18F-FDG PET/CT for the quantification of inflammation in large carotid artery plaques

Synthesis, radiolabeling, and biological evaluation of methyl 6-deoxy-6-[18F]fluoro-4-thio-α-d-maltotrioside as a positron emission tomography bacterial imaging agent

We developed fluorine-18 ([18F]) labeled methyl 6-deoxy-6-fluoro-4-thio-α-d-maltotrioside ([18F]MFTMT) for bacterial imaging and evaluated its stability and efficacy in vitro and in vivo. We found that Staphylococcus aureus (S. aureus) internalized [18F]MFTMT whereas Escherichia coli (E. coli) and CHO-K1 cells did not, in in vitro. Positron emission tomography imaging with [18F]MFTMT revealed that radioactivity accumulated not only in the S. aureus-infected group but also in the E. coli-infected and non-infectious inflammation groups. Further studies revealed that rat serum digested [18F]MFTMT into [18F]-methyl 6-deoxy-6-fluoro-4-thio-α-d-maltoside ([18F]MFTM), while [18F]MFTMT was stable in human serum for 210 min. [18F]MFTM was identified as the only radioactive metabolite in vivo. Similar to [18F]MFTMT, [18F]MFTM was internalized only by S. aureus. [18F]MFTM was identified as the only radioactive metabolite in vivo. We found that the sodium-glucose co-transporter 1 (SGLT1) is expressed in inflammatory tissue, and SGLT1 overexpressing cells showed increased retention of [18F]MFTMT and [18F]MFTM in vitro. Our study showed that the thio-glycosyl bond is stable against enzymatic digestion, and maltotetraose or a longer maltodextrin backbone is desirable for bacteria-specific imaging to avoid nonspecific uptake by SGLT1.

Pericarotid Fat as a Marker of Cerebrovascular Risk

Vascular inflammation is widely recognized as an important factor in the atherosclerotic process, particularly in terms of plaque development and progression. Conventional tests, such as measuring circulating inflammatory biomarkers, lack the precision to identify specific areas of vascular inflammation. In this context, noninvasive imaging modalities can detect perivascular fat changes, serving as a marker of vascular inflammation. This review aims to provide a comprehensive overview of the key concepts related to perivascular carotid fat and its pathophysiology. Additionally, we examine the existing literature on the association of pericarotid fat with features of plaque vulnerability and cerebrovascular events. Finally, we scrutinize the advantages and limitations of the noninvasive assessment of pericarotid fat.

Comparison of SUVA/V and SUVA-V for Evaluating Atherosclerotic Inflammation in 18F-FDG PET/CT

Purpose

This study aimed to compare the clinical significance of two parameters, division of standardized uptake value (SUV) of target arterial activity by background venous blood pool activity (SUVA/V) and subtraction of background venous blood pool activity from SUV of target arterial activity (SUVA-V) of carotid arteries with atherosclerotic plaques using 18F-fluorodeoxyglucose (FDG) positron emission tomography and computed tomography (PET/CT).

Methods

Patients aged 50 years or more who were diagnosed with carotid artery stenosis of 50% or more with carotid Doppler ultrasonography and had torso 18F-FDG PET/CT were enrolled retrospectively and classified patients who developed cerebrovascular events (CVEs) within 5 years after 18F-FDG PET/CT scan as the active group and patients who did not experience the CVE within 5 years as an inactive group. We calculated SUVA/V and SUVA-V using measurements of SUVmax of carotid arteries and mean SUV of superior vena cava (SVC).

Results

SUVA-V, SUVA-V_high, and SUVA-V_low were significantly higher in the active group than in the inactive group, but neither SUVA/V, SUVA/V_high, nor SUVA/V_low showed significant differences between the active and inactive groups. The difference in rank between groups of SUVA/V_high and SUVA/V_low was greater than the difference in rank between groups of SUVA-V_high and SUVA-V_low. The CVE incidence differed between SUVA/V_high and SUVA/V_low of high carotid FDG uptake, but the CVE incidence did not differ between SUVA-V_high and SUVA-V_low of high carotid FDG uptake.

Conclusion

SUVA-V may be a more rational solution than SUVA/V for evaluating atherosclerotic plaque inflammation on 18F-FDG PET/CT.

Development of a simple standardized scoring system for assessing large vessel vasculitis by 18F-FDG PET-CT and differentiation from atherosclerosis

PURPOSE

This study is to develop a structured approach to distinguishing large-artery vasculitis from atherosclerosis using 18-fluorodeoxyglucose positron emission tomography combined with low-dose computed tomography (FDG PET/CT).

METHODS

FDG PET/CT images of 60 patients were evaluated, 30 having biopsy-proven giant cell arteritis (GCA; the most common form of large-artery vasculitis), and 30 with severe atherosclerosis. Images were evaluated by 12 nuclear medicine physicians using 5 criteria: FDG uptake pattern (intensity, distribution, circularity), the degree of calcification, and co-localization of calcifications with FDG-uptake. Criteria that passed agreement, and reliability tests were subsequently analysed for accuracy using receiver operator curve (ROC) analyses. Criteria that showed discriminative ability were then combined in a multi-component scoring system. Both initial and final 'gestalt' conclusion were also reported by observers before and after detailed examination of the images.

RESULTS

Agreement and reliability analyses disqualified 3 of the 5 criteria, leaving only FDG uptake intensity compared to liver uptake and arterial wall calcification for potential use in a scoring system. ROC analysis showed an area under the curve (AUC) of 0.90 (95%CI 0.87-0.92) for FDG uptake intensity. Degree of calcification showed poor discriminative ability on its own (AUC of 0.62; 95%CI 0.58-0.66). When combining presence of calcification with FDG uptake intensity into a 6-tiered scoring system, the AUC remained similar at 0.91 (95%CI 0.88-0.93). After exclusion of cases with arterial prostheses, the AUC increased to 0.93 (95%CI 0.91-0.95). The accuracy of the 'gestalt' conclusion was initially 89% (95%CI 86-91%) and increased to 93% (95%CI 91-95%) after detailed image examination.

CONCLUSION

Standardised assessment of arterial wall FDG uptake intensity, preferably combined with assessment of arterial calcifications into a scoring method, enables accurate, but not perfect, distinction between large artery vasculitis and atherosclerosis.

Diagnostics of atherosclerosis: Overview of the existing methods

Atherosclerosis was and remains an extremely common and serious health problem. Since the elderly are most at risk of cardiovascular risk, and the average life expectancy is increasing, the spread of atherosclerosis and its consequences increases as well. One of the features of atherosclerosis is its asymptomaticity. This factor makes it difficult to make a timely diagnosis. This entails the lack of timely treatment and even prevention. To date, in the arsenal of physicians, there is only a limited set of methods to suspect and fully diagnose atherosclerosis. In this review, we have tried to briefly describe the most common and effective methods for diagnosing atherosclerosis.

Imaging and Hemodynamic Characteristics of Vulnerable Carotid Plaques and Artificial Intelligence Applications in Plaque Classification and Segmentation

Stroke is a massive public health problem. The rupture of vulnerable carotid atherosclerotic plaques is the most common cause of acute ischemic stroke (AIS) across the world. Currently, vessel wall high-resolution magnetic resonance imaging (VW-HRMRI) is the most appropriate and cost-effective imaging technique to characterize carotid plaque vulnerability and plays an important role in promoting early diagnosis and guiding aggressive clinical therapy to reduce the risk of plaque rupture and AIS. In recent years, great progress has been made in imaging research on vulnerable carotid plaques. This review summarizes developments in the imaging and hemodynamic characteristics of vulnerable carotid plaques on the basis of VW-HRMRI and four-dimensional (4D) flow MRI, and it discusses the relationship between these characteristics and ischemic stroke. In addition, the applications of artificial intelligence in plaque classification and segmentation are reviewed.

Arterial wall inflammation is increased in rheumatoid arthritis compared with osteoarthritis, as a marker of early atherosclerosis

Objective

RA is associated with higher risk of cardiovascular (CV) disease. Ongoing systemic inflammation is presumed to accelerate atherosclerosis by increasing inflammation in the arterial wall. However, evidence supporting this hypothesis is limited. We aimed to investigate arterial wall inflammation in RA vs OA, and its association with markers of inflammation and CV risk factors.

Methods

18-fluorodeoxyglucose PET combined with CT (¹⁸F-FDG-PET/CT) was performed in RA (n = 61) and OA (n = 28) to investigate inflammatory activity in the wall of large arteries. Secondary analyses were performed in patients with early untreated RA (n = 30), and established RA, active under DMARD treatment (n = 31) vs OA.

Results

Patients with RA had significantly higher ¹⁸F-FDG uptake in the wall of the carotid arteries (beta 0.27, 95%CI 0.11—0.44, P <0.01) and the aorta (beta 0.47, 95%CI 0.17—0.76, P <0.01) when compared with OA, which persisted after adjustment for traditional CV risk factors. Patients with early RA had the highest ¹⁸F-FDG uptake, followed by patients with established RA and OA respectively. Higher ESR and DAS of 28 joints values were associated with higher ¹⁸F-FDG uptake in all arterial segments.

Conclusion

Patients with RA have increased ¹⁸F-FDG uptake in the arterial wall compared with patients with OA, as a possible marker of early atherosclerosis. Furthermore, a higher level of clinical disease activity and circulating inflammatory markers was associated with higher arterial ¹⁸F-FDG uptake, which may support a role of arterial wall inflammation in the pathogenesis of vascular complications in patients with RA.

Multimodality molecular imaging: Gaining insights into the mechanisms linking chronic stress to cardiovascular disease

Positron emission tomography (PET) imaging can yield unique mechanistic insights into the pathophysiology of atherosclerosis. 18F-fluorodeoxyglucose (18F-FDG), a radiolabeled glucose analog, is retained by cells in proportion to their glycolytic activity. While 18F-FDG accumulates within several cell types in the arterial wall, its retention correlates with macrophage content, providing an index of arterial inflammation (ArtI) which predicts subsequent cardiovascular disease (CVD) events. Furthermore, 18F-FDG-PET imaging allows the simultaneous assessment of metabolic activity in several tissues (e.g., brain, bone marrow) and is performed in conjunction with cross-sectional imaging that enables multi-organ structural assessments. Accordingly, 18F-FDG-PET/computed tomography (CT) imaging facilitates evaluation of disease pathways that span multiple organ systems. Within this paradigm, 18F-FDG-PET/CT imaging has been implemented to study the mechanism linking chronic stress to CVD. To evaluate this, stress-associated neural activity can be quantified (as metabolic activity of the amygdala (AmygA)), while leukopoietic activity, ArtI, and coronary plaque burden are assessed concurrently. Such simultaneous quantification of tissue structures and activities enables the evaluation of multi-organ pathways with the aid of mediation analysis. Using this approach, multi-system 18F-FDG-PET/CT imaging studies have demonstrated that chronically heightened stress-associated neurobiological activity promotes leukopoietic activity and systemic inflammation. This in turn fuels more ArtI and greater non-calcified coronary plaque burden, which result in more CVD events. Subsequent studies have revealed that common stressors, such as chronic noise exposure and income disparities, drive the front end of this pathway to increase CVD risk. Hence, multi-tissue multimodality imaging serves as a powerful tool to uncover complex disease mechanisms.

Arterial wall inflammation in rheumatoid arthritis is reduced by anti-inflammatory treatment

BACKGROUND

Rheumatoid arthritis (RA) patients have an increased risk of cardiovascular disease (CVD), partly due to an increased prevalence of cardiovascular risk factors, but also due to chronic systemic inflammation inducing atherosclerotic changes of the arterial wall. The aim of this study was to determine whether anti-inflammatory therapy for the treatment of RA has favorable effects on arterial wall inflammation in RA patients.

METHODS

Arterial wall inflammation before and after 6 months of anti-inflammatory treatment was assessed in 49 early and established RA patients using 18F-fluorodeoxyglucose-positron emission tomography with computed tomography (18F-FDG-PET/CT). Arterial 18F-FDG uptake was quantified as maximum standardized uptake value (SUVmax) in the thoracic aorta, abdominal aorta, carotid, iliac and femoral arteries. Early RA patients (n = 26) were treated with conventional synthetic disease modifying anti-rheumatic drugs with or without corticosteroids, whereas established RA patients (n = 23) were treated with adalimumab.

RESULTS

In RA patients, overall SUVmax was over time reduced by 4% (difference -0.06, 95%CI -0.12 to -0.01, p = 0.02), with largest reductions in carotid (-8%, p = 0.001) and femoral arteries (-7%, p = 0.005). There was no difference in arterial wall inflammation change between early and established RA patients (SUVmax difference 0.003, 95%CI -0.11 to 0.12, p = 0.95). Change in arterial wall inflammation significantly correlated with change in serological inflammatory markers (erythrocyte sedimentation rate and C-reactive protein).

CONCLUSION

Arterial wall inflammation in RA patients is reduced by anti-inflammatory treatment and this reduction correlates with reductions of serological inflammatory markers. These results suggest that anti-inflammatory treatment of RA has favorable effects on the risk of cardiovascular events in RA patients.

Inter-reader agreement of 18F-FDG PET/CT for the quantification of carotid artery plaque inflammation

Introduction

A significant proportion of ischemic strokes are caused by emboli from unstable atherosclerotic carotid artery plaques. Inflammation is a key feature of plaque instability. Positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-(¹⁸F)-fluoro-D-glucose (¹⁸F-FDG) is a promising technique to quantify plaque inflammation, but a consensus on the methodology has not been established. High inter-reader agreement is essential if ¹⁸F-FDG PET/CT is to be used as a clinical tool for the assessment of unstable plaques and stroke risk.

Methods

We assessed the inter-reader variability of different methods for quantification of ¹⁸F-FDG uptake in 43 patients with carotid artery stenosis ≥70%. Two independent readers delineated the plaque and collected maximum standardized uptake value (SUV_max) from all axial PET slices containing the atherosclerotic plaque.

Results

Uptake values with and without background correction were calculated and intraclass correlation coefficients were highest for uncorrected uptake values (0.97–0.98) followed by those background corrected by subtraction (0.89–0.94) and lowest for those background corrected by division (0.74–0.79).

Conclusion

Quantification methods without background correction have the highest inter-reader agreement for ¹⁸F-FDG PET of carotid artery plaque inflammation. The use of the single highest uptake value (max SUV_max) from the plaque will facilitate the method’s clinical utility in stroke prevention.

Hybrid PET- and MR-driven attenuation correction for enhanced 18F-NaF and 18F-FDG quantification in cardiovascular PET/MR imaging

BACKGROUND

The standard MR Dixon-based attenuation correction (AC) method in positron emission tomography/magnetic resonance (PET/MR) imaging segments only the air, lung, fat and soft-tissues (4-class), thus neglecting the highly attenuating bone tissues and affecting quantification in bones and adjacent vessels. We sought to address this limitation by utilizing the distinctively high bone uptake rate constant Ki expected from 18F-Sodium Fluoride (18F-NaF) to segment bones from PET data and support 5-class hybrid PET/MR-driven AC for 18F-NaF and 18F-Fluorodeoxyglucose (18F-FDG) PET/MR cardiovascular imaging.

METHODS

We introduce 5-class Ki/MR-AC for (i) 18F-NaF studies where the bones are segmented from Patlak Ki images and added as the 5th tissue class to the MR Dixon 4-class AC map. Furthermore, we propose two alternative dual-tracer protocols to permit 5-class Ki/MR-AC for (ii) 18F-FDG-only data, with a streamlined simultaneous administration of 18F-FDG and 18F-NaF at 4:1 ratio (R4:1), or (iii) for 18F-FDG-only or both 18F-FDG and 18F-NaF dual-tracer data, by administering 18F-NaF 90 minutes after an equal 18F-FDG dosage (R1:1). The Ki-driven bone segmentation was validated against computed tomography (CT)-based segmentation in rabbits, followed by PET/MR validation on 108 vertebral bone and carotid wall regions in 16 human volunteers with and without prior indication of carotid atherosclerosis disease (CAD).

RESULTS

In rabbits, we observed similar (< 1.2% mean difference) vertebral bone 18F-NaF SUVmean scores when applying 5-class AC with Ki-segmented bone (5-class Ki/CT-AC) vs CT-segmented bone (5-class CT-AC) tissue. Considering the PET data corrected with continuous CT-AC maps as gold-standard, the percentage SUVmean bias was reduced by 17.6% (18F-NaF) and 15.4% (R4:1) with 5-class Ki/CT-AC vs 4-class CT-AC. In humans without prior CAD indication, we reported 17.7% and 20% higher 18F-NaF target-to-background ratio (TBR) at carotid bifurcations wall and vertebral bones, respectively, with 5- vs 4-class AC. In the R4:1 human cohort, the mean 18F-FDG:18F-NaF TBR increased by 12.2% at carotid bifurcations wall and 19.9% at vertebral bones. For the R1:1 cohort of subjects without CAD indication, mean TBR increased by 15.3% (18F-FDG) and 15.5% (18F-NaF) at carotid bifurcations and 21.6% (18F-FDG) and 22.5% (18F-NaF) at vertebral bones. Similar TBR enhancements were observed when applying the proposed AC method to human subjects with prior CAD indication.

CONCLUSIONS

Ki-driven bone segmentation and 5-class hybrid PET/MR-driven AC is feasible and can significantly enhance 18F-NaF and 18F-FDG contrast and quantification in bone tissues and carotid walls.

Carotid plaque imaging profiling in subjects with risk factors (diabetes and hypertension)

Carotid artery stenosis (CAS) due to the presence of atherosclerotic plaque (AP) is a frequent medical condition and a known risk factor for stroke, and it is also known from literature that several risk factors promote the AP development, in particular aging, smoke, male sex, hypertension, hyperlipidemia, smoke, diabetes type 1 and 2, and genetic factors. The study of carotid atherosclerosis is continuously evolving: even if the strategies of treatment still depends mainly on the degree of stenosis (DoS) determined by the plaque, in the last years the attention has moved to the study of the plaque components in order to identify the so called "vulnerable" plaque: features like the fibrous cap status and thickness, the volume of the lipid-rich necrotic core and the presence of intraplaque hemorrhage (IPH) are risk factors for plaque rupture, that can be studied with modern imaging techniques. The aim of this review is to give a general overview of the principle histological and imaging features of the subcomponent of carotid AP (CAP), focalizing in particular on the features of CAP of patients affected by hypertension and diabetes (in particular type 2 diabetes mellitus).

Carotid plaque imaging and the risk of atherosclerotic cardiovascular disease

Carotid artery plaque is a measure of atherosclerosis and is associated with future risk of atherosclerotic cardiovascular disease (ASCVD), which encompasses coronary, cerebrovascular, and peripheral arterial diseases. With advanced imaging techniques, computerized tomography (CT) and magnetic resonance imaging (MRI) have shown their potential superiority to routine ultrasound to detect features of carotid plaque vulnerability, such as intraplaque hemorrhage (IPH), lipid-rich necrotic core (LRNC), fibrous cap (FC), and calcification. The correlation between imaging features and histological changes of carotid plaques has been investigated. Imaging of carotid features has been used to predict the risk of cardiovascular events. Other techniques such as nuclear imaging and intra-vascular ultrasound (IVUS) have also been proposed to better understand the vulnerable carotid plaque features. In this article, we review the studies of imaging specific carotid plaque components and their correlation with risk scores.

Cohort profile: BIOVASC-late, a prospective multicentred study of imaging and blood biomarkers of carotid plaque inflammation and risk of late vascular recurrence after non-severe stroke in Ireland

PURPOSE

Inflammation is important in stroke. Anti-inflammatory therapy reduces vascular events in coronary patients. ¹⁸F-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) identifies plaque inflammation-related metabolism. However, long-term prospective cohort studies investigating the association between carotid plaque inflammation, identified on ¹⁸F-FDG PET and the risk of recurrent vascular events, have not yet been undertaken in patients with stroke.

PARTICIPANTS

The Biomarkers Imaging Vulnerable Atherosclerosis in Symptomatic Carotid disease (BIOVASC) study and Dublin Carotid Atherosclerosis Study (DUCASS) are two prospective multicentred observational cohort studies, employing near-identical methodologies, which recruited 285 patients between 2008 and 2016 with non-severe stroke/transient ischaemic attack and ipsilateral carotid stenosis (50%-99%). Patients underwent coregistered carotid ¹⁸F-FDG PET/CT angiography and phlebotomy for measurement of inflammatory cytokines. Plaque ¹⁸F-FDG-uptake is expressed as maximum standardised uptake value (SUV_max) and tissue-to-background ratio. The BIOVASC-Late study is a follow-up study (median 7 years) of patients recruited to the DUCASS/BIOVASC cohorts.

FINDINGS TO DATE

We have reported that ¹⁸F-FDG-uptake in atherosclerotic plaques of patients with symptomatic carotid stenosis predicts early recurrent stroke, independent of luminal narrowing. The incorporation of ¹⁸F-FDG plaque uptake into a clinical prediction model also improves discrimination of early recurrent stroke, when compared with risk stratification by luminal stenosis alone. However, the relationship between ¹⁸F-FDG-uptake and late vascular events has not been investigated to date.

FUTURE PLANS

The primary aim of BIOVASC-Late is to investigate the association between SUV_max in symptomatic 'culprit' carotid plaque (as a marker of systemic inflammatory atherosclerosis) and the composite outcome of any late major vascular event (recurrent ischaemic stroke, coronary event or vascular death). Secondary aims are to investigate associations between: (1) SUV_max in symptomatic plaque, and individual vascular endpoints (2) SUV_max in asymptomatic contralateral carotid plaque and SUV_max in ipsilateral symptomatic plaque (3) SUV_max in asymptomatic carotid plaque and major vascular events (4) inflammatory cytokines and vascular events.

Molecular imaging of carotid artery atherosclerosis with PET: a systematic review

PURPOSE

To conduct a systematic review of articles on PET imaging of carotid atherosclerosis with emphasis on clinical usefulness and comparison with other imaging modalities.

METHODS

Research articles reporting carotid artery PET imaging with different radiotracers until 30 November 2018 were systematically searched for in Medline/PubMed, Scopus, Embase, Google Scholar, and Cochrane Library. Duplicates were removed, and editorials, case studies, and investigations on feasibility or reproducibility of PET imaging and of patients with end-stage diseases or immunosuppressive medications were omitted. After quality assessment of included articles using Joanna Briggs Institute checklists, all eligible articles were reviewed.

RESULTS

Of 1718 primary hits, 53 studies comprising 4472 patients, aged 47-91 years (78.8% males), were included and grouped under the following headlines: diagnostic performance, risk factors, laboratory findings, imaging modalities, and treatment. 18F-fluorodeoxyglucose (FDG) (49/53) and 18F-sodium fluoride (NaF) (5/53) were the most utilized tracers to visualize carotid wall inflammation and microcalcification, respectively. Higher carotid FDG uptake was demonstrated in patients with than without symptomatic carotid atherosclerosis. Normal carotid arteries presented with the lowest FDG uptake. In symptomatic atherosclerosis, carotid arteries ipsilateral to a cerebrovascular event had higher FDG uptake than the contralateral carotid artery. FDG uptake was significantly associated with age, male gender, and body mass index in healthy individuals, and in addition with arterial hypertension, hypercholesterolemia, and diabetes mellitus in patients. Histological assessment indicated a strong correlation between microcalcification and NaF uptake in symptomatic patients. Histological evidence of calcification correlated inversely with FDG uptake, which was associated with increased macrophage and CD68 count, both accounting for increased local inflammatory response.

CONCLUSION

FDG-PET visualizes the inflammatory part of carotid atherosclerosis enabling risk stratification to a certain degree, whereas NaF-PET seems to indicate long-term consequences of ongoing inflammation by demonstrating microcalcification allowing discrimination of atherosclerotic from normal arteries and suggesting clinically significant carotid atherosclerosis.

Review of cardiovascular imaging in the Journal of Nuclear Cardiology 2019: Positron emission tomography, computed tomography and magnetic resonance

In 2019, the Journal of Nuclear Cardiology published excellent articles pertaining to imaging in patients with cardiovascular disease. In this review we will summarize a selection of these articles to provide a concise review of the main advancements that have recently occurred in the field and provide the reader with an opportunity to review a wide selection of articles. In this first article of this 2-part series we will focus on publications dealing with positron emission tomography, computed tomography and magnetic resonance. We will specifically discuss imaging as it relates to coronary artery disease, atherosclerosis and inflammation, coronary artery calcification, cardiomyopathies, cardiac implantable electronic devices, prosthetic valves, and left ventricular assist devices. The second part of this review will place emphasis on myocardial perfusion imaging using single-photon emission computed tomography.

Effects of Focal Radiation on [18 F]-Fluoro-D-Glucose Positron Emission Tomography in the Brains of Miniature Pigs: Preliminary Findings on Local Metabolism

OBJECTIVES

It would be a medically important advance if durable and focal neuromodulation of the brain could be delivered noninvasively and without ablation. This ongoing study seeks to elucidate the effects of precisely delivered ionizing radiation upon focal brain metabolism and the corresponding cellular integrity at that target. We hypothesize that focally delivered ionizing radiation to the brain can yield focal metabolic changes without lesioning the brain in the process.

MATERIALS AND METHODS

We used stereotactic radiosurgery to deliver doses from 10 Gy to 120 Gy to the left primary motor cortex (M1) of Lee Sung miniature pigs (n = 8). One additional animal served as a nonirradiated control. We used positron emission tomography-computed tomography (PET-CT) to quantify radiation dose-dependent effects by calculating the ratio of standard uptake values (SUV) of 2-deoxy-2-[¹⁸ F]-fluoro-D-glucose (¹⁸ F-FDG) between the radiated (left) and irradiated (right) hemispheres across nine months.

RESULTS

We found that the FDG-PET SUV ratio at the targeted M1 was significantly lowered from the pre-radiation baseline measurements for animals receiving 60 Gy or higher, with the effect persisting at nine months after radiosurgery. Only at 120 Gy was a lesion suggesting ablation visible at the M1 target. Animals treated at 60-100 Gy showed a reduced signal in the absence of an identifiable lesion, a result consistent with the occurrence of neuromodulation.

CONCLUSION

Focal, noninvasive, and durable changes in brain activity can be induced without a magnetic resonance imaging (MRI)-visible lesion, a result that may be consistent with the occurrence of neuromodulation. This approach may provide new venues for the investigation of neuromodulatory treatments for disorders involving dysfunctional brain circuits. Postmortem pathological analysis is needed to elucidate whether there have been morphological changes not detected by MRI.

Novel PET and Near Infrared Imaging Probes for the Specific Detection of Bacterial Infections Associated With Cardiac Devices

OBJECTIVES

The aim of this study was to develop imaging agents to detect early stage infections in implantable cardiac devices.

BACKGROUND

Bacteria ingest maltodextrins through the specific maltodextrin transporter. We developed probes conjugated with either a fluorescent dye (maltohexaose fluorescent dye probe [MDP]) or a F-18 (F18 fluoromaltohexaose) and determined their usefulness in a model of infections associated with implanted cardiac devices.

METHODS

Stainless steel mock-ups of medical devices were implanted subcutaneously in rats. On post-operative day 4, animals were injected with either Staphylococcus aureus around the mock-ups to induce a relatively mild infection or oil of turpentine to induce noninfectious inflammation. Animals with a sterile implant were used as control subjects. On post-operative day 6, either the MDP or F18 fluoromaltohexaose was injected intravenously, and the animals were scanned with the appropriate imaging device. Additional positron emission tomography imaging studies were performed with F18-fluorodeoxyglucose as a comparison of the specificity of our probes (n = 5 to 9 per group).

RESULTS

The accumulation of the MDP in the infected rats was significantly increased at 1 h after injection when compared with the control and noninfectious inflammation groups (intensity ratio 1.54 ± 0.07 vs. 1.26 ± 0.04 and 1.20 ± 0.05, respectively; p < 0.05) and persisted for more than 24 h. In positron emission tomography imaging, both F18 fluoromaltohexaose and F18 fluorodeoxyglucose significantly accumulated in the infected area 30 min after the injection (maximum standard uptake value ratio 4.43 ± 0.30 and 4.87 ± 0.28, respectively). In control rats, there was no accumulation of imaging probes near the device. In the noninfectious inflammation rats, no significant accumulation was observed with F18 fluoromaltohexaose, but F18 fluorodeoxyglucose accumulated in the mock-up area (maximum standard uptake value 2.53 ± 0.39 vs. 4.74 ± 0.46, respectively; p < 0.05).

CONCLUSIONS

Our results indicate that maltohexaose-based imaging probes are potentially useful for the specific and sensitive diagnosis of infections associated with implantable cardiac devices.