PET/CT and MR imaging in myeloma

Myeloma is the most common primary bone malignancy. It accounts for 10% of all hematological malignancies and 1% of all cancers. In the United States, there are an estimated 16,000 new cases and over 11,000 deaths yearly due to myeloma. Plasma cell dyscrasias manifest themselves in a variety of forms that range from MGUS (monoclonal gammopathy of undetermined significance) and smoldering myeloma that require no therapy, to the “malignant” form of multiple myeloma. The role of imaging in the management of myeloma includes: an assessment of the extent of intramedullary bone disease, detection of any extramedullary foci, and severity of the disease at presentation; the identification and characterization of complications; subsequent assessment of disease status. This review will focus on the use of PET/CT and MR imaging for myeloma patients at the time of initial diagnosis and for follow-up management, based on current reports in the literature and our practice at the Marlene and Stewart Greenebaum Cancer Center, University of Maryland Medical Center in Baltimore, USA.     

Integrated PET/MR

Integrated whole‐body PET/MR hybrid imaging combines excellent soft tissue contrast and various functional imaging parameters provided by MR with high sensitivity and quantification of radiotracer metabolism provided by positron emission tomography (PET). While clinical evaluation now is under way, integrated PET/MR demands for new technologies and innovative solutions, currently subject to interdisciplinary research. Attenuation correction of human soft tissues and of hardware components has to be MR‐based to maintain quantification of PET imaging because computed tomography (CT) attenuation information is missing. This brings up the question of how to provide bone information with MR imaging. The limited field‐of‐view in MR imaging leads to truncations in body imaging and MR‐based attenuation correction. Another research field is the implementation of motion correction technologies to correct for breathing and cardiac motion in view of the relatively long PET data acquisition times. Initial clinical applications of integrated PET/MR in oncology, neurology, pediatric oncology, and cardiovascular disease are highlighted. The hybrid imaging workflow here has to be tailored to the clinical indication to maximize diagnostic information while minimizing acquisition time. PET/MR introduces new artifacts that need special observation and innovative solutions for correction. Finally, the rising need for appropriate phantoms and standardization efforts in PET/MR hybrid imaging is discussed. J. Magn. Reson. Imaging 2014;39:243–258 . © 2013 Wiley Periodicals, Inc .     

Simultaneous PET/MR imaging in a human brain PET/MR system in 50 patients-Current state of image quality

Objectives

The present work illustrates the current state of image quality and diagnostic accuracy in a new hybrid BrainPET/MR.

Materials and methods

50 patients with intracranial masses, head and upper neck tumors or neurodegenerative diseases were examined with a hybrid BrainPET/MR consisting of a conventional 3T MR system and an MR-compatible PET insert. Directly before PET/MR, all patients underwent a PET/CT examination with either [¹⁸F]-FDG, [¹¹C]-methionine or [⁶⁸Ga]-DOTATOC. In addition to anatomical MR scans, functional sequences were performed including diffusion tensor imaging (DTI), arterial spin labeling (ASL) and proton-spectroscopy. Image quality score of MR imaging was evaluated using a 4-point-scale. PET data quality was assessed by evaluating FDG-uptake and tumor delineation with [¹¹C]-methionine and [⁶⁸Ga]-DOTATOC. FDG uptake quantification accuracy was evaluated by means of ROI analysis (right and left frontal and temporo-occipital lobes). The asymmetry indices and ratios between frontal and occipital ROIs were compared.

Results

In 45/50 patients, PET/MR examination was successful. Visual analysis revealed a diagnostic image quality of anatomical MR imaging (mean quality score T2 FSE: 1.27 ± 0.54; FLAIR: 1.38 ± 0.61). ASL and proton-spectroscopy was possible in all cases. In DTI, dental artifacts lead to one non-diagnostic dataset (mean quality score DTI: 1.32 ± 0.69; ASL: 1.10 ± 0.31). PET datasets of PET/MR and PET/CT offered comparable tumor delineation with [¹¹C]-methionine; additional lesions were found in 2/8 [⁶⁸Ga]-DOTATOC-PET in the PET/MR. Mean asymmetry index revealed a high accordance between PET/MR and PET/CT (1.5 ± 2.2% vs. 0.9 ± 3.6%; mean ratio (frontal/parieto-occipital) 0.93 ± 0.08 vs. 0.96 ± 0.05), respectively.

Conclusions

The hybrid BrainPET/MR allows for molecular, anatomical and functional imaging with uncompromised MR image quality and a high accordance of PET results between PET/MR and PET/CT. These results justify the application of this technique in further clinical studies and may contribute to the transfer into whole-body PET/MR systems.     

PET/CT在乳腺癌中的应用

乳腺癌是女性最常见的恶性肿瘤,如能得到早期诊断并早期治疗可明显地改善患者的预后情况甚至可以完全治愈。近年来正电子发射断层显像(PET)以及18F-FDG的广泛应用极大地改善了肿瘤患者的诊断和分期问题,及时改变了相应的治疗方法,而单纯的PET显像由于解剖定位欠清,有时正常生理性摄取与异常病理性摄取可能会难以鉴别,PET/CT的出现弥补了上述缺点,使FDGPET/CT在乳腺癌的分期与再分期、疗效监测、术前评估、原发病灶的诊断以及治疗方案的制订中都体现出自身独特的优势。     

Clinical evaluation of whole-body oncologic PET with time-of-flight and point-spread function for the hybrid PET/MR system

PurposeHybrid positron emission tomography/magnetic resonance (PET/MR) imaging is a new multimodality imaging technology that can provide structural and functional information simultaneously. The aim of this study was to investigate the effects of the time-of-flight (TOF) and point-spread function (PSF) on small lesions observed in PET/MR images from clinical patient image sets.Materials and methodsThis study evaluated 54 small lesions in 14 patients who had undergone ¹⁸F-fluorodeoxyglucose (FDG) PET/MR. Lesions up to 30 mm in diameter were included. The PET data were reconstructed with a baseline ordered-subsets expectation-maximization (OSEM) algorithm, OSEM + PSF, OSEM + TOF and OSEM + TOF + PSF. PET image quality and small lesions were visually evaluated and scored by a 3-point scale. A quantitative analysis was then performed using the mean and maximum standardized uptake value (SUV) of the small lesions (SUV_mean and SUV_max). The lesions were divided into two groups according to the long-axis diameter and the location respectively and evaluated with each reconstruction algorithm. We also evaluated the background signal by analyzing the SUV_liver.ResultsOSEM + TOF + PSF provided the highest value and OSEM + TOF or PSF showed a higher value than OSEM for the visual assessment and quantitative analysis. The combination of TOF and PSF increased the SUV_mean by 26.6% and the SUV_max by 30.0%. The SUV_liverwas not influenced by PSF or TOF. For the OSEM + TOF + PSF model, the change in SUV_mean and SUV_max for lesions <10 mm in diameter was 31.9% and 35.8%, and 24.5% and 27.6% for lesions 10–30 mm in diameter, respectively. The abdominal lesions obtained the higher SUV than those of chest on the images with TOF and/or PSF.ConclusionApplication of TOF and PSF significantly increased the SUV of small lesions in hybrid PET/MR images, potentially improving small lesion detectability.     

A comparative study: diffusion weighted whole body imaging with background body signal suppression and hybrid Positron Emission Computed Tomography on detecting lesions in oncologic clinics

Objective

To compare diffusion weighted whole body imaging with background body signal suppression (DWIBS) with hybrid Positron Emission Computed Tomography (HPET/CT) on clinical value in oncology.

Methods

43 patients with oncological diseases were enrolled in our hospital from October, 2008 to April, 2010. All the cases underwent DWIBS and HPET/CT within 14 days. Combined with other imagings, lesions detected by both modalities were evaluated. Lesions were confirmed by pathology, cytology or clinical diagnosis (needed no less than 6 months and three times follow-up).

Results

The overall detection rate of the DWIBS and HPET/CT were 90.3% (261/289), 86.6% (251/289), concordant ratio of the two modalities was 88.2% (255/289). There was no statistical difference between DWIBS and HPET/CT on detecting lesions (P > 0.05). HPET/CT was significantly more sensitive in detecting lesions in lung (P < 0.05), whereas DWIBS was more sensitive in identifying lesions in brain and bone (P < 0.05). With regard to finding lesions in liver and lymph node, the two procedures had no significant difference (P > 0.05).

Conclusion

DWIBS and HPET/CT have a certain degree of consistency in terms of identifying lesions. However, they have advantages and disadvantages in some organs or tissues, which should be taken into full consideration in clinical practice.     

Assessment of MR compatibility of a PET insert developed for simultaneous multiparametric PET/MR imaging on an animal system operating at 7 T

The combination of positron emission tomography and MR in one system is currently emerging and opens up new domains in the functional examinations of living systems. This article reports on relevant influences of a positron emission tomography insert on MR imaging. The basic conditions of main magnetic field and RF field homogeneity were measured as well as image quality and signal‐to‐noise ratio when applying the usual MR sequence types including echo‐planar techniques. Moreover, the influence of the positron emission tomography insert on the RF noise level and on RF interferences was measured by comparing results achieved with and without the positron emission tomography insert. The temporal stability of EPI imaging with and without the positron emission tomography insert was assessed. Small but significant decreases in the signal‐to‐noise ratio were revealed when the positron emission tomography insert was present, whereas B₀ and B₁ homogeneity as well as RF noise level were not adversely affected. A higher signal intensity drift was found for EPI imaging studies; however, this can be compensated by post processing. In summary, this study shows that positron emission tomography inserts can be designed for and used within an MR system practically, without substantially affecting the MR image quality. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.