Felipe Godinez

High-resolution 18F-FDG PET with MRI for monitoring response to treatment in rheumatoid arthritis

Eur J Nucl Med Mol Imaging (2010) 37:1047 DOI 10.1007/s00259-009-1364-x IMAGE OF THE MONTH High-resolution 18 F-FDG PET with MRI for monitoring response to treatment in rheumatoid arthritis Abhijit J. Chaudhari & Spencer L. Bowen & George W. Burkett & Nathan J. Packard & Felipe Godinez & Anand A. Joshi & Stanley M. Naguwa & David K. Shelton & John C. Hunter & John M. Boone & Michael H. Buonocore & Ramsey D. Badawi Received: 20 November 2009 / Accepted: 10 December 2009 / Published online: 30 January 2010 # The Author(s) 2010. This article is published with open access at Springerlink.com Molecular imaging can potentially provide means for mon- itoring response to therapy in rheumatoid arthritis (RA) early in the course of disease [1].Quantitative measurements of RA disease activity made in the wrist by whole-body PET scanners, however, have inadequate accuracy because of limited spatial resolution [2]. A high-resolution PET/CT scanner for imaging extremities has been built at our insti- tution [3]. In conjunction with a clinical MRI scanner, high- resolution PET/MR images can be obtained for the wrist. The CT image is used for PET/MR image coregistration. A 57-year-old female with established RA was stable until a recent clinical flare-up in the right wrist. Clinical exami- nation revealed synovitis, swelling, and diminished range of motion. The patient also had a history of osteoarthritis (OA). An extremity 18 F-FDG PET/CT scan immediately following MRI at baseline was performed on this patient. Tumor necrosis factor alpha (TNF-α) inhibitor (etanercept) therapy was then initiated as a part of the patient’s standard of care. The patient was re-scanned 5 weeks after starting treatment. The figure shows high-resolution 18 F-FDG PET images (pseudocolor) overlaid on pre-contrast MRI images (gray This work was funded by the NIH grants UL1-RR024146, R01CA129561, R01EB002138 and the UC Davis Imaging Research Center. A. J. Chaudhari (*) : S. L. Bowen : G. W. Burkett : N. J. Packard : F. Godinez : D. K. Shelton : J. C. Hunter : J. M. Boone : M. H. Buonocore : R. D. Badawi Department of Radiology, UC Davis Medical Center, Sacramento, CA, USA e-mail: ajchaudhari@ucdavis.edu A. A. Joshi Department of Neurology, UCLA School of Medicine, Los Angeles, CA, USA S. M. Naguwa Department of Internal Medicine, UC Davis Medical Center, Sacramento, CA, USA scale) at baseline (left column) and 5 weeks (right column). Significant reduction in PET signal (suggesting reduced inflammation) in the synovium and at sites of erosions (white arrows) is visible. The green arrow shows inflammation due to OA. Physician examination at 3 months confirmed that this patient responded positively to etanercept. This case illustrates the potential of high-resolution PET with MRI for quantitative visualization of early response to therapy in RA. Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which per- mits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References 1. Brenner W. 18F-FDG PET in rheumatoid arthritis: there still is a long way to go. J Nucl Med. 2004;45(6):927–9. 2. Beckers C, Ribbens C, Andre B, Marcelis S, Kaye O, Mathy L, et al. Assessment of disease activity in rheumatoid arthritis with (18)F-FDG PET. J Nucl Med. 2004;45(6):956–64. 3. Bowen SL, Wu Y, Chaudhari AJ, Fu L, Packard NJ, Burkett GW, et al. Initial characterization of a dedicated breast PET/CT scanner during human imaging. J Nucl Med. 2009;50(9):1401–8.

High-resolution 18F-FDG PET/CT for assessing disease activity in rheumatoid and psoriatic arthritis: findings of a prospective pilot study

OBJECTIVE Rheumatoid arthritis (RA) and psoriatic arthritis (PsA) commonly affect the small joints of the wrist and hand. We evaluated the performance of a new, high-resolution extremity positron emission tomography (PET)/CT scanner for characterizing and quantifying pathologies associated with the two arthritides in the wrist and hand joints. METHODS Patients with RA or PsA underwent fluorine-18 fludeoxyglucose ((18)F-FDG) PET/CT wrist and hand imaging, respectively, on the high-resolution scanner. Calibrated CT images and co-registered PET images were reconstructed. PET/CT was derived for the radiocarpal and pisiform-triquetral compartments, joints with erosive changes, sites of synovitis or tenosynovitis and the nail bed and were correlated with clinical and MRI findings. RESULTS Significantly elevated (18)F-FDG uptake was measured for the radiocarpal and pisiform-triquetral compartments and at sites of bone erosion, synovitis, pannus and oedema, compared with unaffected joints (p < 0.05) in patients with RA, consistent with their clinical findings. In patients with PsA, significantly elevated (18)F-FDG uptake was measured for joints with synovitis compared with unaffected joints (p < 0.05), with patterns of (18)F-FDG uptake along the tendons, at the enthesis and in the nail bed, consistent with tenosynovitis, enthesitis and nail dystrophy, respectively. CONCLUSION High-resolution (18)F-FDG PET/CT imaging of the wrist and hand is feasible in an RA or PsA patient cohort and is capable of providing quantifiable measures of disease activity (synovitis, enthesitis, oedema and bone destruction). ADVANCES IN KNOWLEDGE High-resolution PET/CT imaging shows promise as a tool for understanding the pathogenesis of the arthritic process and for non-invasive, objective assessment of RA or PsA severity and therapy selection.

A prototype PET scanner with hybrid DOI-encoding detectors

POSITRON emission tomography (PET) is used in assessing therapy response, staging, and restaging of breast cancer [1]. However, whole-body PET scanners are not ideally suited to breast imaging due to low geometric sensitivity, low spatial resolution and signal loss due to attenuation in the body. Several groups are working on dedicated breast imaging systems to overcome such limitations[2][3]. Due to the typically smaller field of view (FOV), detectors capable of measuring depth of interaction (DOI) can yield better performance in dedicated breast PET scanners. A high resolution positron emission tomography/computed tomography (PET/CT) scanner that uses DOI encoding detectors and is dedicated for human breast imaging is currently been developed in our laboratory. This paper presents the design and implementation of a prototype of the PET component of the aforementioned scanner.

A modular hybrid PSPMT/SiPM depth encoding detector for high resolution positron emission tomography

PERFORMANCE of positron emission tomography (PET) scanners can be improved by using detectors that can measure depth of interaction (DOI) [1]. Dual ended readout is one of the widely studied methods to measure DOI. In this design two photodetectors are coupled to either end of a crystal or a block of crystals and DOI is estimated using the ratio of signal amplitudes recorded by the two photodetectors [2][3][4][5][6]. A hybrid dual ended readout DOI detector that uses a position sensitive photomultiplier tube (PSPMT) and an Avalanche photo diode (APD) for photodetection was presented in [2]. This prototype was further developed into a modular detector that encapsulates the electronic and mechanical functionality of a gamma detector to a compact self contained unit [7]. The modular detector can be easily integrated into new scanner designs with no changes to the detector itself. This facilitates rapid and cost effective development of application specific PET scanners. Such modules may also be rapidly transferred from one scanner gantry to another. The APD used in [7] requires a bias voltage of over 1800 V. The signal produced by APD is orders of magnitude smaller compared to PSPMT signal and requires extremely high amplification. Moreover, APD signal has to be routed near the body of the PSPMT. Therefore, shielding is required to reduce the interference from PSPMT. To address these shortcoming a modular detector was designed using SiPMs instead of APDs. SiPMs used in this detector requires bias voltages in the range 26V-29.5V and requires simpler amplifier circuitry due to the stronger signals produced.

Design and initial performance evaluation of DbPET2, an intermediate generation breast PET prototype

The combined effort of several laboratories at our institution resulted in the building of the first dedicated, breast PET/CT prototype. Ongoing clinical trials for breast cancer diagnosis and assessment of response to treatment underlined the need of a second generation prototype with improved sensitivity and spatial resolution. The goals of the new prototype are to reduce scan time and partial volume effects on quantitative measurements of small lesions. Several designs have been proposed by our group and are currently under investigation at different levels. In this work, we present the complete characterization of a detector module for an intermediate generation breast PET prototype, together with its design and assembly. The proposed design consists of two heads, shaped around the circumference of a circle of radius 26 cm. Each head is formed by 2 rows of 8 modules each, each module consisting in a 14×14 array of unpolished LSO crystals, read out by a position sensitive photomultiplier tube (PSPMT). Crystal pitch is 1.5 mm. A complete characterization of two detectors modules in coincidence resulted in an energy resolution of 25.2%, a timing resolution of 2.4 ns and an average intrinsic spatial resolution for a central row in the array of 1.26 mm. The two detector heads are now fully assembled and connected to the electronics suite for data processing. Modification of the system electronics is underways and the first floods, showing excellent position encoding, are presented. A thorough evaluation of system performance will be completed in the next few months. We plan to combine this scanner with a third generation breast CT system currently under parallel development to form a new generation, dedicated breast PET/CT scanner.