[Positron emission tomography in oncology]

Positron emission tomography (PET) is a highly sensitive imaging tool that noninvasively characterizes metabolic processes and molecular targets. PET has become an integral part of oncological diagnostics and an increasingly important tool for oncological therapy management. PET assessment, for example, directly influences treatment escalation or de-escalation in context of Hodgkin lymphomas or is, in case of lung cancer, able to reduce unnecessary surgeries. Hence, molecular PET imaging represents an indispensable tool in the development of personalized treatments. Furthermore, the development of new radiotracers for specific cell surface structures offers a promising potential for diagnostics and-combined with therapeutic nuclides-also for therapies. One recent example are radioligands targeting prostate-specific membrane antigen, which are relevant in prostate cancer.

Molecular Imaging of Myocardial Fibroblast Activation in Patients with Advanced Aortic Stenosis Before Transcatheter Aortic Valve Replacement: A Pilot Study

Using multimodal imaging, we investigated the extent and functional correlates of myocardial fibroblast activation in patients with aortic stenosis (AS) scheduled for transcatheter aortic valve replacement (TAVR). AS may cause myocardial fibrosis, which is associated with disease progression and may limit response to TAVR. Novel radiopharmaceuticals identify upregulation of fibroblast activation protein (FAP) as a cellular substrate of cardiac profibrotic activity. Methods: Twenty-three AS patients underwent ⁶⁸Ga-FAP inhibitor 46 (⁶⁸Ga-FAPI) PET, cardiac MRI, and echocardiography within 1-3 d before TAVR. Imaging parameters were correlated and then were integrated with clinical and blood biomarkers. Control cohorts of subjects without a history of cardiac disease and with (n = 5) and without (n = 9) arterial hypertension were compared with matched AS subgroups. Results: Myocardial FAP volume varied significantly among AS subjects (range, 1.54-138 cm³, mean ± SD, 42.2 ± 35.6 cm³) and was significantly higher than in controls with (7.42 ± 8.56 cm³, P = 0.007) and without (2.90 ± 6.67 cm³; P < 0.001) hypertension. FAP volume correlated with N-terminal prohormone of brain natriuretic peptide (r = 0.58, P = 0.005), left ventricular ejection fraction (r = -0.58, P = 0.02), mass (r = 0.47, P = 0.03), and global longitudinal strain (r = 0.55, P = 0.01) but not with cardiac MRI T1 (spin-lattice relaxation time) and extracellular volume (P = not statistically significant). In-hospital improvement in left ventricular ejection fraction after TAVR correlated with pre-TAVR FAP volume (r = 0.440, P = 0.035), N-terminal prohormone of brain natriuretic peptide, and strain but not with other imaging parameters. Conclusion: FAP-targeted PET identifies varying degrees of left ventricular fibroblast activation in TAVR candidates with advanced AS. ⁶⁸Ga-FAPI signal does not match other imaging parameters, generating the hypothesis that it may become useful as a tool for personalized selection of optimal TAVR candidates.

Clinical Molecular Imaging of Pulmonary CXCR4 Expression to Predict Outcome of Pirfenidone Treatment in Idiopathic Pulmonary Fibrosis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a progressive disease for which two antifibrotic drugs recently were approved. However, an unmet need exists to predict responses to antifibrotic treatment, such as pirfenidone. Recent data suggest that upregulated expression of CXCR4 is indicative of outcomes in IPF.

RESEARCH QUESTION

Can quantitative, molecular imaging of pulmonary CXCR4 expression as a biomarker for disease activity predict response to the targeted treatment pirfenidone and prognosis in patients with IPF?

STUDY DESIGN AND METHODS

CXCR4 expression was analyzed by immunohistochemistry examination of lung tissues and reverse-transcriptase polymerase chain reaction analysis of BAL. PET-CT scanning with the specific CXCR4 ligand ⁶⁸Ga-pentixafor was performed in 28 IPF patients and compared with baseline clinical characteristics. In 16 patients, a follow-up scan was obtained 6 to 12 weeks after initiation of treatment with pirfenidone. Patients were followed up in our outpatient clinic for ≥ 12 months.

RESULTS

Immunohistochemistry analysis showed high CXCR4 staining of epithelial cells and macrophages in areas with vast fibrotic remodeling. Targeted PET scanning revealed CXCR4 upregulation in fibrotic areas of the lungs, particularly in zones with subpleural honeycombing. Baseline CXCR4 signal demonstrated a significant correlation with Gender Age Physiology stage (r = 0.44; P = .02) and with high-resolution CT scan score (r = 0.38; P = .04). Early changes in CXCR4 signal after initiation of pirfenidone treatment correlated with the long-term course of FVC after 12 months (r = -0.75; P = .0008). Moreover, patients with a high pulmonary CXCR4 signal on follow-up PET scan after 6 weeks into treatment demonstrated a statistically significant worse outcome at 12 months (P = .002). In multiple regression analysis, pulmonary CXCR4 signal on follow-up PET scan emerged as the only independent predictor of long-term outcome (P = .0226).

INTERPRETATION

CXCR4-targeted PET imaging identified disease activity and predicted outcome of IPF patients treated with pirfenidone. It may serve as a future biomarker for personalized guidance of antifibrotic treatment.

The Changing Face of Nuclear Cardiology: Guiding Cardiovascular Care Toward Molecular Medicine

Radionuclide imaging of myocardial perfusion, function, and viability has been established for decades and remains a robust, evidence-based and broadly available means for clinical workup and therapeutic guidance in ischemic heart disease. Yet, powerful alternative modalities have emerged for this purpose, and their growth has resulted in increasing competition. But the potential of the tracer principle goes beyond the assessment of physiology and function, toward the interrogation of biology and molecular pathways. This is a unique selling point of radionuclide imaging, which has been underrecognized in cardiovascular medicine until recently. Now, molecular imaging methods for the detection of myocardial infiltration, device infection, and cardiovascular inflammation are successfully gaining clinical acceptance. This is further strengthened by the symbiotic quest of cardiac imaging and therapy for an increasing implementation of molecule-targeted procedures, in which specific therapeutic interventions require specific diagnostic guidance toward the most suitable candidates. This review will summarize the current advent of clinical cardiovascular molecular imaging and highlight its transformative contribution to the evolution of cardiovascular therapy beyond mechanical interventions and broad blockbuster medication, toward a future of novel, individualized molecule-targeted and molecular imaging-guided therapies.

Beta-1-Adrenergic Receptor Antibodies in Acute Coronary Syndrome: Is Less Sometimes More?

Background: Anti-beta-1-adrenergic receptor antibodies (anti-β₁AR Ab) are associated with ischemic cardiomyopathies (ICM). Evidence continues to emerge supporting an autoimmune component to various cardiac diseases. This study compares anti-β₁AR Ab concentrations in patients with different entities of acute coronary syndromes (ACS) to asymptomatic non-ACS patients with positron-emission computed tomography (PET/CT)-proven atherosclerosis, and healthy controls.

Methods: Serum anti-β₁AR Ab IgG concentrations were measured in 212 ACS patients, 100 atherosclerosis patients, and 62 controls using ELISA. All ACS patients underwent coronary angiography. All 374 patients participating completed a structured questionnaire regarding traditional cardiovascular risk factors. ACS patients were followed up for 6 months.

Results: Patients with ACS exhibited lower anti-β₁AR Ab levels compared to patients with atherosclerosis or healthy controls (both p < 0.001). No differences in the ab levels were evident between healthy controls and patients with atherosclerosis. In the ACS groups, lower concentrations were found in patients with ST-elevation myocardial infarction (STEMI) (0.67 μg/ml) compared to patients with angina pectoris (AP) and non-ST elevation myocardial infarction (NSTEMI) (both 0.76 μg/ml, p = 0.008). Anti-β₁AR Ab levels ≤ 0.772 μg/ml were predictive for death and reinfarction (AUC 0.77, p = 0.006). No significant correlations between anti-β₁AR Ab levels and atherosclerotic burden or traditional cardiovascular risk factors were identified.

Conclusions: Lower anti-β₁AR Ab concentrations appear to characterize ACS phenotypes and could serve as diagnostic and prognostic markers independent from traditional risk factors for atheroscle. The prognostic predictive value of anti-β₁AR Ab in ACS remains to be confirmed in larger studies.

Participation of the spleen in the IgA immune response in the gut

The role of the spleen in the induction of an immune response to orally administered antigens is still under discussion. Although it is well known that after oral antigen administration specific germinal centres are not only formed in the Peyers patches (PP) and the mesenteric lymph nodes (mLN) but also in the spleen, there is still a lack of functional data showing a direct involvement of splenic B cells in an IgA immune response in the gut. In addition, after removal of mLN a high level of IgA+ B cells was observed in the gut. Therefore, in this study we analysed the role of the spleen in the induction of IgA+ B cells in the gut after mice were orally challenged with antigens. Here we have shown that antigen specific splenic IgM+ B cells after in vitro antigen stimulation as well as oral immunisation of donor mice were able to migrate into the gut of recipient mice, where they predominantly switch to IgA+ plasma cells. Furthermore, stimulation of recipient mice by orally administered antigens enhanced the migration of the splenic B cells into the gut as well as their switch to IgA+ plasma cells. Removal of the mLN led to a higher activation level of the splenic B cells. Altogether, our results imply that splenic IgM+ B cells migrate in the intestinal lamina propria, where they differentiate into IgA+ plasma cells and subsequently proliferate. In conclusion, we demonstrated that the spleen plays a major role in the gut immune response serving as a reservoir of immune cells that migrate to the site of antigen entrance.

Screening of extravascular findings in pulmonary embolism computer tomography: 397 patients with 1950 non-pulmonary artery findings

Objectives

The aim of this study was to investigate the possible benefits from computed tomography scans of patients with a suspected pulmonary artery embolism with a focus on relevant extravascular findings.

Methods

A total of 400 consecutive computed tomography pulmonary angiographies were evaluated. Computed tomography scans were analyzed in detail for the presence of pulmonary artery embolisms, as well as any other findings. Extra-artery discoveries were classified into none-relevant (Group A), intermediate (Group B), or relevant (Group C) findings.

Results

Aggregated computed tomography pulmonary angiographies detected other diagnosis than pulmonary artery embolism in 236 patients (59%). There were 1950 non-pulmonary artery embolism findings (4.9 per patient; n = 397). In the pulmonary artery embolism group, there were 447 extra-pulmonary artery embolism findings (5.2 per patient; n = 86) and in the non-pulmonary artery embolism group, 1503 findings (4.8 per patient; n = 311). Patients with pulmonary artery embolism had a significantly higher rate of pro-coagulate risk factors ( p < 0.001).

Conclusions

Computed tomography pulmonary angiographies may help to identify further diagnoses. This study represents a retrospective review of a single center experience for incidental computed tomography findings during pulmonary artery embolism work-up and emphasizes the importance of analyzing the whole field-of-view.

Extra-vascular findings in patients undergoing magnetic resonance angiography of the abdomen, pelvis and lower extremities: A retrospective study of 352 patients

Background

The aim of this study was to assess the prevalence and clinical significance of extra-vascular findings in patients undergoing magnetic resonance angiography of the abdomen, pelvis and lower extremities.

Materials and methods

Three hundred fifty-two patients underwent abdominal, pelvic and lower extremity 1.5 T magnetic resonance angiography. Clinically relevant vascular and extra-vascular findings were identified. Relevant vascular findings were classified as stenosis, occlusion, aneurysm, sclerosis, dissection or vasculitis. Relevant extra-vascular findings were categorized as ‘safe’ (Group A), intermediate – requiring additional investigation – (Group B) and malignant/endangering – requiring change of therapy (Group C).

Results

A total of 2152 clinically relevant vascular findings was identified (6.1/patient). The most frequent vascular finding was femoral artery stenosis (10.6%). Four hundred fifty-one extra-vascular findings were observed (1.3/patient) and classified into Group A (78%), Group B (19.5%) and Group C findings (2.4%). The most frequent malignant findings were lung cancer, lymphoma, osteosarcoma, hepatocellular carcinoma and renal cell carcinoma (7/352 patients).

Conclusions

Extravascular findings are frequently encountered in magnetic resonance angiography performed for vascular indications. Clinically relevant findings are seen in a substantial part of patients and should prompt further diagnostic work-up.

Incidental findings in cardiac magnetic resonance imaging: superiority of bSSFP over T1w-HASTE for extra-cardiac findings assessment

Incidental findings are frequent in radiological examinations and may have an impact on further patient management. The aim of this retrospective study was to analyze, which of two thoracic scout sequences is more suitable for detecting incidental extra-cardiac findings at cardiac magnetic resonance imaging (CMRI) with stress perfusion. During a 14-month period clinically indicated stress perfusion CMRI was performed in 97 consecutive patients. For anatomical orientation ECG-triggered (electrocardiography) T1w-Half-fourier acquisition single-shot turbo spin-echo (HASTE) and balanced steady state free precession (bSSFP) sequences were performed for planning the standard cardiac sequences. Two radiologists independently studied incidental extra-cardiac findings with both sequences and rated the diagnostic confidence of the sequences for this assessment using a multinomial model. Furthermore, the interobserver agreement between the observers was assessed by weighted kappa statistics. Eight patients without incidental findings were excluded. In the other 89 patients a total of 153 incidental extra-cardiac findings were observed. Overall, 47.1% of findings were seen with better diagnostic confidence at bSSFP as opposed to 20.6% at T1w-HASTE. 32.4% of findings were equally well seen with both sequences. Consequently the bSSFP sequence was significantly better in terms of diagnostic confidence for detecting the majority of extra-cardiac incidental findings (P < 0.01), whereas a minority of findings was better visible by the HASTE sequence. The weighted kappa statistics was 0.85, indicating good interobserver agreement. Compared with T1w-HASTE, the bSSFP sequence improved the visibility of incidental extra-cardiac findings at stress perfusion CMRI. While all findings were seen on both sequences, bSSFP resulted in improved diagnostic confidence, and the T1w-HASTE sequence provided complementary diagnostic information in only a minority of patients.

99mTc-HMPAO perfusion SPECT/CT in the diagnosis of brain death

This report describes a case of brain death (BD) evaluated by 99mTc-hexamethylpropylene amine oxime (HMPAO) single photon emission tomography/computed tomography (SPECT/CT). A 16-year-old boy with a history of rapid unexpected brain herniation due to pilocytic astrocytoma underwent 99mTc-HMPAO SPECT/CT for evaluation of brain death in the context of organ donation. Flow images demonstrated lack of blood flow to the brain, and delayed images showed absence of demonstrable radionuclide activity within the brain. SPECT/CT confirmed absence of tracer accumulation, and was deemed helpful for evaluation of the brain stem. 99mTc-HMPAO SPECT/CT is a valuable tool enabling imaging-based confirmation of BD.

Evaluation of 68 Ga-Glutamate Carboxypeptidase II Ligand Positron Emission Tomography for Clinical Molecular Imaging of Atherosclerotic Plaque Neovascularization

Objective—

Intraplaque neovascularization contributes to the progression and rupture of atherosclerotic lesions. Glutamate carboxypeptidase II (GCPII) is strongly expressed by endothelial cells of tumor neovasculature and plays a major role in hypoxia-induced neovascularization in rodent models of benign diseases. We hypothesized that GCPII expression may play a role in intraplaque neovascularization and may represent a target for imaging of atherosclerotic lesions. The aim of this study was to determine frequency, pattern, and clinical correlates of vessel wall uptake of a 68 Ga-GCPII ligand for positron emission tomographic imaging.

Approach and Results—

Data from 150 patients undergoing 68 Ga-GCPII ligand positron emission tomography were evaluated. Tracer uptake in various arterial segments was analyzed and was compared with calcified plaque burden, cardiovascular risk factors, and immunohistochemistry of carotid specimens. Focal arterial uptake of 68 Ga-GCPII ligand was identified at 5776 sites in 99.3% of patients. The prevalence of uptake sites was highest in the thoracic aorta; 18.4% of lesions with tracer uptake were colocalized with calcified plaque. High injected dose ( P =0.0005) and obesity ( P =0.007) were significantly associated with 68 Ga-GCPII ligand accumulation, but other cardiovascular risk factors showed no association. The number of 68 Ga-GCPII ligand uptake sites was significantly associated with overweight condition ( P =0.0154). Immunohistochemistry did not show GCPII expression. Autoradiographic blocking studies indicated nonspecific tracer binding.

Conclusions—

68 Ga-GCPII ligand positron emission tomography does not identify vascular lesions associated with atherosclerotic risk. Foci of tracer accumulation are likely caused by nonspecific tracer binding and are in part noise-related. Taken together, GCPII may not be a priority target for imaging of atherosclerotic lesions.