Sarah Heard

Use of 111-Indium-labelled autologous eosinophils to establish the in vivo kinetics of human eosinophils in healthy subjects

Eosinophils are the major cellular effectors of allergic inflammation and represent an important therapeutic target. Although the genesis and activation of eosinophils have been extensively explored, little is known about their intravascular kinetics or physiological fate. This study was designed to determine the intravascular life span of eosinophils, their partitioning between circulating and marginated pools, and sites of disposal in healthy persons. Using autologous, minimally manipulated 111-Indium-labeled leukocytes with blood sampling, we measured the eosinophil intravascular residence time as 25.2 hours (compared with 10.3 hours for neutrophils) and demonstrated a substantial marginated eosinophil pool. γ camera imaging studies using purified eosinophils demonstrated initial retention in the lungs, with early redistribution to the liver and spleen, and evidence of recirculation from a hepatic pool. This work provides the first in vivo measurements of eosinophil kinetics in healthy volunteers and shows that 111-Indium-labeled eosinophils can be used to monitor the fate of eosinophils noninvasively.

Measurement of eosinophil kinetics in healthy volunteers.

Radiolabelled leukocyte scans are widely used in nuclear medicine to locate sites of infection and inflammation. Radiolabelling of leukocyte subpopulations can also yield valuable information on cell trafficking and kinetics in vivo, but care must be taken to minimize inadvertent cell activation ex vivo. Here, we describe the use of autologous indium(111)-labelled eosinophils to measure eosinophil intravascular life-span and monitor their distribution and fate using gamma camera imaging in healthy non-atopic individuals.

Optimization of PET/CT image quality using the GE ‘Sharp IR’ point-spread function reconstruction algorithm

Objective The objective of this study was to quantify any improvement with the GE ‘Sharp IR’ point-spread function (PSF) reconstruction algorithm in addition to ordered subsets expectation maximum (OSEM) and time-of-flight (TOF) reconstruction algorithms and establish the optimum parameters to be used in clinical studies. Materials and methods We conducted a range of experiments using the National Electrical Manufacturers Association image quality phantom filled with a 4 : 1 signal-to-background ratio. We scanned the phantom using the GE Discovery 690 PET/CT scanner. We varied iteration number and Gaussian filtration. Results were compared for OSEM, OSEM+TOF and OSEM+TOF+PSF reconstructions. A sample of 15 whole-body fluorine-18-fluorodeoxyglucose were reconstructed with OSEM+TOF and OSEM+TOF+PSF using a selection of optimum reconstruction parameters determined in phantom studies. Clinicians qualitatively ranked their preferred images to choose optimum parameters. Results The addition of PSF improved signal-to-noise ratios (SNRs), contrast, hot contrast recovery coefficients and noise over OSEM and OSEM+TOF reconstruction algorithms. SNRs were the highest at two iterations and with 0 or 2 mm filters with OSEM+TOF+PSF reconstruction in all phantom studies. Clinicians generally favoured OSEM+TOF+PSF reconstruction with three iterations and a 2 mm filter. Conclusion PSF reconstruction significantly improved image quality for both clinical and phantom studies. We recommended the optimum reconstruction parameters using three iterations, 24 subsets and a 2 mm filter, which improved SNRs by up to 28.8% for small lesions (P<0.05).

Use of Radiolabelled Leukocytes for Drug Evaluation in Man

The endeavour to radiolabel or simply “label” autologous leukocytes has been a major clinical need. The endeavour to improve the labelling conditions and minimise interventional stresses and maintain cell functionality has been the driving objective. This chapter focuses on novel techniques used in this laboratory to radiolabel leukocytes, examples of the clinical indications that such labelled products might be informative, and how we can use these labelled cells in clinical situations to describe the life cycle behaviour (transit times and migratory capacity) of these labelled cells. Labelling techniques which preserve leukocyte functionality will assist in the development of new anti-inflammatory agents, anti-infectives, and indeed any drug or biologic where their clinical use may have an effect on these cells. Examples of labelling methods and clinical scenarios with imaging are described for conditions such as abscesses, ARDS, COPD, rheumatoid arthritis, inflammatory bowel disease, and vasculitis.

Circulating granulocyte lifespan in compensated alcohol-related cirrhosis: a pilot study

Although granulocyte dysfunction is known to occur in cirrhosis, in vivo studies of granulocyte lifespan have not previously been performed. The normal circulating granulocyte survival half‐time (G − t½), determined using indium‐111 (111In)‐radiolabeled granulocytes, is ~7 h. In this pilot study, we aimed to measure the in vivo G − t½ in compensated alcohol‐related cirrhosis. Sequential venous blood samples were obtained in abstinent subjects with alcohol‐related cirrhosis over 24 h post injection (PI) of minimally manipulated 111In‐radiolabeled autologous mixed leukocytes. Purified granulocytes were isolated from each sample using a magnetic microbead‐antibody technique positively selecting for the marker CD15. Granulocyte‐associated radioactivity was expressed relative to peak activity, plotted over time, and G − t½ estimated from data up to 12 h PI. This was compared with normal neutrophil half‐time (N − t½), determined using a similar method specifically selecting neutrophils in healthy controls at a collaborating center. Seven patients with cirrhosis (six male, aged 57.8 ± 9.4 years, all Child‐Pugh class A) and seven normal controls (three male, 64.4 ± 5.6 years) were studied. Peripheral blood neutrophil counts were similar in both groups (4.6 (3.5 − 5.5) × 109/L vs. 2.8 (2.7 − 4.4) × 109/L, respectively, P = 0.277). G − t½ in cirrhosis was significantly lower than N − t½ in controls (2.7 ± 0.5 h vs. 4.4 ± 1.0 h, P = 0.007). Transient rises in granulocyte and neutrophil‐associated activities occurred in four patients from each group, typically earlier in cirrhosis (4–6 h PI) than in controls (8–10 h), suggesting recirculation of radiolabeled cells released from an unidentified focus. Reduced in vivo granulocyte survival in compensated alcohol‐related cirrhosis is a novel finding and potentially another mechanism for immune dysfunction in chronic liver disease. Larger studies are needed to corroborate these pilot data and assess intravascular neutrophil residency in other disease etiologies.

Successful treatment of residual pituitary adenoma in persistent acromegaly following localisation by 11C-methionine PET co-registered with MRI

OBJECTIVE To determine if functional imaging using 11C-methionine positron emission tomography co-registered with 3D gradient echo MRI (Met-PET/MRI), can identify sites of residual active tumour in treated acromegaly, and discriminate these from post-treatment change, to allow further targeted treatment. DESIGN/METHODS Twenty-six patients with persistent acromegaly after previous treatment, in whom MRI appearances were considered indeterminate, were referred to our centre for further evaluation over a 4.5-year period. Met-PET/MRI was performed in each case, and findings were used to decide regarding adjunctive therapy. Four patients with clinical and biochemical remission after transsphenoidal surgery (TSS), but in whom residual tumour was suspected on post-operative MRI, were also studied. RESULTS Met-PET/MRI demonstrated tracer uptake only within the normal gland in the four patients who had achieved complete remission after primary surgery. In contrast, in 26 patients with active acromegaly, Met-PET/MRI localised sites of abnormal tracer uptake in all but one case. Based on these findings, fourteen subjects underwent endoscopic TSS, leading to a marked improvement in (n = 7), or complete resolution of (n = 7), residual acromegaly. One patient received stereotactic radiosurgery and two patients with cavernous sinus invasion were treated with image-guided fractionated radiotherapy, with good disease control. Three subjects await further intervention. Five patients chose to receive adjunctive medical therapy. Only one patient developed additional pituitary deficits after Met-PET/MRI-guided TSS. CONCLUSIONS In patients with persistent acromegaly after primary therapy, Met-PET/MRI can help identify the site(s) of residual pituitary adenoma when MRI appearances are inconclusive and direct further targeted intervention (surgery or radiotherapy).