PET/MRI of hypoxia and vascular function in ER-positive breast cancer: correlations with immunohistochemistry

OBJECTIVES

To explore the relationship between indices of hypoxia and vascular function from 18F-fluoromisonidazole ([18F]-FMISO)-PET/MRI with immunohistochemical markers of hypoxia and vascularity in oestrogen receptor-positive (ER +) breast cancer.

METHODS

Women aged  > 18 years with biopsy-confirmed, treatment-naïve primary ER + breast cancer underwent [18F]-FMISO-PET/MRI prior to surgery. Parameters of vascular function were derived from DCE-MRI using the extended Tofts model, whilst hypoxia was assessed using the [18F]-FMISO influx rate constant, Ki. Histological tumour sections were stained with CD31, hypoxia-inducible factor (HIF)-1α, and carbonic anhydrase IX (CAIX). The number of tumour microvessels, median vessel diameter, and microvessel density (MVD) were obtained from CD31 immunohistochemistry. HIF-1α and CAIX expression were assessed using histoscores obtained by multiplying the percentage of positive cells stained by the staining intensity. Regression analysis was used to study associations between imaging and immunohistochemistry variables.

RESULTS

Of the lesions examined, 14/22 (64%) were ductal cancers, grade 2 or 3 (19/22; 86%), with 17/22 (77%) HER2-negative. [18F]-FMISO Ki associated negatively with vessel diameter (p = 0.03), MVD (p = 0.02), and CAIX expression (p = 0.002), whilst no significant relationships were found between DCE-MRI pharmacokinetic parameters and immunohistochemical variables. HIF-1α did not significantly associate with any PET/MR imaging indices.

CONCLUSION

Hypoxia measured by [18F]-FMISO-PET was associated with increased CAIX expression, low MVD, and smaller vessel diameters in ER + breast cancer, further corroborating the link between inadequate vascularity and hypoxia in ER + breast cancer.

KEY POINTS

• Hypoxia, measured by [18F]-FMISO-PET, was associated with low microvessel density and small vessel diameters, corroborating the link between inadequate vascularity and hypoxia in ER + breast cancer. • Increased CAIX expression was associated with higher levels of hypoxia measured by [18F]-FMISO-PET. • Morphologic and functional abnormalities of the tumour microvasculature are the major determinants of hypoxia in cancers and support the previously reported perfusion-driven character of hypoxia in breast carcinomas.

Somatostatin Receptor PET/MR Imaging of Inflammation in Patients With Large Vessel Vasculitis and Atherosclerosis

BACKGROUND

Assessing inflammatory disease activity in large vessel vasculitis (LVV) can be challenging by conventional measures.

OBJECTIVES

We aimed to investigate somatostatin receptor 2 (SST2) as a novel inflammation-specific molecular imaging target in LVV.

METHODS

In a prospective, observational cohort study, in vivo arterial SST2 expression was assessed by positron emission tomography/magnetic resonance imaging (PET/MRI) using 68Ga-DOTATATE and 18F-FET-βAG-TOCA. Ex vivo mapping of the imaging target was performed using immunofluorescence microscopy; imaging mass cytometry; and bulk, single-cell, and single-nucleus RNA sequencing.

RESULTS

Sixty-one participants (LVV: n = 27; recent atherosclerotic myocardial infarction of ≤2 weeks: n = 25; control subjects with an oncologic indication for imaging: n = 9) were included. Index vessel SST2 maximum tissue-to-blood ratio was 61.8% (P < 0.0001) higher in active/grumbling LVV than inactive LVV and 34.6% (P = 0.0002) higher than myocardial infarction, with good diagnostic accuracy (area under the curve: ≥0.86; P < 0.001 for both). Arterial SST2 signal was not elevated in any of the control subjects. SST2 PET/MRI was generally consistent with 18F-fluorodeoxyglucose PET/computed tomography imaging in LVV patients with contemporaneous clinical scans but with very low background signal in the brain and heart, allowing for unimpeded assessment of nearby coronary, myocardial, and intracranial artery involvement. Clinically effective treatment for LVV was associated with a 0.49 ± 0.24 (standard error of the mean [SEM]) (P = 0.04; 22.3%) reduction in the SST2 maximum tissue-to-blood ratio after 9.3 ± 3.2 months. SST2 expression was localized to macrophages, pericytes, and perivascular adipocytes in vasculitis specimens, with specific receptor binding confirmed by autoradiography. SSTR2-expressing macrophages coexpressed proinflammatory markers.

CONCLUSIONS

SST2 PET/MRI holds major promise for diagnosis and therapeutic monitoring in LVV. (PET Imaging of Giant Cell and Takayasu Arteritis [PITA], NCT04071691; Residual Inflammation and Plaque Progression Long-Term Evaluation [RIPPLE], NCT04073810).

Imaging of post-infarct myocardial inflammation with 68Ga-DOTATATE PET/MRI

Background

After myocardial infarction (MI), inflammation and its resolution modulate the extent of myocardial damage. 68Ga-DOTATATE is a PET tracer that binds to somatostatin receptor 2 (SST2), which is up-regulated in pro-inflammatory macrophages [1].

Purpose

We investigated 68Ga-DOTATATE PET/MRI for quantifying post-infarct myocardial inflammation.

Methods

In this prospective observational cohort study, participants with MI underwent 68Ga-DOTATATE PET/MRI at baseline (t0: &lt;2 weeks post-MI) and 3 months (t3M). Patients with prior MI, heart failure, coronary revascularisation, or contraindication to PET/MRI, were excluded. Blood samples were taken at the time of imaging for high sensitivity CRP (hsCRP), high sensitivity troponin I (hsTnI), NTproBNP and peripheral blood monocyte subset counts measured by mass cytometry. 68Ga-DOTATATE maximum Standardised Uptake Values (SUV) and Tissue-to-Background Ratios (TBR) adjusted for blood pool activity were compared in the infarct defined by late gadolinium enhancement (LGE) MRI to remote myocardium at t0 and t3M.

Results

Thirty-two patients (mean age 59 [SD 9] years; 26 [81%] male and 6 [19%] female), comprised of 18 (56%) patients with ST elevation MI and 14 (44%) with non-ST elevation MI, were enrolled. Mean peak troponin was 16,953ng/L (range 408 to &gt;25,000ng/L), and 16 (52%) patients had left ventricular impairment (ejection fraction &lt;50%).

68Ga-DOTATATE PET signal co-localised with myocardial LGE and focal oedema (arrows) on T2-weighted MRI (Fig. 1; asterisk: culprit artery) and had excellent ability to discriminate infarct from remote regions (t0: infarct SUV 2.41 vs. remote 1.58, p&lt;0.0001; t0: infarct TBR 5.08 vs. 3.35, p&lt;0.0001; Fig. 2a).

At 100 (SD 13) days after MI (n=23 patients), residual 68Ga-DOTATATE uptake in the infarct remained higher than remote myocardium (t3M: infarct SUV 1.88 vs. remote 1.27, p&lt;0.0001; t3M: infarct TBR 3.96 vs. remote 2.73, p&lt;0.0001), but was reduced compared to baseline (SUV −22%, p&lt;0.0001; TBR −22%, p=0.002; Fig. 2b).

Reduction in infarct 68Ga-DOTATATE uptake was consistent with overall decreases in hsCRP (2.16 vs. 8.76 mg/L), hsTnI (19 vs. 1365 ng/L) and NTproBNP (372 vs. 959 pg/mL) at t3M vs. t0 (n=23, all p&lt;0.05). Focal oedema on MRI was resolved in 17 (74%) patients at t3M. Infarct-to-remote TBR ratio at t0 was correlated with hsTnI (r=0.35, p&lt;0.05). At t3M (n=9 samples) vs t0 (n=20 samples), there was a reduction in % classical-to-non-classical ratio of peripheral monocytes (mean 6.5 [SD 3.8] vs. 14.4 [SD 11.2], p=0.005).

Conclusions

This is the first prospective study of serial 68Ga-DOTATATE PET/MRI in patients after MI. Here we show that 68Ga-DOTATATE tracks resolving myocardial inflammation. Ongoing work as part of this study seeks to confirm the cellular origin of infarct-related 68Ga-DOTATATE PET signal and SST2 expression within inflamed myocardial tissue, and test its longer-term association with ischaemic myocardial remodelling.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Wellcome TrustBritish Heart Foundation

An optoacoustic imaging feature set to characterise blood vessels surrounding benign and malignant breast lesions

Combining optoacoustic (OA) imaging with ultrasound (US) enables visualisation of functional blood vasculature in breast lesions by OA to be overlaid with the morphological information of US. Here, we develop a simple OA feature set to differentiate benign and malignant breast lesions. 94 female patients with benign, indeterminate or suspicious lesions were recruited and underwent OA-US. An OA-US imaging feature set was developed using images from the first 38 patients, which contained 14 malignant and 8 benign solid lesions. Two independent radiologists blindly scored the OA-US images of a further 56 patients, which included 31 malignant and 13 benign solid lesions, with a sensitivity of 96.8% and specificity of 84.6%. Our findings indicate that OA-US can reveal vascular patterns of breast lesions that indicate malignancy using a simple feature set based on single wavelength OA data, which is therefore amenable to application in low resource settings for breast cancer management.

[18F]-AV-1451 binding in the substantia nigra as a marker of neuromelanin in Lewy body diseases

While [¹⁸F]-AV-1451 was developed as a PET radiotracer with high affinity for hyperphosphorylated tau, it has been proposed that loss of 'off-target' [¹⁸F]-AV-1451 binding to neuromelanin in the substantia nigra could be a surrogate marker of Lewy body diseases. [¹⁸F]-AV-1451 binding was measured in the substantia nigra of patients with Parkinson's disease (n = 35), dementia with Lewy bodies (n = 10) and separate control groups (n = 37; n = 14). Associations with motor symptoms, cognition and disease duration were evaluated using linear regression models. The dementia with Lewy bodies group had significantly reduced substantia nigra [¹⁸F]-AV-1451 binding compared to controls after adjusting for age (P < 0.05). However, there were no significant differences in substantia nigra [¹⁸F]-AV-1451 binding between Parkinson's disease and controls. Substantia nigra [¹⁸F]-AV-1451 binding was not associated with age, disease duration, Movement Disorders Society-Unified Parkinson's Disease Rating Scale and cognitive scores in dementia with Lewy bodies and Parkinson's disease groups. Despite the reduction of substantia nigra [¹⁸F]-AV-1451 binding in dementia with Lewy bodies, these findings suggest that substantia nigra [¹⁸F]-AV-1451 binding has no value as a diagnostic marker in early Parkinson's disease. Further investigations in longitudinal cohorts are warranted.

Pericoronary and periaortic adipose tissue density are associated with inflammatory disease activity in Takayasu arteritis and atherosclerosis

AIMS

To examine pericoronary adipose tissue (PCAT) and periaortic adipose tissue (PAAT) density on coronary computed tomography angiography for assessing arterial inflammation in Takayasu arteritis (TAK) and atherosclerosis.

METHODS AND RESULTS

PCAT and PAAT density was measured in coronary (n = 1016) and aortic (n = 108) segments from 108 subjects [TAK + coronary artery disease (CAD), n = 36; TAK, n = 18; atherosclerotic CAD, n = 32; matched controls, n = 22]. Median PCAT and PAAT densities varied between groups (mPCAT: P < 0.0001; PAAT: P = 0.0002). PCAT density was 7.01 ± standard error of the mean (SEM) 1.78 Hounsfield Unit (HU) higher in coronary segments from TAK + CAD patients than stable CAD patients (P = 0.0002), and 8.20 ± SEM 2.04 HU higher in TAK patients without CAD than controls (P = 0.0001). mPCAT density was correlated with Indian Takayasu Clinical Activity Score (r = 0.43, P = 0.001) and C-reactive protein (r = 0.41, P < 0.0001) and was higher in active vs. inactive TAK (P = 0.002). mPCAT density above -74 HU had 100% sensitivity and 95% specificity for differentiating active TAK from controls [area under the curve = 0.99 (95% confidence interval 0.97-1)]. The association of PCAT density and coronary arterial inflammation measured by 68Ga-DOTATATE positron emission tomography (PET) equated to an increase of 2.44 ± SEM 0.77 HU in PCAT density for each unit increase in 68Ga-DOTATATE maximum tissue-to-blood ratio (P = 0.002). These findings remained in multivariable sensitivity analyses adjusted for potential confounders.

CONCLUSIONS

PCAT and PAAT density are higher in TAK than atherosclerotic CAD or controls and are associated with clinical, biochemical, and PET markers of inflammation. Owing to excellent diagnostic accuracy, PCAT density could be useful as a clinical adjunct for assessing disease activity in TAK.

[11C]PK11195-PET Brain Imaging of the Mitochondrial Translocator Protein in Mitochondrial Disease

OBJECTIVE

To explore the possibilities of radioligands against the mitochondrial outer membrane translocator protein (TSPO) as biomarkers for mitochondrial disease, we performed brain PET-MRI with [11C]PK11195 in 14 patients with genetically confirmed mitochondrial disease and 33 matched controls.

METHODS

Case-control study of brain PET-MRI with the TSPO radioligand [11C]PK11195.

RESULTS

Forty-six percent of symptomatic patients had volumes of abnormal radiotracer binding greater than the 95th percentile in controls. [11C]PK11195 binding was generally greater in gray matter and significantly decreased in white matter. This was most striking in patients with nuclear TYMP or mitochondrial m.3243A>G MT-TL1 mutations, in keeping with differences in mitochondrial density seen postmortem. Some regional binding patterns corresponded to clinical presentation and underlying mutation, even in the absence of structural changes on MRI. This was most obvious for the cerebellum, where patients with ataxia had decreased binding in the cerebellar cortex, but not necessarily volume loss. Overall, there was a positive correlation between aberrant [11C]PK11195 binding and clinical severity.

CONCLUSION

These findings endorse the use of PET imaging with TSPO radioligands as a noninvasive in vivo biomarker of mitochondrial pathology.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that brain PET-MRI with TSPO radioligands identifies mitochondrial pathology.

Validation of a combined image derived input function and venous sampling approach for the quantification of [18F]GE-179 PET binding in the brain

Blood-based kinetic analysis of PET data relies on an accurate estimate of the arterial plasma input function (PIF). An alternative to invasive measurements from arterial sampling is an image-derived input function (IDIF). However, an IDIF provides the whole blood radioactivity concentration, rather than the required free tracer radioactivity concentration in plasma. To estimate the tracer PIF, we corrected an IDIF from the carotid artery with estimates of plasma parent fraction (PF) and plasma-to-whole blood (PWB) ratio obtained from five venous samples. We compared the combined IDIF+venous approach to gold standard data from arterial sampling in 10 healthy volunteers undergoing [¹⁸F]GE-179 brain PET imaging of the NMDA receptor. Arterial and venous PF and PWB ratio estimates determined from 7 patients with traumatic brain injury (TBI) were also compared to assess the potential effect of medication. There was high agreement between areas under the curves of the estimates of PF (r = 0.99, p<0.001), PWB ratio (r = 0.93, p<0.001), and the PIF (r = 0.92, p<0.001) as well as total distribution volume (V_T) in 11 regions across the brain (r = 0.95, p<0.001). IDIF+venous V_T had a mean bias of -1.7% and a comparable regional coefficient of variation (arterial: 21.3 ± 2.5%, IDIF+venous: 21.5 ± 2.0%). Simplification of the IDIF+venous method to use only one venous sample provided less accurate V_T estimates (mean bias 9.9%; r = 0.71, p<0.001). A version of the method that avoids the need for blood sampling by combining the IDIF with population-based PF and PWB ratio estimates systematically underestimated V_T (mean bias -20.9%), and produced V_T estimates with a poor correlation to those obtained using arterial data (r = 0.45, p<0.001). Arterial and venous blood data from 7 TBI patients showed high correlations for PF (r = 0.92, p = 0.003) and PWB ratio (r = 0.93, p = 0.003). In conclusion, the IDIF+venous method with five venous samples provides a viable alternative to arterial sampling for quantification of [¹⁸F]GE-179 V_T.

In vivo coupling of dendritic complexity with presynaptic density in primary tauopathies

Understanding the cellular underpinnings of neurodegeneration remains a challenge; loss of synapses and dendritic arborization are characteristic and can be quantified in vivo, with [¹¹C]UCB-J PET and MRI-based Orientation Dispersion Imaging (ODI), respectively. We aimed to assess how both measures are correlated, in 4R-tauopathies of progressive supranuclear palsy - Richardson's Syndrome (PSP-RS; n = 22) and amyloid-negative (determined by [¹¹C]PiB PET) Corticobasal Syndrome (Cortiobasal degeneration, CBD; n =14), as neurodegenerative disease models, in this proof-of-concept study. Compared to controls (n = 27), PSP-RS and CBD patients had widespread reductions in cortical ODI, and [¹¹C]UCB-J non-displaceable binding potential (BP_ND) in excess of atrophy. In PSP-RS and CBD separately, regional cortical ODI was significantly associated with [¹¹C]UCB-J BP_ND in disease-associated regions (p < 0.05, FDR corrected). Our findings indicate that reductions in synaptic density and dendritic complexity in PSP-RS and CBD are more severe and extensive than atrophy. Furthermore, both measures are tightly coupled in vivo, furthering our understanding of the pathophysiology of neurodegeneration, and applicable to studies of early neurodegeneration with a safe and widely available MRI platform.

A Modest Increase in 11C-PK11195-Positron Emission Tomography TSPO Binding in Depression Is Not Associated With Serum C-Reactive Protein or Body Mass Index

Background

Immune mechanisms have been implicated in the pathogenesis of depression. Translocator protein (TSPO)–targeted positron emission tomography (PET) has been used to assess neuroinflammation in major depressive disorder. We aimed to 1) test the hypothesis of significant case-control differences in TSPO binding in the anterior cingulate cortex, prefrontal cortex, and insula regions; and 2) explore the relationship between cerebral TSPO binding and peripheral blood C-reactive protein (CRP) concentration.

Methods

A total of 51 depressed subjects with Hamilton Depression Rating Scale score >13 (median 17; interquartile range, 16–22) and 25 healthy control subjects underwent dynamic brain ¹¹C-PK11195 PET and peripheral blood immune marker characterization. Depressed subjects were divided into high CRP (>3 mg/L; n = 20) and low CRP (<3 mg/L; n = 31).

Results

Across the three regions, TSPO binding was significantly increased in depressed versus control subjects (η²_p = .09; F_1,71 = 6.97, p = .01), which was not influenced by body mass index. The case-control difference was greatest in the anterior cingulate cortex (d = 0.49; t₇₄ = 2.00, p = .03) and not significant in the prefrontal cortex or insula (d = 0.27 and d = 0.36, respectively). Following CRP stratification, significantly higher TSPO binding was observed in low-CRP depression compared with controls (d = 0.53; t₅₄ = 1.96, p = .03). These effect sizes are comparable to prior major depressive disorder case-control TSPO PET data. No significant correlations were observed between TSPO and CRP measures.

Conclusions

Consistent with previous findings, there is a modest increase in TSPO binding in depressed patients compared with healthy control subjects. The lack of a significant correlation between brain TSPO binding and blood CRP concentration or body mass index poses questions about the interactions between central and peripheral immune responses in the pathogenesis of depression.

Hypoxia and perfusion in breast cancer: simultaneous assessment using PET/MR imaging

OBJECTIVES

Hypoxia is associated with poor prognosis and treatment resistance in breast cancer. However, the temporally variant nature of hypoxia can complicate interpretation of imaging findings. We explored the relationship between hypoxia and vascular function in breast tumours through combined 18F-fluoromisonidazole (18 F-FMISO) PET/MRI, with simultaneous assessment circumventing the effect of temporal variation in hypoxia and perfusion.

METHODS

Women with histologically confirmed, primary breast cancer underwent a simultaneous 18F-FMISO-PET/MR examination. Tumour hypoxia was assessed using influx rate constant Ki and hypoxic fractions (%HF), while parameters of vascular function (Ktrans, kep, ve, vp) and cellularity (ADC) were derived from dynamic contrast-enhanced (DCE) and diffusion-weighted (DW)-MRI, respectively. Additional correlates included histological subtype, grade and size. Relationships between imaging variables were assessed using Pearson correlation (r).

RESULTS

Twenty-nine women with 32 lesions were assessed. Hypoxic fractions > 1% were observed in 6/32 (19%) cancers, while 18/32 (56%) tumours showed a %HF of zero. The presence of hypoxia in lesions was independent of histological subtype or grade. Mean tumour Ktrans correlated negatively with Ki (r = - 0.38, p = 0.04) and %HF (r = - 0.33, p = 0.04), though parametric maps exhibited intratumoural heterogeneity with hypoxic regions colocalising with both hypo- and hyperperfused areas. No correlation was observed between ADC and DCE-MRI or PET parameters. %HF correlated positively with lesion size (r = 0.63, p = 0.001).

CONCLUSION

Hypoxia measured by 18F-FMISO-PET correlated negatively with Ktrans from DCE-MRI, supporting the hypothesis of perfusion-driven hypoxia in breast cancer. Intratumoural hypoxia-perfusion relationships were heterogeneous, suggesting that combined assessment may be needed for disease characterisation, which could be achieved using simultaneous multimodality imaging.

KEY POINTS

• At the tumour level, hypoxia measured by 18F-FMISO-PET was negatively correlated with perfusion measured by DCE-MRI, which supports the hypothesis of perfusion-driven hypoxia in breast cancer. • No associations were observed between 18F-FMISO-PET parameters and tumour histology or grade, but tumour hypoxic fractions increased with lesion size. • Intratumoural hypoxia-perfusion relationships were heterogeneous, suggesting that the combined hypoxia-perfusion status of tumours may need to be considered for disease characterisation, which can be achieved via simultaneous multimodality imaging as reported here.

Pericoronary adipose tissue density is associated with clinical disease activity in Takayasu arteritis and coronary arterial inflammation measured by 68Ga-DOTATATE PET in atherosclerosis

Background

Coronary artery disease (CAD) is an under-recognized complication of intense arterial inflammation in Takayasu arteritis (TAK). While pericoronary adipose tissue (PCAT) density is associated with arterial inflammation in CAD patients, this relationship has not previously been studied in TAK patients, nor directly compared with coronary arterial inflammation measured by 68Ga-DOTATATE positron emission tomography (PET).

Purpose

To compare PCAT density with clinical, biochemical and molecular imaging markers of inflammation in TAK and CAD patients.

Methods

PCAT density was quantified from computed tomography coronary angiography (CTCA) around each of the 17 coronary segments in patients with: (1) TAK and CAD, (2) atherosclerotic CAD, and (3) age and gender-matched healthy controls, using semi-automated software (Autoplaque). In TAK patients, PCAT density was compared to the Indian Takayasu Clinical Activity Score (ITAS) and high-sensitivity C-reactive protein (CRP). In CAD patients, PCAT density was compared to local arterial inflammation measured by coronary motion-frozen 68Ga-DOTATATE PET using image registration software (FusionQuant), and systemic (aortic) inflammation using 18F-fluorodeoxyglucose (FDG) PET. Data was acquired either during routine clinical care or prior research that established 68Ga-DOTATATE as an experimental marker of arterial inflammation that binds macrophage somatostatin receptor-2 in atherosclerotic plaques (NCT02021188).

Results

60 patients were included (TAK, n=20; CAD, n=20; healthy, n=20). Non-calcified plaque burden (TAK: 95.2%; CAD: 90.4%, p&lt;0.0001) and CRP (TAK: 25.2 ±SD 16.1 mg/L; CAD: 2.5 ±SD 1.7 mg/L, p=0.04) were greater in TAK than CAD patients.

PCAT density varied significantly among the three groups (median [IQR] TAK: −72.9 [−81.2 to -66.1] Hounsfield unit [HU]; CAD: −79.9 [−88.0 to −72.2]; healthy: −83.8 [−90.1 to −75.8] HU, p&lt;0.0001). Figure: box-plot showing the distribution of PCAT values by group, with corresponding representative multiplanar reconstructed and cross-sectional CTCA images with surrounding PCAT density displayed by color table in left anterior descending arteries.

PCAT density was significantly associated with ITAS (r=0.61, p=0.004) and CRP (r=0.43, p=0.03) in TAK patients, and coronary 68Ga-DOTATATE maximum tissue-to-blood ratio (r=0.31, p&lt;0.001) in CAD patients. PCAT density was not associated with aortic 18F-FDG uptake in CAD patients, nor subcutaneous (pre-sternal) adipose tissue density in either disease group. No significant patient-level confounders were identified using linear mixed-effects regression modelling.

Conclusion

PCAT density measured by CTCA is greater in TAK than CAD patients, and is associated with clinical and biochemical markers of disease activity in TAK, and coronary arterial inflammation measured by 68Ga-DOTATATE PET in CAD. PCAT could be a useful, easy to measure marker of coronary inflammation and disease activity in both TAK and CAD.

PCAT density is greater in TAK than CAD

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): Wellcome Trust

Synaptic Loss in Primary Tauopathies Revealed by [11 C]UCB-J Positron Emission Tomography

BACKGROUND

Synaptic loss is a prominent and early feature of many neurodegenerative diseases.

OBJECTIVES

We tested the hypothesis that synaptic density is reduced in the primary tauopathies of progressive supranuclear palsy (PSP) (Richardson's syndrome) and amyloid-negative corticobasal syndrome (CBS).

METHODS

Forty-four participants (15 CBS, 14 PSP, and 15 age-/sex-/education-matched controls) underwent PET with the radioligand [11 C]UCB-J, which binds to synaptic vesicle glycoprotein 2A, a marker of synaptic density; participants also had 3 Tesla MRI and clinical and neuropsychological assessment.

RESULTS

Nine CBS patients had negative amyloid biomarkers determined by [11 C]PiB PET and hence were deemed likely to have corticobasal degeneration (CBD). Patients with PSP-Richardson's syndrome and amyloid-negative CBS were impaired in executive, memory, and visuospatial tasks. [11 C]UCB-J binding was reduced across frontal, temporal, parietal, and occipital lobes, cingulate, hippocampus, insula, amygdala, and subcortical structures in both PSP and CBD patients compared to controls (P < 0.01), with median reductions up to 50%, consistent with postmortem data. Reductions of 20% to 30% were widespread even in areas of the brain with minimal atrophy. There was a negative correlation between global [11 C]UCB-J binding and the PSP and CBD rating scales (R = -0.61, P < 0.002; R = -0.72, P < 0.001, respectively) and a positive correlation with the revised Addenbrooke's Cognitive Examination (R = 0.52; P = 0.01).

CONCLUSIONS

We confirm severe synaptic loss in PSP and CBD in proportion to disease severity, providing critical insight into the pathophysiology of primary degenerative tauopathies. [11 C]UCB-J may facilitate treatment strategies for disease-modification, synaptic maintenance, or restoration. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Detection limit of 89Zr-labeled T cells for cellular tracking: an in vitro imaging approach using clinical PET/CT and PET/MRI

PURPOSE

Tracking cells in vivo using imaging can provide non-invasive information to understand the pharmacology, efficacy, and safety of novel cell therapies. Zirconium-89 (t1/2 = 78.4 h) has recently been used to synthesize [89Zr]Zr(oxinate)4 for cell tracking using positron emission tomography (PET). This work presents an in vitro approach to estimate the detection limit for in vivo PET imaging of Jurkat T cells directly labeled with [89Zr]Zr(oxinate)4 utilizing clinical PET/CT and PET/MRI.

METHODS

Jurkat T cells were labeled with varying concentrations of [89Zr]Zr(oxinate)4 to generate different cell-specific activities (0.43-31.91 kBq/106 cells). Different concentrations of labeled cell suspensions (104, 105, and 106 cells) were seeded on 6-well plates and into a 3 × 3 cubic-well plate with 1 cm3 cubic wells as a gel matrix. Plates were imaged on clinical PET/CT and PET/MRI scanners for 30 min. The total activity in each well was determined by drawing volumes of interest over each well on PET images. The total cell-associated activity was measured using a well counter and correlated with imaging data. Simulations for non-specific signal were performed to model the effect of non-specific radioactivity on detection.

RESULTS

Using this in vitro model, the lowest cell number that could be visualized on 6-well plate images was 6.8 × 104, when the specific activity was 27.8 kBq/106 cells. For the 3 × 3 cubic-well, a plate of 3.3 × 104 cells could be detected on images with a specific activity of 15.4 kBq/106 cells.

CONCLUSION

The results show the feasibility of detecting [89Zr]Zr(oxinate)4-labeled Jurkat T cells on clinical PET systems. The results provide a best-case scenario, as in vivo detection using PET/CT or PET/MRI will be affected by cell number, specific activity per cell, the density of cells within the target volume, and non-specific signal. This work has important implications for cell labeling studies in patients, particularly when using radiosensitive cells (e.g., T cells), which require detection of low cell numbers while minimizing radiation dose per cell.

Quantifying disease activity in rheumatoid arthritis with the TSPO PET ligand 18F-GE-180 and comparison with 18F-FDG and DCE-MRI

Purpose

While the aetiology of rheumatoid arthritis (RA) remains unclear, many of the inflammatory components are well characterised. For diagnosis and therapy evaluation, in vivo insight into these processes would be valuable. Various imaging probes have shown value including dynamic contrast-enhanced (DCE) MRI and PET/CT using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) or tracers targeting the translocator protein (TSPO). To evaluate ¹⁸F-GE-180, a novel TSPO PET tracer, for detecting and quantifying disease activity in RA, we compared ¹⁸F-GE-180 uptake with that of ¹⁸F-FDG and DCE-MRI measures of inflammation.

Methods

Eight RA patients with moderate-to-high, stable disease activity and active disease in at least one wrist were included in this study (NCT02350426). Participants underwent PET/CT examinations with ¹⁸F-GE-180 and ¹⁸F-FDG on separate visits, covering the shoulders and from the pelvis to the feet, including hands and wrists. DCE-MRI was performed on one affected hand. Uptake was compared visually between tracers as judged by an experienced radiologist and quantitatively using the maximum standardised uptake value (SUV_max). Uptake for both tracers was correlated with DCE-MRI parameters of inflammation, including the volume transfer coefficient K^trans using Pearson correlation (r).

Results

PET/CT imaging with ¹⁸F-GE-180 in RA patients showed marked extra-synovial uptake around the affected joints. Overall sensitivity for detecting clinically affected joints was low (14%). ¹⁸F-GE-180 uptake did not or only weakly correlate with DCE-MRI parameters in the wrist (r = 0.09–0.31). ¹⁸F-FDG showed higher sensitivity for detecting symptomatic joints (34%), as well as strong positive correlation with DCE-MRI parameters (SUV_max vs. K^trans: r = 0.92 for wrist; r = 0.68 for metacarpophalangeal joints).

Conclusions

The correlations between DCE-MRI parameters and ¹⁸F-FDG uptake support use of this PET tracer for quantification of inflammatory burden in RA. The TSPO tracer ¹⁸F-GE-180, however, has shown limited use for the investigation of RA due to its poor sensitivity and ability to quantify disease activity in RA.

Optoacoustic Imaging Detects Hormone-Related Physiological Changes of Breast Parenchyma

PURPOSE

 Optoacoustic imaging with ultrasound (OPUS) can assess in-vivo perfusion/oxygenation through surrogate measures of oxy, deoxy and total hemoglobin content in tissues. The primary aim of our study was to evaluate the ability of OPUS to detect physiological changes in the breast during the menstrual cycle and to determine qualitative/quantitative metrics of normal parenchymal tissue in pre-/post-menopausal women. The secondary aim was to assess the technique's repeatability.

MATERIALS AND METHODS

 We performed a prospective ethically approved study in volunteers using OPUS (700, 800 and 850 nm wavelengths) in the proliferative/follicular and secretory phase of the menstrual cycle. Regions of interest (ROIs) were drawn on the most superficial region of fibroglandular tissue and same-day intra-observer repeatability was assessed. We used t-tests to interrogate differences in the OPUS measurements due to hormonal changes and interclass correlation coefficients/Bland-Altman plots to evaluate the repeatability of mean ROI signal intensities.

RESULTS

 22 pre-menopausal and 8 post-menopausal volunteers were recruited. 21 participants underwent repeatability examinations. OPUS intensity values were significantly higher (p < 0.0001) at all excitation wavelengths in the secretory compared to the proliferative/follicular phase. Post-menopausal volunteers showed similar optoacoustic values to the proliferative/follicular phase of pre-menopausal volunteers. The repeatability of the technique was comparable to other handheld ultrasound modalities.

CONCLUSION

 OPUS detects changes in perfusion/vascularity related to the menstrual cycle and menopausal status of breast parenchyma.

Positron emission tomography-guided magnetic resonance spectroscopy in Alzheimer disease

OBJECTIVE

To determine whether the level of metabolites in magnetic resonance spectroscopy (MRS) is a representative marker of underlying pathological changes identified in positron emission tomographic (PET) images in Alzheimer disease (AD).

METHODS

We performed PET-guided MRS in cases of probable AD, mild cognitive impairment (MCI), and healthy controls (HC). All participants were imaged by 11 C-Pittsburgh compound B (11 C-PiB) and 18 F-fluorodeoxyglucose (18 F-FDG) PET followed by 3T MRS. PET images were assessed both visually and using standardized uptake value ratios (SUVRs). MRS voxels were placed in regions with maximum abnormality on amyloid (Aβ+) and FDG (hypometabolic) areas on PET scans. Corresponding normal areas were selected in controls. The ratios of total N-acetyl (tNA) group, myoinositol (mI), choline, and glutamate + glutamine over creatine (Cr) were compared between these regions.

RESULTS

Aβ + regions had significantly higher (p = 0.02) mI/Cr and lower tNA/Cr (p = 0.02), whereas in hypometabolic areas only tNA/Cr was reduced (p = 0.003). Multiple regression analysis adjusting for sex, age, and education showed mI/Cr was only associated with 11 C-PiB SUVR (p < 0.0001). tNA/Cr, however, was associated with both PiB (p = 0.0003) and 18 F-FDG SUVR (p = 0.006). The level of mI/Cr was not significantly different between MCI and AD (p = 0.28), but tNA/Cr showed significant decline from HC to MCI to AD (p = 0.001, p = 0.04).

INTERPRETATION

mI/Cr has significant temporal and spatial associations with Aβ and could potentially be considered as a disease state biomarker. tNA is an indicator of early neurodegenerative changes and might have a role as disease stage biomarker and also as a valuable surrogate marker for treatment response. Ann Neurol 2018;83:771-778.

Imaging Biomarkers in Alzheimer's Disease: A Practical Guide for Clinicians

Although recent developments in imaging biomarkers have revolutionized the diagnosis of Alzheimer’s disease at early stages, the utility of most of these techniques in clinical setting remains unclear. The aim of this review is to provide a clear stepwise algorithm on using multitier imaging biomarkers for the diagnosis of Alzheimer’s disease to be used by clinicians and radiologists for day-to-day practice. We summarized the role of most common imaging techniques and their appropriate clinical use based on current consensus guidelines and recommendations with brief sections on acquisition and analysis techniques for each imaging modality. Structural imaging, preferably MRI or alternatively high resolution CT, is the essential first tier of imaging. It improves the accuracy of clinical diagnosis and excludes other potential pathologies. When the results of clinical examination and structural imaging, assessed by dementia expert, are still inconclusive, functional imaging can be used as a more advanced option. PET with ligands such as amyloid tracers and ¹⁸F-fluorodeoxyglucose can improve the sensitivity and specificity of diagnosis particularly at the early stages of the disease. There are, however, limitations in using these techniques in wider community due to a combination of lack of facilities and expertise to interpret the findings. The role of some of the more recent imaging techniques including tau imaging, functional MRI, or diffusion tensor imaging in clinical practice, remains to be established in the ongoing and future studies.

Detection of Atherosclerotic Inflammation by 68Ga-DOTATATE PET Compared to [18F]FDG PET Imaging

BACKGROUND

Inflammation drives atherosclerotic plaque rupture. Although inflammation can be measured using fluorine-18-labeled fluorodeoxyglucose positron emission tomography ([¹⁸F]FDG PET), [¹⁸F]FDG lacks cell specificity, and coronary imaging is unreliable because of myocardial spillover.

OBJECTIVES

This study tested the efficacy of gallium-68-labeled DOTATATE (⁶⁸Ga-DOTATATE), a somatostatin receptor subtype-2 (SST₂)-binding PET tracer, for imaging atherosclerotic inflammation.

METHODS

We confirmed ⁶⁸Ga-DOTATATE binding in macrophages and excised carotid plaques. ⁶⁸Ga-DOTATATE PET imaging was compared to [¹⁸F]FDG PET imaging in 42 patients with atherosclerosis.

RESULTS

Target SSTR2 gene expression occurred exclusively in "proinflammatory" M1 macrophages, specific ⁶⁸Ga-DOTATATE ligand binding to SST₂ receptors occurred in CD68-positive macrophage-rich carotid plaque regions, and carotid SSTR2 mRNA was highly correlated with in vivo ⁶⁸Ga-DOTATATE PET signals (r = 0.89; 95% confidence interval [CI]: 0.28 to 0.99; p = 0.02). ⁶⁸Ga-DOTATATE mean of maximum tissue-to-blood ratios (mTBR_max) correctly identified culprit versus nonculprit arteries in patients with acute coronary syndrome (median difference: 0.69; interquartile range [IQR]: 0.22 to 1.15; p = 0.008) and transient ischemic attack/stroke (median difference: 0.13; IQR: 0.07 to 0.32; p = 0.003). ⁶⁸Ga-DOTATATE mTBR_max predicted high-risk coronary computed tomography features (receiver operating characteristics area under the curve [ROC AUC]: 0.86; 95% CI: 0.80 to 0.92; p < 0.0001), and correlated with Framingham risk score (r = 0.53; 95% CI: 0.32 to 0.69; p <0.0001) and [¹⁸F]FDG uptake (r = 0.73; 95% CI: 0.64 to 0.81; p < 0.0001). [¹⁸F]FDG mTBR_max differentiated culprit from nonculprit carotid lesions (median difference: 0.12; IQR: 0.0 to 0.23; p = 0.008) and high-risk from lower-risk coronary arteries (ROC AUC: 0.76; 95% CI: 0.62 to 0.91; p = 0.002); however, myocardial [¹⁸F]FDG spillover rendered coronary [¹⁸F]FDG scans uninterpretable in 27 patients (64%). Coronary ⁶⁸Ga-DOTATATE PET scans were readable in all patients.

CONCLUSIONS

We validated ⁶⁸Ga-DOTATATE PET as a novel marker of atherosclerotic inflammation and confirmed that ⁶⁸Ga-DOTATATE offers superior coronary imaging, excellent macrophage specificity, and better power to discriminate high-risk versus low-risk coronary lesions than [¹⁸F]FDG. (Vascular Inflammation Imaging Using Somatostatin Receptor Positron Emission Tomography [VISION]; NCT02021188).

Assessment of early treatment response to neoadjuvant chemotherapy in breast cancer using non-mono-exponential diffusion models: a feasibility study comparing the baseline and mid-treatment MRI examinations

OBJECTIVES

To assess the feasibility of the mono-exponential, bi-exponential and stretched-exponential models in evaluating response of breast tumours to neoadjuvant chemotherapy (NACT) at 3 T.

METHODS

Thirty-six female patients (median age 53, range 32-75 years) with invasive breast cancer undergoing NACT were enrolled for diffusion-weighted MRI (DW-MRI) prior to the start of treatment. For assessment of early response, changes in parameters were evaluated on mid-treatment MRI in 22 patients. DW-MRI was performed using eight b values (0, 30, 60, 90, 120, 300, 600, 900 s/mm2). Apparent diffusion coefficient (ADC), tissue diffusion coefficient (D t), vascular fraction (ƒ), distributed diffusion coefficient (DDC) and alpha (α) parameters were derived. Then t tests compared the baseline and changes in parameters between response groups. Repeatability was assessed at inter- and intraobserver levels.

RESULTS

All patients underwent baseline MRI whereas 22 lesions were available at mid-treatment. At pretreatment, mean diffusion coefficients demonstrated significant differences between groups (p < 0.05). At mid-treatment, percentage increase in ADC and DDC showed significant differences between responders (49 % and 43 %) and non-responders (21 % and 32 %) (p = 0.03, p = 0.04). Overall, stretched-exponential parameters showed excellent repeatability.

CONCLUSION

DW-MRI is sensitive to baseline and early treatment changes in breast cancer using non-mono-exponential models, and the stretched-exponential model can potentially monitor such changes.

KEY POINTS

• Baseline diffusion coefficients demonstrated significant differences between complete pathological responders and non-responders. • Increase in ADC and DDC at mid-treatment can discriminate responders and non-responders. • The ƒ fraction at mid-treatment decreased in responders whereas increased in non-responders. • The mono- and stretched-exponential models showed excellent inter- and intrarater repeatability. • Treatment effects can potentially be assessed by non-mono-exponential diffusion models.

Brain hypoxia mapping in acute stroke: Back-to-back T2' MR versus 18F-fluoromisonidazole PET in rodents

Background Mapping the hypoxic brain in acute ischemic stroke has considerable potential for both diagnosis and treatment monitoring. PET using ¹⁸F-fluoro-misonidazole (FMISO) is the reference method; however, it lacks clinical accessibility and involves radiation exposure. MR-based T2' mapping may identify tissue hypoxia and holds clinical potential. However, its validation against FMISO imaging is lacking. Here we implemented back-to-back FMISO-PET and T2' MR in rodents subjected to acute middle cerebral artery occlusion. For direct clinical relevance, regions of interest delineating reduced T2' signal areas were manually drawn. Methods Wistar rats were subjected to filament middle cerebral artery occlusion, immediately followed by intravenous FMISO injection. Multi-echo T2 and T2* sequences were acquired twice during FMISO brain uptake, interleaved with diffusion-weighted imaging. Perfusion-weighted MR was also acquired whenever feasible. Immediately following MR, PET data reflecting the history of FMISO brain uptake during MR acquisition were acquired. T2' maps were generated voxel-wise from T2 and T2*. Two raters independently drew T2' lesion regions of interest. FMISO uptake and perfusion data were obtained within T2' consensus regions of interest, and their overlap with the automatically generated FMISO lesion and apparent diffusion coefficient lesion regions of interest was computed. Results As predicted, consensus T2' lesion regions of interest exhibited high FMISO uptake as well as substantial overlap with the FMISO lesion and significant hypoperfusion, but only small overlap with the apparent diffusion coefficient lesion. Overlap of the T2' lesion regions of interest between the two raters was ∼50%. Conclusions This study provides formal validation of T2' to map non-core hypoxic tissue in acute stroke. T2' lesion delineation reproducibility was suboptimal, reflecting unclear lesion borders.

Impact of physiological noise correction on detecting blood oxygenation level-dependent contrast in the breast

Physiological fluctuations are expected to be a dominant source of noise in blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) experiments to assess tumour oxygenation and angiogenesis. This work investigates the impact of various physiological noise regressors: retrospective image correction (RETROICOR), heart rate (HR) and respiratory volume per unit time (RVT), on signal variance and the detection of BOLD contrast in the breast in response to a modulated respiratory stimulus. BOLD MRI was performed at 3 T in ten volunteers at rest and during cycles of oxygen and carbogen gas breathing. RETROICOR was optimized using F-tests to determine which cardiac and respiratory phase terms accounted for a significant amount of signal variance. A nested regression analysis was performed to assess the effect of RETROICOR, HR and RVT on the model fit residuals, temporal signal-to-noise ratio, and BOLD activation parameters. The optimized RETROICOR model accounted for the largest amount of signal variance ([Formula: see text]  =  3.3  ±  2.1%) and improved the detection of BOLD activation (P  =  0.002). Inclusion of HR and RVT regressors explained additional signal variance, but had a negative impact on activation parameter estimation (P  <  0.001). Fluctuations in HR and RVT appeared to be correlated with the stimulus and may contribute to apparent BOLD signal reactivity.

Targeted Molecular Imaging in Adrenal Disease-An Emerging Role for Metomidate PET-CT

Adrenal lesions present a significant diagnostic burden for both radiologists and endocrinologists, especially with the increasing number of adrenal ‘incidentalomas’ detected on modern computed tomography (CT) or magnetic resonance imaging (MRI). A key objective is the reliable distinction of benign disease from either primary adrenal malignancy (e.g., adrenocortical carcinoma or malignant forms of pheochromocytoma/paraganglioma (PPGL)) or metastases (e.g., bronchial, renal). Benign lesions may still be associated with adverse sequelae through autonomous hormone hypersecretion (e.g., primary aldosteronism, Cushing’s syndrome, phaeochromocytoma). Here, identifying a causative lesion, or lateralising the disease to a single adrenal gland, is key to effective management, as unilateral adrenalectomy may offer the potential for curing conditions that are typically associated with significant excess morbidity and mortality. This review considers the evolving role of positron emission tomography (PET) imaging in addressing the limitations of traditional cross-sectional imaging and adjunctive techniques, such as venous sampling, in the management of adrenal disorders. We review the development of targeted molecular imaging to the adrenocortical enzymes CYP11B1 and CYP11B2 with different radiolabeled metomidate compounds. Particular consideration is given to iodo-metomidate PET tracers for the diagnosis and management of adrenocortical carcinoma, and the increasingly recognized utility of ¹¹C-metomidate PET-CT in primary aldosteronism.

Detecting gas-induced vasomotor changes via blood oxygenation level-dependent contrast in healthy breast parenchyma and breast carcinoma

PURPOSE

To evaluate blood oxygenation level-dependent (BOLD) contrast changes in healthy breast parenchyma and breast carcinoma during administration of vasoactive gas stimuli.

MATERIALS AND METHODS

Magnetic resonance imaging (MRI) was performed at 3T in 19 healthy premenopausal female volunteers using a single-shot fast spin echo sequence to acquire dynamic T2 -weighted images. 2% (n = 9) and 5% (n = 10) carbogen gas mixtures were interleaved with either medical air or oxygen in 2-minute blocks, for four complete cycles. A 12-minute medical air breathing period was used to determine background physiological modulation. Pixel-wise correlation analysis was applied to evaluate response to the stimuli in breast parenchyma and these results were compared to the all-air control. The relative BOLD effect size was compared between two groups of volunteers scanned in different phases of the menstrual cycle. The optimal stimulus design was evaluated in five breast cancer patients.

RESULTS

Of the four stimulus combinations tested, oxygen vs. 5% carbogen produced a response that was significantly stronger (P < 0.05) than air-only breathing in volunteers. Subjects imaged during the follicular phase of their cycle when estrogen levels typically peak exhibited a significantly smaller BOLD response (P = 0.01). Results in malignant tissue were variable, with three out of five lesions exhibiting a diminished response to the gas stimulus.

CONCLUSION

Oxygen vs. 5% carbogen is the most robust stimulus for inducing BOLD contrast, consistent with the opposing vasomotor effects of these two gases. Measurements may be confounded by background physiological fluctuations and menstrual cycle changes. J. Magn. Reson. Imaging 2016;44:335-345.

Hypoxia and tissue destruction in pulmonary TB

Background

It is unknown whether lesions in human TB are hypoxic or whether this influences disease pathology. Human TB is characterised by extensive lung destruction driven by host matrix metalloproteinases (MMPs), particularly collagenases such as matrix metalloproteinase-1 (MMP-1).

Methods

We investigated tissue hypoxia in five patients with PET imaging using the tracer [¹⁸F]-fluoromisonidazole ([¹⁸F]FMISO) and by immunohistochemistry. We studied the regulation of MMP secretion in primary human cell culture model systems in normoxia, hypoxia, chemical hypoxia and by small interfering RNA (siRNA) inhibition.

Results

[¹⁸F]FMISO accumulated in regions of TB consolidation and around pulmonary cavities, demonstrating for the first time severe tissue hypoxia in man. Patlak analysis of dynamic PET data showed heterogeneous levels of hypoxia within and between patients. In Mycobacterium tuberculosis (M.tb)-infected human macrophages, hypoxia (1% pO₂) upregulated MMP-1 gene expression 170-fold, driving secretion and caseinolytic activity. Dimethyloxalyl glycine (DMOG), a small molecule inhibitor which stabilises the transcription factor hypoxia-inducible factor (HIF)-1α, similarly upregulated MMP-1. Hypoxia did not affect mycobacterial replication. Hypoxia increased MMP-1 expression in primary respiratory epithelial cells via intercellular networks regulated by TB. HIF-1α and NF-κB regulated increased MMP-1 activity in hypoxia. Furthermore, M.tb infection drove HIF-1α accumulation even in normoxia. In human TB lung biopsies, epithelioid macrophages and multinucleate giant cells express HIF-1α. HIF-1α blockade, including by targeted siRNA, inhibited TB-driven MMP-1 gene expression and secretion.

Conclusions

Human TB lesions are severely hypoxic and M.tb drives HIF-1α accumulation, synergistically increasing collagenase activity which will lead to lung destruction and cavitation.

Effect of Radiofrequency Transmit Field Correction on Quantitative Dynamic Contrast-enhanced MR Imaging of the Breast at 3.0 T

PURPOSE

To investigate the effects of radiofrequency transmit field (B1(+)) correction on (a) the measured T1 relaxation times of normal breast tissue and malignant lesions and (b) the pharmacokinetically derived parameters of malignant breast lesions at 3 T.

MATERIALS AND METHODS

Ethics approval and informed consent were obtained. Between May 2013 and January 2014, 30 women (median age, 58 years; range, 32-83 years) with invasive ductal carcinoma of at least 10 mm were recruited to undergo dynamic contrast material-enhanced magnetic resonance (MR) imaging before surgery. B1(+) and T1 mapping sequences were performed to determine the effect of B1(+) correction on the native tissue relaxation time (T10) of fat, parenchyma, and malignant lesions in both breasts. Pharmacokinetic parameters were calculated before and after correction for B1(+) variations. Results were correlated with histologic grade by using the Kruskal-Wallis test.

RESULTS

Measurements showed a mean 37% flip angle difference between the right and left breast, which resulted in a 61% T10 difference in fat and a 41.5% difference in parenchyma between the two breasts. The T1 of lesions in the right breast increased by 58%, whereas that of lesions in the left breast decreased by 30% after B1(+) correction. The whole-tumor transendothelial permeability across the vascular compartment(K(trans)) of lesions in the right breast decreased by 41%, and that of lesions in the left breast increased by 46% after correction. A systematic increase in K(trans) was observed, with significant differences found across the histologic grades (P < .001). The effect size of B1(+) correction on K(trans) calculation was large for lesions in the right breast and moderate for lesions in the left breast (Cohen effect size, d = 0.86 and d = 0.59, respectively).

CONCLUSION

B1(+) correction demonstrates a substantial effect on the results of quantitative dynamic contrast-enhanced analysis of breast tissue at 3 T, which propagates into the pharmacokinetic analysis of tumors that is dependent on whether the tumor is located in the right or left breast.

Imaging tumour hypoxia with positron emission tomography

Hypoxia, a hallmark of most solid tumours, is a negative prognostic factor due to its association with an aggressive tumour phenotype and therapeutic resistance. Given its prominent role in oncology, accurate detection of hypoxia is important, as it impacts on prognosis and could influence treatment planning. A variety of approaches have been explored over the years for detecting and monitoring changes in hypoxia in tumours, including biological markers and noninvasive imaging techniques. Positron emission tomography (PET) is the preferred method for imaging tumour hypoxia due to its high specificity and sensitivity to probe physiological processes in vivo, as well as the ability to provide information about intracellular oxygenation levels. This review provides an overview of imaging hypoxia with PET, with an emphasis on the advantages and limitations of the currently available hypoxia radiotracers.