes mellitus was referred to the endocrinology clinic with a hemoglobin A1c level of 1.6% despite elevated blood glucose concentrations. A red blood cell survival study with chromium-51 revealed that he had a reduced erythrocyte life span less than 25% of normal. He also had a markedly elevated reticulocyte count ranging from 236 to 534 x 10(3)/microL (reference range, 25-75 x 10(3)/microL). The laboratory findings, which are not characteristic of beta-thalassemia minor, could be the cause of the markedly low hemoglobin A1c in this patient.

CONCLUSIONS

Although rare, when associated with marked erythrocyte turnover, beta-thalassemia minor can lead to a severe reduction in HbA1c levels. In this scenario, glycemic control is best assessed by measuring fructosamine.

Effect of terlipressin on blood volume distribution in patients with cirrhosis

BACKGROUND

Patients with cirrhosis and portal hypertension have an altered blood volume distribution and a hyperdynamic systemic circulation. Terlipressin is known to reduce portal pressure by decreasing splanchnic inflow, but its effect on the blood volume distribution is unknown. The aim of the study was to investigate changes in regional blood volume distribution and systemic haemodynamics after administration of terlipressin to patients with cirrhosis.

METHODS

Blood volume distribution was determined in 13 patients with cirrhosis and portal hypertension by a dual-head gamma-camera technique and systemic haemodynamics was measured before and after intravenous administration of terlipressin (2 mg).

RESULTS

Terlipressin increased the blood volume in the thorax region (+6.0%, P < 0.002) and the liver region (+12.2%, P < 0.002), whereas blood volume in the splanchnic region remained unchanged. Systemic vascular resistance (SVR) and mean arterial blood pressure increased after terlipressin (+34 and +21%, P < 0.001). The increase in liver blood volume correlated directly with the increase in SVR (r = 0.88. P < 0.001).

CONCLUSIONS

Terlipressin ameliorates the hyperdynamic circulation, increases thorax and liver blood volumes, but produces no effect on the splanchnic blood volume. Besides decreasing the splanchnic inflow, terlipressin may affect portal pressure by causing vasodilatation of intrahepatic vessels.

Radiolabeled liposomes for scintigraphic imaging

Liposomes have been investigated extensively as carriers for drugs in attempts to achieve selective deposition and/or reduced toxicity. Liposomes radiolabeled with gamma emitters such as (67)Ga, (111)In and (99m)Tc, can be used for imaging purposes. Liposomes as formulated in the past, are rapidly taken up by cells of the mononuclear phagocyte system (MPS), primarily those located in liver and spleen. The recent development of long-circulating liposomes (LCLs), yielded liposomes that oppose recognition by the MPS. The development of these LCLs with enhanced circulatory half-lives has broadened the potential of liposomes to scintigraphically visualize pathologic processes in vivo. Liposomes have been proposed for tumor imaging, infection imaging and blood pool imaging. Strategies have been developed that allow rapid, easy and efficient labeling of preformed liposomes with (111)In and (99m)Tc. There is now a vast body of preclinical evidence showing that LCLs can be used to image a wide variety of tumors as well as inflammatory lesions. The first studies in patients show that radiolabeled liposomes can image tumor and inflammatory lesions with good sensitivity and good specificity. Here, the present status of liposome-based radiopharmaceuticals for scintigraphic application is reviewed.

Tc-99m sulfur colloid scintigraphy for detecting perigraft flow following endovascular aortic aneurysm repair: A feasibility study

PURPOSE

To determine if scintigraphy with Tc-99m sulfur colloid can be used to detect perigraft flow after stent-graft repair of abdominal aortic aneurysm (AAA).

METHODS

Twenty-three men and two women aged 56-84 years (mean 71 years) underwent endoluminal AAA repair as part of the EVT Phase II trial [EVT = Endovascular Technologies (Menlo Park, CA, USA)]. Aneurysm size averaged 5.4 cm (range 3-8 cm). Sixteen bifurcated, seven tube, and two aorto-uniiliac grafts were placed. Two days after stent-graft placement, patients underwent both contrast-enhanced computed tomography (CT), including delayed views, and Tc-99m sulfur colloid scintigraphy.

RESULTS

Perigraft flow was found in only one patient at completion of angiography. Four additional patients had perigraft flow, discovered during their postoperative follow-up CT. Four patients had leaks at an attachment site and one had retrograde branch flow. Tc-99m sulfur colloid scintigraphy failed to diagnose any of the five leaks prospectively. In two of these patients, however, some abnormal paraaortic activity was noted in retrospect.

CONCLUSION

Tc-99m sulfur colloid scintigraphy was unable to demonstrate endoleak with either rapid flow (attachment site leak) or slow filling (branch flow).

Approaches and agents for imaging the vascular system

Several classes of vascular imaging agents are described: (1) liposome-based blood cell mimetics; (2) plasma protein mimetics; (3) small molecules that bind to plasma proteins in the circulation. The characteristic features of the different agents are described and critically compared, including the advantages and potential pitfalls of each individual type.

Targeted imaging of infection

The prompt identification, localization and characterization of focal sites of infection in the patients with fever is a critical step in clinical management, particularly, when localizing symptoms are not present. Although the classic signs of inflammation are suitable to localize injury at superficial sites or in the extremities, inflammation of internal structures, such as in the brain, chest and abdomen, can be difficult to localize without additional diagnostic procedures. Tissue injury, regardless of cause or anatomical site, results in a complex series of physiologic changes that we recognize as the inflammatory response. The inflammatory response is characterized by a series of biochemical events in the insulted cells and surrounding structures that results in the three major pathophysiological components: increased tissue perfusion, increased vascular permeability, and leukocytic exudation. Exploitation of the early attributes of the inflammatory process are not sufficient for the routine detection of inflammation. Currently, reagents for targeting infection represent cellular or protein components involved in the inflammatory process. Such approaches have met with some success as these agents comprise integral parts of the complex phenomena known as inflammation. This same fact also limits their utility. Improved agents for targeting infection will likely be based on small molecules whose diffusion into the lesion is not hindered by molecular size constraints and which bind to molecular targets at the site of infection/inflammation. In general, the lower molecular weight should also lead to enhanced blood clearance, avoiding elevated blood pool activity which contributes to background. New agents should also obviate the need to handle blood, as this represents potential hazards to both patient and the medical personnel alike.

Inferior mesenteric varix demonstrated by 99mTc-red blood cell gastrointestinal bleeding study

Reported here is a case of an inferior mesenteric varix demonstrated by 99mTc-red blood cell (RBC) scintigraphy performed for gastrointestinal bleeding in a 47-year-old man. It was shaped like a question mark ranging from the left upper abdomen to the pelvis. This is the first report of scintigraphic recognition of an inferior mesenteric varix.

The effect of cyclosporine-A on labeling blood cells with radiopharmaceuticals

The effect of cyclosporine-A (CsA) on the labeling efficiencies of red blood cells with reduced 99mTcO4-; leukocytes and platelets with 111In oxine was studied. Blood was used from rats treated with CsA (30 mg/kg body weight) for 28 consecutive days and from control rats. For 99mTc labeling of RBCs, blood was obtained from individual rats and in vitro labeling technique was used. For leukocyte and platelet labeling, blood was pooled from 5 rats either treated with CsA or control. Leukocytes/platelets were labeled with 111In oxine using routine techniques. The labeling efficiency for 99mTc RBCs was 83.42 +/- 0.83% (CsA treated) and 84.85 +/- 0.62% (control); 111In-oxine leukocytes was 38.5 +/- 1.75% (CsA treated) and 42.5 +/- 3.53% (control); and for 111In-oxine platelets, it was 74.0 +/- 2.5% (CsA treated) and 78.0 +/- 1.41% (control). Comparison of the results indicate that there is no difference between the percent labeling efficiencies of 99mTc RBCs, 111In-oxine leukocytes, and 111In-oxine platelets for CsA-treated and control rats. Hence, CsA does not interfere with the labeling process of blood cells with radiopharmaceuticals.

Failure to label red blood cells adequately in daily practice using an in vivo method: methodological and clinical considerations

This study was conducted to evaluate the frequency and possible causes of poor red blood cell (RBC) labelling when performing equilibrium gated blood pool (GBP) radionuclide angiography at rest with an in vivo method. The influence of the mode of administration on tagging efficiency was studied by investigating the image quality in 160 patients referred for evaluation of left ventricular (LV) function prior to or after coronary angiography, while using a roughly standardized administration protocol. The patients were subclassified into four groups according to the way both molecules involved in the tagging procedure were administered. When poor image quality was found (in 9.4% of the patients), the labelling efficiency was quantified and the frequency of failed tagging in each group was calculated. A significant association was found between poor labelling and the use of a Teflon catheter or butterfly needle for the injection of the stannous agent. In another 737 patients, in order to avoid the problems observed in the first group, a strict administration protocol was applied to analyse the frequency of poor tagging and its possible causes. Suboptimal image quality was present in 88 patients (11.9%). Quantitatively confirmed poor tagging was present in 36 of the 88 (40.9%, or 4.9% of the whole group); the remaining 52 patients showed borderline normal labelling (> 80% bound fraction). Drug interference was studied by comparing the medications used by the 36 patients showing poor binding with those used by 44 control patients. A significant relationship was found between the use of heparin or chemotherapy and the tagging. The influence of several clinical factors on the labelling was also investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Procedure for red blood cell labelling with 99mTc-HMPAO. Methodology and quality control

We present here results on the labelling of red blood cells with 99mTc-HMPAO as an alternative method to the usual in vitro technique. Anticoagulant agents, the labelling medium with plasma, and the lapse of time between 99mTc-HMPAO preparation and labelling are the main factors which affect the efficiency of the procedure. A 93.9 +/- 2.3% labelling yield was obtained with freshly prepared 99mTc-HMPAO. In vitro (tracer elution of 4.3 +/- 1.2% at 60 mins) and in vivo (percentage of plasma activity at 60 mins, 7.8 +/- 2.8%) stability of the label, as well as image quality, qualify 99mTc-HMPAO labelled red blood cells as a suitable agent for clinical use.

Radioisotopic labels for blood cell survival studies: a review

The different methods of labeling blood cells, in particular erythrocytes and platelets, for survival studies are reviewed. Besides the technical information about these procedures, attention is also paid to the indications of blood cell survival studies, the effective dose equivalent involved and the interpretation of the resulting data. In the final section the possibilities created by dual-labeling procedures are discussed.

Dual radioisotopic study: a technique for the evaluation of vasculogenic impotence

Arterial and venous systems are the main points for the evaluation of vasculogenic impotence. To evaluate both of these systems in the same study we propose a dual radioisotopic study in which 99mtechnetium (99mTc) and 133xenon (133Xe) were used. The changes in 99mTc and 133Xe radioactivities administered intravenously and intracavernously, respectively, were monitored before and after intracavernous papaverine injection. These changes were determined as time activity curves, which were generated from the region of interest over the penis. A 99mTc penogram index derived from the 99mTc time activity curve was significantly different in the control and arteriogenic impotence groups (131.67 +/- 74.6 versus 62.94 +/- 51.6, p less than 0.01). A meaningful correlation between 99mTc penogram index results and duplex ultrasonographic findings were observed (r = 0.905). 133Xe penogram index, derived from the 133Xe washout curve was significantly different in the control and venogenic impotence groups (-25.65 +/- 24.9 versus -56.09 +/- 13.4, p less than 0.01). Also, a meaningful correlation was obtained between pharmacocavernosometry and 133Xe penogram index results of venogenic impotent patients (r = 0.86). These findings suggest that the dual radioisotopic study will be a useful technique in the evaluation of the entire vascular system of the penis, since it is a noninvasive method.

Myocardial infarction in childhood: clinical analysis of 17 cases and medium term follow up of survivors

Between 1979 and 1989 17 patients aged two months to 12 years with acute myocardial infarction of any cause (other than after cardiac surgery) were seen at a children's hospital. Eight died from three days to three years after diagnosis (overall mortality 47%). The nine survivors, now aged 2-17 years, have been followed for one to 10 years (mean follow up five years) after infarction. The commonest causes of myocardial infarction in this series were anomalous origin of left coronary artery from the pulmonary artery (six patients (35%] and Kawasaki disease (five patients (27%]. The main symptoms of acute myocardial infarction were dyspnoea, vomiting, and difficulty feeding. Diagnosis was made in all patients by electrocardiography and confirmed by echocardiography, cardiac catheterisation, or at operation. All survivors were symptom free with excellent exercise capacity. The left ventricular ejection fraction in survivors ranged from 21% to 66%, and only one child was on regular cardiac medications. There were no cases of late sudden death. Twenty four hour Holter monitoring performed on survivors was normal (seven) or showed minor abnormalities only (one), suggesting that serious arrhythmia is rare after paediatric myocardial infarction. Myocardial infarction in children had a high early mortality; however, the incidence of serious arrhythmia was low in the survivors, who had a good exercise tolerance even when the left ventricular ejection fraction was low.

The enzyme-inhibitor approach to cell-selective labelling. III. Sulphonamide inhibitors of carbonic anhydrase as carriers for red cell labelling

Selective radiolabelling of red blood cells via an enzyme-inhibitor approach represents a novel method in diagnostic nuclear medicine. Current problems in blood pool labelling could be overcome by using selective sulphonamide inhibitors as carriers. Red cell carbonic anhydrase is identified as an ideal target enzyme for such an approach. A brief review of the target enzyme is presented together with the screening of a series of synthesised sulphonamide inhibitors. p-Iodobenzenesulphonamide, 4-[(4-iodophenyl)thio]benzenesulphonamide and 5-(4-bromophenyl)sulphonyl]thiophene-2-sulphonamide were found to be particularly potent, reversible, lipophilic inhibitors of carbonic anhydrase, characteristics that warrant their further investigation as potential carriers. 4-Iodo-3-(iodoacetamido)benzenesulphonamide was a moderate inhibitor but caused relatively fast irreversible inactivation, making it a candidate for longer term studies.

The enzyme-inhibitor approach to cell-selective labelling--I. Sulphonamide inhibitors of carbonic anhydrase as carriers for red cell labelling: in vitro uptake of pIBS by human red blood cells

Red cell carbonic anhydrase is identified as an ideal target in an enzyme-inhibitor approach to radiolabel localisation. Current problems in blood pool labelling could be overcome by using selective sulphonamide inhibitors as carriers. p-Iodobenzenesulphonamide (pIBS) was selected as the choice reagent for red blood cell labelling. Rapid uptake of [125I]-pIBS was found in vitro, consistent with passive diffusion across the cell membrane. The intracellular binding could be attributed to interaction with two specific acceptor sites, with dissociation constants of 4.9 +/- 1.0 and 0.10 +/- 0.05 mumol dm-3, and maximum binding capacities of 166 +/- 5 and 19.9 +/- 1.0 mumol dm-3, respectively under the experimental conditions. These data correlate with the two major carbonic anhydrase isozymes; acceptor assignments were confirmed by gel chromatography of the red cell lysate.

The use of sports medicine techniques in evaluating the problem equine athlete

Discovering the cause of poor performance in racehorses can often represent a considerable challenge eluding the more common diagnostic techniques available at the racetrack. Application of sports medicine techniques to these problem cases can aid in the diagnosis of poor performance. Central to the development of this capability has been the use of highspeed treadmills, allowing the racehorse to be evaluated in the controlled laboratory setting, at exercise intensities equivalent to those of racing. Video and cinematographic gait analysis can be used in the diagnosis of subtle lameness conditions. Evaluating hoof balance at high speed has also become an important technique for both lameness diagnosis and prevention. Correcting hoof imbalance normalizes the applied stresses on joints, ligaments, and tendons. Abnormal upper airway function resulting in increased resistance to airflow is major cause of poor racing performance. Often this cause of upper airway dysfunction is difficult to evaluate at rest or after exercise. A definitive diagnosis can be made in these cases using treadmill endoscopy to visualize upper airway function during peak exercise. Lower airway function can also affect performance capability. Radiographic and scintigraphic imaging modalities can be used to evaluate both global and regional lung function in cases of suspected pneumonia, EIPH, COPD, or emphysema. Reduced metabolic fitness can be a primary cause of poor performance due to inherent differences in capability, pathologic changes in the major body systems involved in exercise, or inadequate training. Metabolic stress testing can be used to evaluate the level of fitness in these cases. Orthopedic imaging has also become a valuable diagnostic technique for evaluating musculoskeletal injuries. Scintigraphic evaluation of soft tissue and bone and CT scanning are used to localize the source of lameness and to grade the severity of various orthopedic conditions such as arthritis and stress-induced bone disease that are often difficult to categorize with conventional radiography.

A method for determination of normal or abnormal blood volume in patients subjected to radionuclide cardiography

The blood volume can be measured after labelling of red blood cells with technetium-99m. In addition, the blood volume and its standard error of estimate can be calculated from the subject's sex, height and deviation from desired weight. By comparing the measured blood volume with the estimated normal blood volume and using a statistical test, it can be decided whether a measured blood volume is normal or not. This method was applied to a group of 36 patients with heart diseases. Four of the patients had abnormal blood volumes. In the remaining 32 patients the measured blood volumes were equally distributed around the estimated mean normal values. The method described for determination of normal/abnormal blood volumes can be considered a by-product of routine radionuclide cardiography.

A new 99mTc-red blood cell labeling procedure for cardiac blood pool imaging: clinical results

The first clinical results of a new 99mTc-red blood cell labeling procedure avoiding cell centrifugation are presented. One ml heparinized blood samples were incubated with small amounts of a stannous kit. By titration studies, ideal quantities of sodium hypochlorite for oxidation of extracellular tin and of EDTA as stabilizer of the label were found. The Cl- concentration and pH of the labeled blood were acceptable, and EDTA increased labeling yield and stability determined in vitro by a few percent. The new procedure gave a slightly higher labeling yield than a current technique using centrifugation of cells. Labeling efficiency expressed as cell bound/total activity was 96.6% +/- 1.3% in healthy subjects and 95.5% +/- 2.2% in cardiac patients and remained high for 2 h after reinjection. The biological halflife of labeled cells following the new procedure was 11-12 h rendering it suitable for serial determinations of radionuclide cardiography.

An improved noninvasive method for measurement of cardiac output and evaluation of left-sided cardiac valve incompetence

A time-saving method was developed to label red blood cells in vitro with 99mTc while avoiding centrifugation. After tin incubation, extracellular tin was oxidized by sodium hypochlorite, and EDTA was added for stabilizing the complex prior to 99mTc incubation. Labeling yields were 95%, and in vivo decay showed a high stability with a mean biologic half-life of eleven hours. The first-passage radionuclide technique for determination of cardiac output using the above-mentioned tracer was evaluated by using the left ventricle as area-of-interest with individual background correction after complete mixing of the tracer. This technique showed a high level of agreement with invasive methods. By combining this method for measurement of the forward stroke volume with the multigated equilibrium principle for determination of the total left ventricular stroke volume using similar background corrections, an exact evaluation of regurgitation fractions was obtained. In patients with aortic and mitral valve disease the noninvasive radionuclide technique gave similar but probably more accurate results as compared with contrast aortography and ventriculography. The radionuclide technique may be suitable for monitoring and selecting patients for surgical treatment.

Modeling sickle cell vasoocclusion in the rat leg: quantification of trapped sickle cells and correlation with 31P metabolic and 1H magnetic resonance imaging changes

We have developed an animal model to elucidate the acute effects of perfusion abnormalities on muscle metabolism induced by different density-defined classes of erythrocytes isolated from sickle cell anemia patients. Technetium-99m (99mTc)-labeled, saline-washed normal (AA), homozygous sickle (SS), or high-density SS (SS4) erythrocytes were injected into the femoral artery of the rat and quantitative 99mTc imaging, 31P magnetic resonance spectroscopy by surface coil at 2 teslas, and 1H magnetic resonance imaging at 0.15 tesla were performed. Between 5 and 25 microliters of SS4 cells was trapped in the microcirculation of the thigh (or 1-6 x 10(7) cells per cubic centimeter of tissue). In contrast, fewer SS discocytes (SS2) or AA cells were trapped (an equivalent packed cell volume of less than 6.7 microliters and 0.3 microliters, respectively). After injection of SS4 cells an initial increase in inorganic phosphate was observed in the region of the thigh served by the femoral artery, intracellular pH decreased, and subsequently the proton relaxation time T1 reached a broad maximum at 18-28 hr. When T1 obtained at this time was plotted against the volume of cells trapped, an increase of T1 over the control value of 411 +/- 48 msec was found that was proportional to the number of cells trapped. We conclude that the densest SS cells are most effective at producing vasoocclusion. The extent of the change detected by 1H magnetic resonance imaging is dependent on the amount of cells trapped in the microcirculation and the magnitude of the initial increase of inorganic phosphate.

Risk of aortic aneurysm surgery as assessed by preoperative gated heart pool scan

Gated heart pool scan measuring left ventricular ejection fraction (LVEF) was performed preoperatively in 72 patients presenting for elective repair of abdominal aortic aneurysm. Patients with a positive cardiac history were more likely to have a LVEF of less than or equal to 45 per cent (P less than 0.001). The operative mortality rate was 4 per cent. Each of three patients who died had a LVEF less than or equal to 35 per cent and developed cardiac failure which led to renal failure. Five other patients developed cardiac failure manifested by acute pulmonary oedema during the early postoperative period. There was no statistically significant association between a positive cardiac history and the occurrence of postoperative cardiac failure or death. However, patients with a LVEF of less than or equal to 45 per cent were more likely to develop postoperative cardiac failure (P = 0.004) while patients with a LVEF of less than or equal to 35 per cent had a greater chance of dying (P less than 0.001). No patient died with a LVEF greater than 35 per cent. Preoperative evaluation of LVEF can select patients at high risk of cardiac death from repair of abdominal aortic aneurysm. Such patients could be followed conservatively if they remain asymptomatic and the aneurysm does not enlarge. If operation is considered mandatory, patients with a low LVEF should receive intensive perioperative monitoring with enhancement of ventricular performance.

Cardiac nuclear medicine

In this paper, the principal applications of nuclear medicine to studies of the heart are described. First, gated cardiac blood pool imaging is discussed, then thallium-201 myocardial imaging, myocardial infarct scintigraphy with 99mTc pyrophosphate, and evaluation of intracardiac shunts. In gated cardiac blood pool imaging, the patient's red blood cells are labeled with 99mTc. Images of the cardiac blood pool are then obtained in multiple projections and displayed in an endless-loop cine display. Quantitative indices of cardiac function are readily obtained, and a variety of functional images can be generated. Blood pool imaging may also be performed with use of a first-pass technique that yields similar information. Applications of blood pool imaging are discussed. The theory and techniques of planar and tomographic thallium-201 myocardial imaging are described, together with their application in the diagnosis of coronary artery disease. The prognostic value of thallium imaging is also examined. Myocardial infarct imaging with 99mTc pyrophosphate is described, and clinical indications are reviewed. Left-to-right cardiac shunts can be evaluated by following the first transit of a bolus of radiopharmaceutical through the lungs. Right-to-left shunts may be evaluated by injection of 99mTc macroaggregated albumin.

Quantitative radionuclide angiocardiography

Quantitation of cardiac pump function using radionuclide angiocardiography provides objective information for the management of patients with heart disease. Left and right ventricular ejection fraction, stroke volume ratio, ejection rate, diastolic function, ventricular volume, parametric imaging, amplitude and phase analysis, and shunt quantification can be measured from the radionuclide angiocardiogram at rest, during exercise, and during pharmacologic interventions. This review describes these methods and discusses their reliability and their role in the clinical assessment of patients with cardiac disease.

Differences in left ventricular function between anterior and inferior myocardial infarction of equivalent enzymatic size

The reasons for the poorer prognosis of anterior versus inferior myocardial infarction of equivalent enzymatic size remain uncertain. We investigated whether there are differences in left ventricular function between patients with anterior and inferior infarctions of equivalent enzymatic size to account for their differing outcomes. Clinical, serum enzyme, and electrocardiographic data were prospectively recorded in a consecutive series of patients less than 70 years of age with their first myocardial infarction. At 29 +/- 6 days following infarction, ejection fraction and left ventricular wall motion were assessed by gated heart scintigraphy and functional capacity by treadmill exercise testing in 19 patients with anterior and in 23 patients with inferior myocardial infarction. Peak creatine kinase and QRS scores were used to estimate total infarct size and left ventricular infarct size respectively. The anterior infarcts were of similar size to the inferior infarcts as determined by peak creatine kinase (1444 [mean] +/- 1161 [SD] U/L versus 1484 [mean] +/- 1182 [SD] U/L, respectively, P = 0.91) and peak aspartate transaminases (174 +/- 112 U/L versus 164 +/- 102 U/L, P = 0.78). The anterior myocardial infarct group had a greater percentage of the left ventricle infarcted on QRS scoring than the inferior infarct group (25.9 +/- 14.4% versus 11.1 +/- 6.0% respectively, P = 0.0004), lower global left ventricular ejection fraction (45.8 +/- 16% versus 54.6 +/- 9.2%, P = 0.04) and greater left ventricular regional wall abnormality. A significant negative correlation existed between left ventricular ejection fraction and peak creatine kinase for both groups, but was more marked with anterior infarction (r = -0.78, P less than 0.01) compared with inferior infarction (r = -0.49, P less than 0.05). Exercise-induced ST segment elevation was more frequent in the anterior than the inferior infarct group (59% versus 18%, P less than 0.02). However, both infarct locations had similar exercise tolerance, exercise-induced angina and ST segment depression. Despite equivalence of infarct size of the two infarct locations on enzyme testing, anterior infarction was associated with greater abnormality of left ventricular function with lower resting global left ventricular ejection fraction; greater resting left ventricular regional wall abnormality and greater exercise-induced ST segment elevation. These differences probably contribute to the poorer prognosis of patients with anterior infarction compared to those with inferior infarction of equivalent enzymatic size, given the previously well-documented prognostic importance of left ventricular function.

A simple in vitro method of radiolabelling human erythrocytes in whole blood with 113mIn-tropolonate

A simple and rapid in vitro procedure has been developed for selectively radiolabelling erythrocytes in whole blood using 113mIn-tropolonate. A maximum labelling efficiency of 97% was achieved, of which 95.5% was on the erythrocytes after only 5 min incubation of whole blood at room temperature. The optimum amount of tropolone for labelling whole blood was 10 micrograms of tropolone per ml of blood using acid-citrate dextrose (ACD) as the anticoagulant and 50 micrograms of tropolone per ml of blood using heparin. Under these optimum conditions, only 2.5% of the cell-bound 113mIn was released from the labelled cells during a 1 h in vitro incubation in cell-free plasma, irrespective of the anticoagulant used. These results suggest that 113mIn-tropolonate may prove to be a useful in vitro agent for labelling erythrocytes for short-term clinical investigations, especially at centres where 99mTc and 111In are unavailable.