PET-MRI Fusion in Head-and-Neck Oncology: Current Status and Implications for Hybrid PET/MRI

Positron Emission Tomography-Magnetic Resonance Imaging, a New Hybrid Imaging Modality for Dentomaxillofacial Malignancies-A Systematic Review

Background/Objectives: Emerging hybrid imaging modalities, like Positron Emission Tomography/Computed Tomography (PET/CT) and Positron Emission Tomography/Magnetic Resonance Imaging (PET/MRI), are useful for assessing head and neck cancer (HNC) and its prognosis during follow-up. PET/MRI systems enable simultaneous PET and MRI scans within a single session. These combined PET/MRI scanners merge MRI's better soft tissue contrast and the molecular metabolic information offered by PET. Aim: To review scientific articles on the use of hybrid PET/MRI techniques in diagnosing dentomaxillofacial malignancies. Method: The available literature on the use of PET/MRI for the diagnosis of dentomaxillofacial malignancies in four online databases (Scopus, PubMed, Web of Science, and the Cochrane Library) was searched. Eligible for this review were original full-text articles on PET/MRI imaging, published between January 2010 and November 2024, based on experimental or clinical research involving humans. Results: Out of the 783 articles retrieved, only twelve articles were included in this systematic review. Nearly half of the articles (5 out of 12) concluded that PET/MRI is superior to PET, MRI, and PET/CT imaging in relation to defining malignancies' size. Six articles found no statistically significant results and the diagnostic accuracy presented was similar in PET/MRI versus MRI and PET/CT images. Regarding the overall risk of bias, most articles had a moderate risk. Conclusions: The use of PET/MRI in HNC cases provides a more accurate diagnosis regarding dimensions of the tumor and thus a more accurate surgical approach if needed. Further prospective studies on a larger cohort of patients are required to obtain more accurate results on the application of hybrid PET/MRI.

Automatic autism spectrum disorder detection using artificial intelligence methods with MRI neuroimaging: A review

Autism spectrum disorder (ASD) is a brain condition characterized by diverse signs and symptoms that appear in early childhood. ASD is also associated with communication deficits and repetitive behavior in affected individuals. Various ASD detection methods have been developed, including neuroimaging modalities and psychological tests. Among these methods, magnetic resonance imaging (MRI) imaging modalities are of paramount importance to physicians. Clinicians rely on MRI modalities to diagnose ASD accurately. The MRI modalities are non-invasive methods that include functional (fMRI) and structural (sMRI) neuroimaging methods. However, diagnosing ASD with fMRI and sMRI for specialists is often laborious and time-consuming; therefore, several computer-aided design systems (CADS) based on artificial intelligence (AI) have been developed to assist specialist physicians. Conventional machine learning (ML) and deep learning (DL) are the most popular schemes of AI used for diagnosing ASD. This study aims to review the automated detection of ASD using AI. We review several CADS that have been developed using ML techniques for the automated diagnosis of ASD using MRI modalities. There has been very limited work on the use of DL techniques to develop automated diagnostic models for ASD. A summary of the studies developed using DL is provided in the Supplementary Appendix. Then, the challenges encountered during the automated diagnosis of ASD using MRI and AI techniques are described in detail. Additionally, a graphical comparison of studies using ML and DL to diagnose ASD automatically is discussed. We suggest future approaches to detecting ASDs using AI techniques and MRI neuroimaging.

Positron emission tomography and magnetic resonance imaging combined with computed tomography in tumor volume delineation: A case report

BACKGROUND

Accurate delineation of the target area for patients with hypopharyngeal cancer is the key to achieving an ideal radiotherapy effect. Since computed tomography (CT) alone can no longer meet the treatment needs, fusing CT images with magnetic resonance imaging (MRI) or positron emission tomography (PET) images can overcome the disadvantages of CT. Herein, we present a clinical case of hypopharyngeal cancer to delineate the tumor volume using combined MRI-CT and PET-CT fusion images to examine if they could accurately cover the tumor volume.

CASE SUMMARY

A 67-year-old male patient with hypopharyngeal carcinoma could not tolerate chemotherapy and surgery due to complicated health issues such as diabetic nephropathy and other underlying diseases. After multidisciplinary consultations, clinicians eventually agreed to undergo radiotherapy to control the progression of his tumor. He was examined by CT, MRI, and 18-fluorodeoxyglucose-PET for treatment planning, and CT images were fused with PET and MRI images while delineating tumor volume.

CONCLUSION

The image fusion of MRI-CT and PET-CT has both advantages and disadvantages. Compared with CT images alone, the combination of MRI-CT and PET-CT fusion images can precisely cover the gross tumor volume in hypopharyngeal carcinoma and avoid overestimation or incomplete coverage of tumor volume.

Advanced Magnetic Resonance Imaging of the Skull Base

Magnetic resonance (MR) imaging is a crucial tool for evaluation of the skull base, enabling characterization of complex anatomy by utilizing multiple image contrasts. Recent technical MR advances have greatly enhanced radiologists' capability to diagnose skull base pathology and help direct management. In this paper, we will summarize cutting-edge clinical and emerging research MR techniques for the skull base, including high-resolution, phase-contrast, diffusion, perfusion, vascular, zero echo-time, elastography, spectroscopy, chemical exchange saturation transfer, PET/MR, ultra-high-field, and 3D visualization. For each imaging technique, we provide a high-level summary of underlying technical principles accompanied by relevant literature review and clinical imaging examples.

Head–Neck Cancer Delineation

Head–Neck Cancer (HNC) has a relevant impact on the oncology patient population and for this reason, the present review is dedicated to this type of neoplastic disease. In particular, a collection of methods aimed at tumor delineation is presented, because this is a fundamental task to perform efficient radiotherapy. Such a segmentation task is often performed on uni-modal data (usually Positron Emission Tomography (PET)) even though multi-modal images are preferred (PET-Computerized Tomography (CT)/PET-Magnetic Resonance (MR)). Datasets can be private or freely provided by online repositories on the web. The adopted techniques can belong to the well-known image processing/computer-vision algorithms or the newest deep learning/artificial intelligence approaches. All these aspects are analyzed in the present review and comparison among various approaches is performed. From the present review, the authors draw the conclusion that despite the encouraging results of computerized approaches, their performance is far from handmade tumor delineation result.

Quantitative and qualitative evaluation of sequential PET/MRI using a newly developed mobile PET system for brain imaging

PURPOSE

To evaluate the clinical feasibility of a newly developed mobile PET system with MR-compatibility (flexible PET; fxPET), compared with conventional PET (cPET)/CT for brain imaging.

METHODS

Twenty-one patients underwent cPET/CT with subsequent fxPET/MRI using ¹⁸F-FDG. As qualitative evaluation, we visually rated image quality of MR and PET images using a four-point scoring system. We evaluated overall image quality for MR, while we evaluated overall image quality, sharpness and lesion contrast. As quantitative evaluation, we compared registration accuracy between two modalities [(fxPET and MRI) and (cPET and CT)] measuring spatial coordinates. We also examined the accuracy of regional ¹⁸F-FDG uptake.

RESULTS

All acquired images were of diagnostic quality and the number of detected lesions did not differ significantly between fxPET/MR and cPET/CT. Mean misregistration was significantly larger with fxPET/MRI than with cPET/CT. SUVmax and SUVmean for fxPET and cPET showed high correlations in the lesions (R = 0.84, 0.79; P < 0.001, P = 0.002, respectively). In normal structures, we also showed high correlations of SUVmax (R = 0.85, 0.87; P < 0.001, P < 0.001, respectively) and SUVmean (R = 0.83, 0.87; P < 0.001, P < 0.001, respectively) in bilateral caudate nuclei and a moderate correlation of SUVmax (R = 0.65) and SUVmean (R = 0.63) in vermis.

CONCLUSIONS

The fxPET/MRI system showed image quality within the diagnostic range, registration accuracy below 3 mm and regional ¹⁸F-FDG uptake highly correlated with that of cPET/CT.

Appropriate timing of surveillance intervals with whole-body 18F-FDG PET/CT following treatment for sinonasal malignancies

PURPOSE

To assess the ideal timing of posttreatment whole-body ¹⁸F-FDG PET/CT examination as routine surveillance to determine local recurrence (R), lymph node metastasis (LM), and distant metastasis (DM) of sinonasal malignancies and to investigate the effect of ¹⁸F-FDG PET/CT on survival.

METHODS

An overall 80 patients who had undergone a total of 197 posttreatment whole-body ¹⁸F-FDG PET/CT examinations for sinonasal malignancy were retrospectively examined after institutional review board approval. Patients were grouped regarding the time intervals (<1 month, 1-3 months, 3-6 months, 6-12 months, 12-18 months and >18 months) after the conclusion of treatment. Differences in diagnostic accuracy due to different follow-up intervals were calculated by receiver operator curves (ROC) and a Cox proportional hazards model was used to assess the prognostic value of surveillance ¹⁸F-FDG PET/CT.

RESULTS

Considering the time intervals of posttreatment ¹⁸F-FDG PET/CT scans, the negative predictive value and positive predictive value of the ¹⁸F-FDG PET/CT examinations to predict overall recurrence in 1-3 months (100 and 100%, respectively) and >18 months (100 and 95%, respectively) were higher than for recurrence detection in <1 month (50 and 100%, respectively), 3-6 months (81 and 93%, respectively), 6-12 months (79 and 87%, respectively), and 12-18 months (75 and 80%, respectively) (p < 0.05). Positive findings on ¹⁸F-FDG PET/CT scans were also independent predictors of poorer overall survival (OS) (p < 0.05).

CONCLUSIONS

Whole-body ¹⁸F-FDG PET/CT is capable of identifying recurrences following treatment, using an optimal time interval for scanning of 1-3 months and >18 months after therapy.

Functional MRI for Treatment Evaluation in Patients with Head and Neck Squamous Cell Carcinoma: A Review of the Literature from a Radiologist Perspective

PURPOSE OF REVIEW

To show the role of functional MRI in patients treated for head and neck squamous cell carcinoma.

RECENT FINDINGS

MRI is commonly used for treatment evaluation in patients with head and neck tumors. However, anatomical MRI has its limits in differentiating between post-treatment effects and tumor recurrence. Recent studies showed promising results of functional MRI for response evaluation.

SUMMARY

This review analyzes possibilities and limitations of functional MRI sequences separately to obtain insight in the post-therapy setting. Diffusion, perfusion and spectroscopy show promise, especially when utilized complimentary to each other. These functional MRI sequences aid in the early detection which might improve survival by increasing effectiveness of salvage therapy. Future multicenter longitudinal prospective studies are needed to provide standardized guidelines for the use of functional MRI in daily clinical practice.

Is integrated 18F-FDG PET/MRI superior to 18F-FDG PET/CT in the differentiation of incidental tracer uptake in the head and neck area?

PURPOSE

We aimed to investigate the accuracy of 18F-fluorodeoxyglucose positron emission tomography/magnetic resonance imaging (18F-FDG PET/MRI) compared with contrast-enhanced 18F-FDG PET/computed tomography (PET/CT) for the characterization of incidental tracer uptake in examinations of the head and neck.

METHODS

A retrospective analysis of 81 oncologic patients who underwent contrast-enhanced 18F-FDG PET/CT and subsequent PET/MRI was performed by two readers for incidental tracer uptake. In a consensus reading, discrepancies were resolved. Each finding was either characterized as most likely benign, most likely malignant, or indeterminate. Using all available clinical information including results from histopathologic sampling and follow-up examinations, an expert reader classified each finding as benign or malignant. McNemar's test was used to compare the performance of both imaging modalities in characterizing incidental tracer uptake.

RESULTS

Forty-six lesions were detected by both modalities. On PET/CT, 27 lesions were classified as most likely benign, one as most likely malignant, and 18 as indeterminate; on PET/MRI, 31 lesions were classified as most likely benign, one lesion as most likely malignant, and 14 as indeterminate. Forty-three lesions were benign and one lesion was malignant according to the reference standard. In two lesions, a definite diagnosis was not possible. McNemar's test detected no differences concerning the correct classification of incidental tracer uptake between PET/CT and PET/MRI (P = 0.125).

CONCLUSION

In examinations of the head and neck area, incidental tracer uptake cannot be classified more accurately by PET/MRI than by PET/CT.

An Evaluation of the Benefits of Simultaneous Acquisition on PET/MR Coregistration in Head/Neck Imaging

Coregistration of multimodal diagnostic images is crucial for qualitative and quantitative multiparametric analysis. While retrospective coregistration is computationally intense and could be inaccurate, hybrid PET/MR scanners allow acquiring implicitly coregistered images. Aim of this study is to assess the performance of state-of-the-art coregistration methods applied to PET and MR acquired as single modalities, comparing the results with the implicitly coregistration of a hybrid PET/MR, in complex anatomical regions such as head/neck (HN). A dataset consisting of PET/CT and PET/MR subsequently acquired in twenty-three patients was considered: performance of rigid (RR) and deformable (DR) registration obtained by a commercial software and an open-source registration package was evaluated. Registration accuracy was qualitatively assessed in terms of visual alignment of anatomical structures and qualitatively measured by the Dice scores computed on segmented tumors in PET and MRI. The resulting scores highlighted that hybrid PET/MR showed higher registration accuracy than retrospectively coregistered images, because of an overall misalignment after RR, unrealistic deformations and volume variations after DR. DR revealed superior performance compared to RR due to complex nonrigid movements of HN district. Moreover, simultaneous PET/MR offers unique datasets serving as ground truth for the improvement and validation of coregistration algorithms, if acquired with PET/CT.

Potential Role of PET/MRI for Imaging Metastatic Lymph Nodes in Head and Neck Cancer

OBJECTIVE

This article explores recent developments in PET and MRI, separately or combined, for assessing metastatic lymph nodes in patients with head and neck cancer.

CONCLUSION

The synergistic role of PET and MRI for imaging metastatic lymph nodes has not been fully explored. To facilitate the understanding of the areas that need further investigation, we discuss potential mechanisms and evidence reported so far, as well as future directions and challenges for continued development and clinical research.

Simultaneous (18)F-FDG-PET/MRI: Associations between diffusion, glucose metabolism and histopathological parameters in patients with head and neck squamous cell carcinoma

OBJECTIVES

To analyze possible associations between functional simultaneous (18)F-FDG-PET/MR imaging parameters and histopathological parameters in head and neck squamous cell carcinoma (HNSCC).

MATERIAL AND METHODS

11 patients (2 female, 9 male; mean age 56.0years) with biopsy-proven primary HNSCC underwent simultaneous (18)F-FDG-PET/MRI with a dedicated head and neck protocol including diffusion weighted imaging. For each tumor, glucose metabolism was estimated with standardized uptake values (SUV) and diffusion restriction was calculated using apparent diffusion coefficients (ADC). The tumor proliferation index was estimated on Ki 67 antigen stained specimens. Cell count, total nucleic area, and average nucleic area were estimated in each case. Pearson's correlation coefficient was used to analyze possible associations between the estimated parameters.

RESULTS

The mean SUVmax value was 24.41±6.51, and SUVmean value 15.01±4.07. Mean values (×10(-3)mm(2)s(-1)) of ADC parameters were as follows: ADCmin: 0.65±0.20; ADCmean: 1.28±0.18; and ADCmax: 2.16±0.35. Histopathological analysis identified the following results: cell count 1069.82±388.66, total nucleic area 150771.09±61177.12μm(2), average nucleic area 142.90±57.27μm(2) and proliferation index 49.09±22.67%. ADCmean correlated with Ki 67 level (r=-0.728, p=0.011) and total nucleic area (r=-0.691, p=0.019) and tended to correlate with average nucleic area (r=-0.527, p=0.096). ADCmax correlated with Ki 67 level (r=-0.633, p=0.036). SUVmax also tended to correlate with average nucleic area (r=0.573, p=0.066). Combined parameter SUVmax/ADCmin correlated with average nucleic area (r=0.627, p=0.039).

CONCLUSION

ADC and SUV values showed significant correlations with different histopathological parameters and can be used as biological markers in HNSCC.

Comparison of the Performances of (18)F-FP-CIT Brain PET/MR and Simultaneous PET/CT: a Preliminary Study

PURPOSE

(18)F-FP-CIT [(18)F-fluorinated N-3-fluoropropyl-2-beta-carboxymethoxy-3-beta-(4-iodophenyl) nortropane] has been well established and used for the differential diagnosis of atypical parkinsonian disorders. Recently, combined positron emission tomography (PET)/magnetic resonance (MR) was proposed as a viable alternative to PET/computed tomography (CT). The aim of this study was to compare the performances of conventional (18)F-FP-CIT brain PET/CT and simultaneous PET/MR by visual inspection and quantitative analysis.

METHODS

Fifteen consecutive patients clinically suspected of having Parkinson's disease were recruited for the study.(18)F-FP-CIT PET was performed during PET/CT and PET/MR. PET/CT image acquisition was started 90 min after intravenous injection of (18)F-FP-CIT and then PET/MR images were acquired. Dopamine transporter (DAT) density in bilateral striatal subregions was assessed visually. Quantitative analyses were performed on bilateral striatal volumes of interest (VOIs) using average standardized uptake values (SUVmeans). Intraclass correlation coefficients (ICCs) and their 95 % confidence intervals (CIs) were assessed to compare PET/CT and PET/MR data. Bland-Altman plots were drawn to perform method-comparisons.

RESULTS

All subjects showed a preferential decrease in DAT binding in the posterior putamen (PP), with relative sparing of the ventral putamen (VP). Bilateral striatal subregional binding ratio (BR) determined PET/CT and PET/MR demonstrated close interequipment correspondence (BRright caudate - ICC, 0.944; 95 % CI, 0.835-0.981, BRleft caudate - ICC, 0.917; 95 % CI, 0.753-0.972, BRright putamen - ICC, 0.976; 95 % CI, 0.929-0.992 and BRleft putamen - ICC, 0.970; 95 % CI, 0.911-0.990, respectively), and Bland-Altman plots showed interequipment agreement between the two modalities.

CONCLUSIONS

It is known that MR provides more information about anatomical changes associated with brain diseases and to enable the anatomical allocations of subregions than CT, though this was not observed in the present study. Although the subregional BR of simultaneous PET/MR was comparable to that of PET/CT in Parkinson's disease, our isocontouring method could make bias. A future automated method using standard template study or manual segmentation of putamen/caudate based on MR or CT is needed.

The value of imaging in subclinical coronary artery disease

Although the treatment of acute coronary syndromes (ACS) has advanced considerably, the ability to detect, predict, and prevent complications of atherosclerotic plaques, considered the main cause of ACS, remains elusive. Several imaging tools have therefore been developed to characterize morphological determinants of plaque vulnerability, defined as the propensity or probability of plaques to complicate with coronary thrombosis, able to predict patients at risk. By utilizing both intravascular and noninvasive imaging tools, indeed prospective longitudinal studies have recently provided considerable knowledge, increasing our understanding of determinants of plaque formation, progression, and instabilization. In the present review we aim at 1) critically analyzing the incremental utility of imaging tools over currently available "traditional" methods of risk stratification; 2) documenting the capacity of such modalities to monitor atherosclerosis progression and regression according to lifestyle modifications and targeted therapy; and 3) evaluating the potential clinical relevance of advanced imaging, testing whether detection of such lesions may guide therapeutic decisions and changes in treatment strategy. The current understanding of modes of progression of atherosclerotic vascular disease and the appropriate use of available diagnostic tools may already now gauge the selection of patients to be enrolled in primary and secondary prevention studies. Appropriate trials should now, however, evaluate the cost-effectiveness of an aggressive search of vulnerable plaques, favoring implementation of such diagnostic tools in daily practice.

Optimized imaging of the midface and orbits

A variety of imaging techniques are available for imaging the midface and orbits. This review article describes the different imaging techniques based on the recent literature and discusses their impact on clinical routine imaging. Imaging protocols are presented for different diseases and the different imaging modalities.

Imaging with (124)I in differentiated thyroid carcinoma: is PET/MRI superior to PET/CT?

PURPOSE

The aim of this study was to compare integrated PET/CT and PET/MRI for their usefulness in detecting and categorizing cervical iodine-positive lesions in patients with differentiated thyroid cancer using (124)I as tracer.

METHODS

The study group comprised 65 patients at high risk of iodine-positive metastasis who underwent PET/CT (low-dose CT scan, PET acquisition time 2 min; PET/CT2) followed by PET/MRI of the neck 24 h after (124)I administration. PET images from both modalities were analysed for the numbers of tracer-positive lesions. Two different acquisition times were used for the comparisons, one matching the PET/CT2 acquisition time (2 min, PET/MRI2) and the other covering the whole MRI scan time (30 min, PET/MRI30). Iodine-positive lesions were categorized as metastasis, thyroid remnant or inconclusive according to their location on the PET/CT images. Morphological information provided by MRI was considered for evaluation of lesions on PET/MRI and for volume information.

RESULTS

PET/MRI2 detected significantly more iodine-positive metastases and thyroid remnants than PET/CT2 (72 vs. 60, p = 0.002, and 100 vs. 80, p = 0.001, respectively), but the numbers of patients with at least one tumour lesion identified were not significantly different (21/65 vs. 17/65 patients). PET/MRI30 tended to detect more PET-positive metastases than PET/MRI2 (88 vs. 72), but the difference was not significant (p = 0.07). Of 21 lesions classified as inconclusive on PET/CT, 5 were assigned to metastasis or thyroid remnant when evaluated by PET/MRI. Volume information was available in 34 % of iodine-positive metastases and 2 % of thyroid remnants on PET/MRI.

CONCLUSIONS

PET/MRI of the neck was found to be superior to PET/CT in detecting iodine-positive lesions. This was attributed to the higher sensitivity of the PET component, Although helpful in some cases, we found no substantial advantage of PET/MRI over PET/CT in categorizing iodine-positive lesions as either metastasis or thyroid remnant. Volume information provided by MRI for some iodine-positive lesions might be useful in dosimetry.

In Vivo Correlation of Glucose Metabolism, Cell Density and Microcirculatory Parameters in Patients with Head and Neck Cancer: Initial Results Using Simultaneous PET/MRI

Objective

To demonstrate the feasibility of simultaneous acquisition of ¹⁸F-FDG-PET, diffusion-weighted imaging (DWI) and T1-weighted dynamic contrast-enhanced MRI (T1w-DCE) in an integrated simultaneous PET/MRI in patients with head and neck squamous cell cancer (HNSCC) and to investigate possible correlations between these parameters.

Methods

17 patients that had given informed consent (15 male, 2 female) with biopsy-proven HNSCC underwent simultaneous ¹⁸F-FDG-PET/MRI including DWI and T1w-DCE. SUV_max, SUV_mean, ADC_mean, ADC_min and K^trans, k_ep and v_e were measured for each tumour and correlated using Spearman’s ρ.

Results

Significant correlations were observed between SUV_mean and K^trans (ρ = 0.43; p ≤ 0.05); SUV_mean and k_ep (ρ = 0.44; p ≤ 0.05); K^trans and k_ep (ρ = 0.53; p ≤ 0.05); and between k_ep and v_e (ρ = -0.74; p ≤ 0.01). There was a trend towards statistical significance when correlating SUV_max and ADC_min (ρ = -0.35; p = 0.08); SUV_max and K^trans (ρ = 0.37; p = 0.07); SUV_max and k_ep (ρ = 0.39; p = 0.06); and ADC_mean and v_e (ρ = 0.4; p = 0.06).

Conclusion

Simultaneous ¹⁸F-FDG-PET/MRI including DWI and T1w-DCE in patients with HNSCC is feasible and allows depiction of complex interactions between glucose metabolism, microcirculatory parameters and cellular density.

Locoregional tumour evaluation of squamous cell carcinoma in the head and neck area: a comparison between MRI, PET/CT and integrated PET/MRI

PURPOSE

To evaluate the accuracy of integrated (18)F-FDG PET/MR imaging for locoregional tumour evaluation compared to (18)F-FDG PET/CT and MR imaging in initial tumour and recurrence diagnosis in histopathologically confirmed head and neck squamous cell carcinoma (HNSCC).

METHODS

(18)F-FDG PET/CT and integrated (18)F-FDG PET/MR imaging were performed for initial tumour staging or recurrence diagnosis in 25 patients with HNSCC. MR, fused (18)F-FDG PET/CT and fused (18)F-FDG PET/MR images were analysed by two independent readers in separate sessions in random order. In initial tumour staging, T and N staging was performed while individual lesions were analysed in patients with suspected cancer recurrence. In T and N staging, histopathological results after tumour resection served as the reference standard while histopathological sampling as well as cross-sectional and clinical follow-up were accepted in cancer recurrence diagnosis. The diagnostic accuracy of each modality was calculated separately for T and N staging as well as for tumour recurrence, and compared using McNemar's test. Values of p <0.017 were considered statistically significant after Bonferroni correction.

RESULTS

In 12 patients undergoing (18)F-FDG PET/CT and (18)F-FDG PET/MR for initial tumour staging, T staging was accurate in 50 % with MRI, in 59 % with PET/CT and in 75 % with PET/MR while N staging was accurate in 75 % with MRI, in 77 % with PET/CT and in 71 % with PET/MR in relation to the reference standard. No significant differences were observed in T and N staging among the three modalities (p > 0.017). In 13 patients undergoing hybrid imaging for cancer recurrence diagnosis, diagnostic accuracy was 57 % with MRI and in 72 % with (18)F-FDG PET/CT and (18)F-FDG PET/MR, respectively. Again, no significant differences were found among the three modalities (p > 0.017).

CONCLUSION

In this initial study, no significant differences were found among (18)F-FDG PET/MR, (18)F-FDG PET/CT and MRI in local tumour staging and cancer recurrence diagnosis.

k-space sampling optimization for ultrashort TE imaging of cortical bone: applications in radiation therapy planning and MR-based PET attenuation correction

PURPOSE

The ultrashort echo-time (UTE) sequence is a promising MR pulse sequence for imaging cortical bone which is otherwise difficult to image using conventional MR sequences and also poses strong attenuation for photons in radiation therapy and PET imaging. The authors report here a systematic characterization of cortical bone signal decay and a scanning time optimization strategy for the UTE sequence through k-space undersampling, which can result in up to a 75% reduction in acquisition time. Using the undersampled UTE imaging sequence, the authors also attempted to quantitatively investigate the MR properties of cortical bone in healthy volunteers, thus demonstrating the feasibility of using such a technique for generating bone-enhanced images which can be used for radiation therapy planning and attenuation correction with PET/MR.

METHODS

An angularly undersampled, radially encoded UTE sequence was used for scanning the brains of healthy volunteers. Quantitative MR characterization of tissue properties, including water fraction and R2(∗) = 1/T2(∗), was performed by analyzing the UTE images acquired at multiple echo times. The impact of different sampling rates was evaluated through systematic comparison of the MR image quality, bone-enhanced image quality, image noise, water fraction, and R2(∗) of cortical bone.

RESULTS

A reduced angular sampling rate of the UTE trajectory achieves acquisition durations in proportion to the sampling rate and in as short as 25% of the time required for full sampling using a standard Cartesian acquisition, while preserving unique MR contrast within the skull at the cost of a minimal increase in noise level. The R2(∗) of human skull was measured as 0.2-0.3 ms(-1) depending on the specific region, which is more than ten times greater than the R2(∗) of soft tissue. The water fraction in human skull was measured to be 60%-80%, which is significantly less than the >90% water fraction in brain. High-quality, bone-enhanced images can be generated using a reduced sampled UTE sequence with no visible compromise in image quality and they preserved bone-to-air contrast with as low as a 25% sampling rate.

CONCLUSIONS

This UTE strategy with angular undersampling preserves the image quality and contrast of cortical bone, while reducing the total scanning time by as much as 75%. The quantitative results of R2(∗) and the water fraction of skull based on Dixon analysis of UTE images acquired at multiple echo times provide guidance for the clinical adoption and further parameter optimization of the UTE sequence when used for radiation therapy and MR-based PET attenuation correction.

The added value of PET/Ce-CT/DW-MRI fusion in assessment of hepatic focal lesions: PET/Ce-CT/DW-MRI fusion in hepatic focal lesion

INTRODUCTION

The liver hosts a variety of benign and malignant tumors. Accurate diagnosis can be challenging in certain cases, especially in patients with a history of malignancy or in those with underlying liver pathology, such as cirrhosis.

OBJECTIVES

To evaluate the added clinical value of multi-modality liver imaging utilizing PET/Ce-CT/DW-MRI for characterization of hepatic focal lesions (HFL) and compare it with each diagnostic modality when interpreted alone.

METHODS

The study included 35 patients with HFL. They were 7 females & 28 males; their age ranged from 41 to 78years, all patients underwent PET/Ce-CT and DW-MRI scans. Ce-CT, PET and DW-MR images were reviewed independently, and then combined PET/Ce-CT, PET/DW-MRI and PET/Ce-CT/DW-MRI scans were analyzed. The results were correlated with histopathology or clinical/imaging follow-up.

RESULTS

The 35 patients had 98 focal lesions. Fifty-three lesions were finally diagnosed as primary hepatocellular carcinoma, 18 lesions were metastases, 7 lesions were lymphoma and 20 lesions were benign. On a patient based analysis; the sensitivity, specificity, PPV, NPV and accuracy were 100%, 67%, 94%, 100% and 94% for PET/Ce-CT compared to 97%, 83%, 97%, 83% and 94 % for DW-MRI, respectively. Combined PET/Ce-CT/DW-MR scans raise those parameters up to 100%. On a lesion based analysis; the sensitivity, specificity, PPV, NPV and accuracy were 94%, 75%, 94%, 75%, 90% for PET/Ce-CT compared to 94%, 95%, 99%, 97% and 94 % for DW-MRI, respectively. All these parameters were 100 % with PET/Ce-CT/DW-MRI.

CONCLUSIONS

The addition of DW-MRI to PET/Ce-CT is valuable in the characterization of hepatic focal lesions.

Diagnostic value of retrospective PET-MRI fusion in head-and-neck cancer

Background

To assess the diagnostic value of retrospective PET-MRI fusion and to compare the results with side-by-side analysis and single modality use of PET and of MRI alone for locoregional tumour and nodal staging of head-and-neck cancer.

Methods

Thirty-three patients with head-and-neck cancer underwent preoperative contrast-enhanced MRI and PET/CT for staging. The diagnostic data of MRI, PET, side-by-side analysis of MRI and PET images and retrospective PET-MRI fusion were systematically analysed for tumour and lymph node staging using receiver operating characteristic (ROC) analysis. The results were correlated to the histopathological evaluation.

Results

The overall sensitivity/specificity for tumour staging for MRI, PET, side-by-side analysis and retrospective PET-MRI fusion was 79%/66%, 82%/100%, 86%/100% and 89%/100%, respectively. The overall sensitivity/specificity for nodal staging on a patient basis for MRI, PET, side-by-side analysis and PET-MRI fusion was 94%/64%, 94%/91%, 94%/82% and 94%/82%, respectively. MRI, PET, side-by-side analysis and retrospective image fusion were associated with correct diagnosis/over-staging/under-staging of N-staging in 70.4%/18.5%/11.1%, 81.5%/7.4%/11.1%, 81.5%/11.1%/7.4% and 81.5%/11.1%/7.4%, respectively.

ROC analysis showed no significant differences in tumor detection between the investigated methods. The Area Under the Curve (AUC) for MRI, PET, side-by-side analysis and retrospective PET-MRI fusion were 0.667/0.667/0.702/0.708 (p > 0.05). The most reliable technique in detection of cervical lymph node metastases was PET imaging (AUC: 0.95), followed by side-by-side analysis and retrospective image fusion technique (AUC: 0.941), which however, was not significantly better then the MRI (AUC 0.935; p > 0.05).

Conclusions

We found a beneficial use of multimodal imaging, compared with MRI or PET imaging alone, particular in individual cases of recurrent tumour disease. Side-by-side analysis and retrospective image fusion analysis did not perform significantly differently.

Accuracy of (18)F-flurodeoxyglucose-positron emission tomography/computed tomography in the staging of newly diagnosed nasopharyngeal carcinoma: a systematic review and meta-analysis

Background

The specific role of 18F-flurodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) in staging of nasopharyngeal carcinoma (NPC) remains to be validated. A systematic review and meta-analysis were performed to assess the accuracy of staging FDG-PET/CT for newly diagnosed NPC.

Methods

We searched various biomedical databases and conference proceedings for relevant studies. We determined the pooled sensitivities and specificities, diagnostic odds ratios (DOR) and constructed summary receiver operating characteristic (SROC) curves using the hierarchical regression model.

Results

15 relevant studies including 851 patients were identified. Five addressed primary tumor (T), nine addressed regional lymph nodes (N) and seven addressed distant metastasis (M). The combined sensitivity estimate for FDG-PET/CT in T classification was 0.77 (95% confidence interval [CI] 0.59–0.95). For N classification, combined sensitivity was 0.84 (95% CI 0.76–0.91), specificity was 0.90 (95% CI 0.83–0.97), DOR was 82.4 (23.2–292.6) and Q*-index was 0.90. For M classification, the combined sensitivity estimate was 0.87 (95% CI 0.74–1.00), specificity was 0.98 (95% CI 0.96–1.00), DOR was 120.9 (43.0–340.0) and Q*-index was 0.89.

Conclusion

FDG-PET/CT showed good accuracy in N and M but not T classification for newly diagnosed NPC. FDG-PET/CT, together with Magnetic resonance imaging (MRI) of the nasopharynx, should be part of the routine staging investigations.

Molecular imaging of plaques in coronary arteries with PET and SPECT

Coronary artery disease remains a major cause of mortality. Presence of atherosclerotic plaques in the coronary artery is responsible for lumen stenosis which is often used as an indicator for determining the severity of coronary artery disease. However, the degree of coronary lumen stenosis is not often related to compromising myocardial blood flow, as most of the cardiac events that are caused by atherosclerotic plaques are the result of vulnerable plaques which are prone to rupture. Thus, identification of vulnerable plaques in coronary arteries has become increasingly important to assist identify patients with high cardiovascular risks. Molecular imaging with use of positron emission tomography (PET) and single photon emission computed tomography (SPECT) has fulfilled this goal by providing functional information about plaque activity which enables accurate assessment of plaque stability. This review article provides an overview of diagnostic applications of molecular imaging techniques in the detection of plaques in coronary arteries with PET and SPECT. New radiopharmaceuticals used in the molecular imaging of coronary plaques and diagnostic applications of integrated PET/CT and PET/MRI in coronary plaques are also discussed.

Does the novel integrated PET/MRI offer the same diagnostic performance as PET/CT for oncological indications?

BACKGROUND

We compared PET/MRI with PET/CT in terms of lesion detection and quantitative measurement to verify the feasibility of the novel integrated imaging modality for oncological applications.

METHODOLOGY/PRINCIPAL FINDINGS

In total, 285 patients referred to our PET/CT center for oncological indications voluntarily participated in this same-day PET/CT and PET/MRI comparative study. PET/CT images were acquired and reconstructed following routine protocols, and then PET/MRI was performed at a mean time interval of 28±11 min (range 15-45 min). PET/MRI covered the body trunk with a sequence combination of transverse T1WI 3D-volumetric interpolated breath-hold, T2WI turbo spin echo with fat saturation, diffusion-weighted imaging with double b values (50 and 800 s/mm2), and simultaneous PET acquisition over 45 min/5 bed positions. The maximum standardized uptake value (SUVmax) was assessed by manually drawn regions of interest over fluorodeoxyglucose-positive lesions. Among 285 cases, 57 showed no abnormalities, and 368 lesions (278 malignant, 68 benign and 22 undetermined) were detected in 228 patients. When stand-alone modalities were evaluated, PET revealed 31 and 12 lesions missed by CT and MRI, respectively, and CT and MRI revealed 38 and 61 more lesions, respectively, than PET. Compared to CT, MRI detected 40 more lesions and missed 8. In the integrated mode, PET/CT correctly detected 6 lesions misdiagnosed by PET/MRI, but was false-negative in 30 cases that were detected by PET/MRI. The overall diagnosis did not differ between integrated PET/MRI and PET/CT. SUVmax for lesions were slightly higher from PET/MRI than PET/CT but correlated well (ρ = 0.85-0.91).

CONCLUSIONS/SIGNIFICANCE

The novel integrated PET/MRI performed comparatively to PET/CT in lesion detection and quantitative measurements. PET from either scanner modality offered almost the same information despite differences in hardware. Further study is needed to explore features of integrated PET/MRI not addressed in this study.

Fluorodeoxyglucose positron emission tomography/magnetic resonance imaging: current status, future aspects

Simultaneous positron emission tomography (PET)/magnetic resonance (MR) imaging is a promising novel technology for oncology diagnosis and staging and neurologic and cardiac applications. Our institution's current research protocol results in a total imaging time of approximately 45 to 70 minutes with simultaneous PET/MR imaging, making this a feasible total body imaging protocol. Further development of MR-based attenuation correction will improve PET quantification. Quantitatively accurate multiparametric PET/MR data sets will likely improve diagnosis of disease and help guide and monitor the therapies for individualized patient care.

Positron emission tomography imaging of atherosclerosis

Atherosclerosis-related cardiovascular events are the leading causes of death in the industrialized world. Atherosclerosis develops insidiously and the initial manifestation is usually sudden cardiac death, stroke, or myocardial infarction. Molecular imaging is a valuable tool to identify the disease at an early stage before fatal manifestations occur. Among the various molecular imaging techniques, this review mainly focuses on positron emission tomography (PET) imaging of atherosclerosis. The targets and pathways that have been investigated to date for PET imaging of atherosclerosis include: glycolysis, cell membrane metabolism (phosphatidylcholine synthesis), integrin α_vβ_3, low density lipoprotein (LDL) receptors (LDLr), natriuretic peptide clearance receptors (NPCRs), fatty acid synthesis, vascular cell adhesion molecule-1 (VCAM-1), macrophages, platelets, etc. Many PET tracers have been investigated clinically for imaging of atherosclerosis. Early diagnosis of atherosclerotic lesions by PET imaging can help to prevent the premature death caused by atherosclerosis, and smooth translation of promising PET tracers into the clinic is critical to the benefit of patients.

Surfing the spectrum - what is on the horizon?

Diagnostic imaging techniques have evolved with technological advancements - but how far? The objective of this article was to explore the electromagnetic spectrum to find imaging techniques which may deliver diagnostic information of equal, or improved, standing to conventional radiographs and to explore any developments within radiography which may yield improved diagnostic data. A comprehensive literature search was performed using Medline, Web of Knowledge, Science Direct and PubMed Databases. Boolean Operators were used and key-terms included (not exclusively): terahertz, X-ray, ultraviolet, visible, infra-red, magnetic resonance, dental, diagnostic, caries and periodontal. Radiographic techniques are primarily used for diagnostic imaging in dentistry, and continued developments in X-ray imaging include: phase contrast, darkfield and spectral imaging. Other modalities have potential application, for example, terahertz, laser doppler and optical techniques, but require further development. In particular, infra-red imaging has regenerated interest with caries detection in vitro, due to improved quality and accessibility of cameras. Non-ionising imaging techniques, for example, infra-red, are becoming more commensurate with traditional radiographic techniques for caries detection. Nevertheless, X-rays continue to be the leading diagnostic image for dentists, with improved diagnostic potential for lower radiation dose becoming a reality.

Initial experience of MR/PET in a clinical cancer center

Magentic Resonance/positron emission tomography (PET) has been introduced recently for imaging of clinical patients. This hybrid imaging technology combines the inherent strengths of MRI with its high soft-tissue contrast and biological sequences with the inherent strengths of PET, enabling imaging of metabolism with a high sensitivity. In this article, we describe the initial experience of MR/PET in a clinical cancer center along with a review of the literature. For establishing MR/PET in a clinical setting, technical challenges, such as attenuation correction and organizational challenges, such as workflow and reimbursement, have to be overcome. The most promising initial results of MR/PET have been achieved in anatomical areas where high soft-tissue and contrast resolution is of benefit. Head and neck cancer and pelvic imaging are potential applications of this hybrid imaging technology. In the pediatric population, MR/PET can decrease the lifetime radiation dose. MR/PET protocols tailored to different types of malignancies need to be developed. After the initial exploration phase, large multicenter trials are warranted to determine clinical indications for this exciting hybrid imaging technology and thereby opening new horizons in molecular imaging.

Exploring temporospatial changes in glucose metabolic disorder, learning, and memory dysfunction in a rat model of diffuse axonal injury

Diffuse axonal injury (DAI) is the predominant effect of severe traumatic brain injury and contributes significantly to cognitive deficits. The mechanisms underlying these cognitive deficits are often associated with complex metabolic alterations. However, the relationships between temporospatial alterations in cerebral glucose metabolism and the pathophysiology of DAI-related learning and memory dysfunction are not yet completely understood. We used a small animal positron emission tomography (PET) scanner with 2-[F-18]-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) as a molecular probe to evaluate temporospatial glucose metabolism in vulnerable areas of rats with DAI. The Morris water maze (MWM) was used to evaluate the development and progression of learning and memory dysfunction. Compared to the sham-treated group, PET-MRI fusion images showed that glucose metabolism was reduced in animals with DAI. In addition, the standardized uptake value (SUV) of ¹⁸F-FDG was significantly decreased in the sensorimotor cortex, hippocampus, corpus callosum, caudate putamen, brain stem, and cerebellum at days 1, 3, and 7 after injury. SUV returned to baseline levels by 30 days after injury. The escape latency of the injured group was significantly increased, and the percentages of distance travelled and time spent in the target quadrant were significantly decreased 1 month after injury. These effects persisted for 3 months. SUVs in the hippocampus at the acute stage were significantly correlated with MWM performance during the recovery stage of DAI. These results demonstrate that microstructural injury-induced hypometabolism in the hippocampus at the acute stage are all significantly correlated with learning and memory dysfunctions during the recovery stage of DAI.

'Go with the flow ': a review of methods and advancements in blood flow imaging

Physics has delivered extraordinary developments in almost every facet of modern life. From the humble thermometer and stethoscope to X-Ray, CT, MRI, ultrasound, PET and radiotherapy, our health has been transformed by these advances yielding both morphological and functional metrics. Recently high resolution label-free imaging of the microcirculation at clinically relevant depths has become available in the research domain. In this paper, we present a comprehensive review on current imaging techniques, state-of-the-art advancements and applications, and general perspectives on the prospects for these modalities in the clinical realm.

MRI for attenuation correction in PET: methods and challenges

In current combined PET/MR systems, PET attenuation correction is based on MRI, since the small bore inside MRI systems and the strong magnetic field do not permit a rotating PET transmission source or a CT device to be integrated. Unlike CT measurements in PET/CT scanners, the MR signal is not directly correlated to tissue density and thus cannot be converted by a simple transformation of intensity values. Various approaches have been developed based on templates, atlas information, direct segmentation of T1-weighted MR images, or segmentation of images from special MR sequences. The advantages and disadvantages of these approaches as well as additional challenges will be discussed in this review.

Diagnostic value of combined ¹⁸F-FDG PET/MRI for staging and restaging in paediatric oncology

PURPOSE

The present study compares the diagnostic value of (18)F-fluorodeoxyglucose (FDG) positron emission tomography (PET) and MRI to combined/registered (18)F-FDG PET/MRI for staging and restaging in paediatric oncology.

METHODS

Over 8 years and 2 months, 270 (18)F-FDG PET and 270 MRI examinations (mean interval 5 days) were performed in 132 patients with proven (n = 117) or suspected (n = 15) malignant disease: solid tumours (n = 64), systemic malignancy (n = 53) and benign disease (n = 15). A total of 259 suspected tumour lesions were analysed retrospectively during primary diagnosis and 554 lesions during follow-up. Image analysis was performed separately on each modality, followed by analysis of combined and registered (18)F-FDG PET/MRI imaging.

RESULTS

A total of 813 lesions were evaluated and confirmed by histopathology (n = 158) and/or imaging follow-up (n = 655) after 6 months. In the separate analysis of (18)F-FDG PET and MRI, sensitivity was 86 %/94 % and specificity 85 %/38 %. Combined/registered (18)F-FDG PET/MRI led to a sensitivity of 97 %/97 % and specificity of 81 %/82 %. False-positive results ((18)F-FDG PET n = 69, MRI n = 281, combined (18)F-FDG PET/MRI n = 85, registered (18)F-FDG PET/MRI n = 80) were due to physiological uptake or post-therapeutic changes. False-negative results ((18)F-FDG PET n = 50, MRI n = 20, combined (18)F-FDG PET/MRI n = 11, registered (18)F-FDG PET/MRI n = 11) were based on low uptake or minimal morphological changes. Examination-based evaluation during follow-up showed a sensitivity/specificity of 91 %/81 % for (18)F-FDG PET, 93 %/30 % for MRI and 96 %/72 % for combined (18)F-FDG PET/MRI.

CONCLUSION

For the detection of single tumour lesions, registered (18)F-FDG PET/MRI proved to be the methodology of choice for adequate tumour staging. In the examination-based evaluation, MRI alone performed better than (18)F-FDG PET and combined/registered imaging during primary diagnosis. At follow-up, however, the examination-based evaluation demonstrated a superiority of (18)F-FDG PET alone.

First clinical experience with integrated whole-body PET/MR: comparison to PET/CT in patients with oncologic diagnoses

The recently introduced first integrated whole-body PET/MR scanner allows simultaneous acquisition of PET and MRI data in humans and, thus, may offer new opportunities, particularly regarding diagnostics in oncology. This scanner features major technologic differences from conventional PET/CT devices, including the replacement of photomultipliers with avalanche photodiodes and the need for MRI-based attenuation correction. The aim of this study was to evaluate the comparability of clinical performance between conventional PET/CT and PET/MR in patients with oncologic diseases.

METHODS

Thirty-two patients with different oncologic diagnoses underwent a single-injection, dual-imaging protocol consisting of a PET/CT and subsequent PET/MR scan. PET/CT scans were performed according to standard clinical protocols (86 ± 8 min after injection of 401 ± 42 MBq of (18)F-FDG, 2 min/bed position). Subsequently (140 ± 24 min after injection), PET/MR was performed (4 min/bed position). PET images of both modalities were reconstructed iteratively. Attenuation and scatter correction as well as regional allocation of PET findings were performed using low-dose CT data for PET/CT and Dixon MRI sequences for PET/MR. PET/MR and PET/CT were compared visually by 2 teams of observers by rating the number and location of lesions suspicious for malignancy, as well as image quality and alignment. For quantitative comparison, standardized uptake values (SUVs) of the detected lesions and of different tissue types were assessed.

RESULTS

Simultaneous PET/MR acquisition was feasible with high quality in short acquisition time (≤ 20 min). No significant difference was found between the numbers of suspicious lesions (n = 80) or lesion-positive patients (n = 20) detected with PET/MR or PET/CT. Anatomic allocation of PET/MR findings by means of the Dixon MRI sequence was comparable to allocation of PET/CT findings by means of low-dose CT. Quantitative evaluation revealed a high correlation between mean SUVs measured with PET/MR and PET/CT in lesions (ρ = 0.93) and background tissue (ρ = 0.92).

CONCLUSION

This study demonstrates, for what is to our knowledge the first time, that integrated whole-body PET/MR is feasible in a clinical setting with high quality and in a short examination time. The reliability of PET/MR was comparable to that of PET/CT in allowing the detection of hypermetabolic lesions suspicious for malignancy in patients with oncologic diagnoses. Despite different attenuation correction approaches, tracer uptake in lesions and background correlated well between PET/MR and PET/CT. The Dixon MRI sequences acquired for attenuation correction were found useful for anatomic allocation of PET findings obtained by PET/MR in the entire body. These encouraging results may form the foundation for future studies aiming to define the added value of PET/MR over PET/CT.