Integrating imaging modalities: what makes sense from a workflow perspective?

Purpose: From a workflow/cost perspective integrated imaging is not an obvious solution. An analysis of scanning costs as a function of system cost and relevant imaging times is presented. This analysis ignores potential clinical advantages of integrated imaging. Methods: An analysis comparing separate vs integrated imaging costs was performed by deriving pertinent equations and using reasonable cost numbers for imaging devices and systems, room and other variable costs. Integrated systems were divided into those sequentially and simultaneously. Sequential scanning can be done with two devices placed in a single or in two different scanning rooms. Graphs were derived which represent the cost difference between integrated imaging system options and their separate counterparts vs scanning time on one of the devices and cost ratio of an integrated system and its counterpart of separate devices. Results: Integrated systems are favoured by the fact that patients have to be up- and downloaded only once. If imaging times become longer than patient changing times, imaging on separate devices is advantageous. An integrated imaging cost advantage is achieved if the integrated systems typically and overall cost three fourths or less of the separate systems. If PET imaging takes 15 min or less, PET/CT imaging costs less than separate PET and CT imaging, while this time is below 5min for SPECT/CT. A two-room integrated system has the added advantage that patient download time is not cost relevant, when imaging times on the two devices differ by more than the patient download time. Conclusion: PET/CT scanning is a cost-effective implementation of an integrated system unlike most current SPECT/CT systems. Integration of two devices in two rooms by a shuttle seems the way how to make PET/MR cost-effective and may well also be a design option for SPECT/CT system

A look ahead: PET/MR versus PET/CT

Introduction: Integration of positron emission tomography (PET) and magnetic resonance (MR) has become a topic of increasing interest to the imaging community over the past two years. Objectives: In this text, the authors attempt to distinguish facts from fiction concerning such integrated systems. Analysis of existing information of combined imaging on existing brain PET/MR systems and imaging experience with PET-computed tomography (CT) is reviewed. Various types of system integration of PET and MR are discussed with completely independent systems on one hand and completely integrated systems with the possibility of simultaneous data acquisition on the other hand. Furthermore, it is discussed, what simultaneous data acquisition with nuclear imaging systems combined with MR or CT really means, as technical simultaneity may not be relevant in light of the pharmacokinetics of the nuclear tracers used. Discussion: The authors conclude that combining PET/MR is an interesting research endeavor with uncertain outcome. They argue that, while completely simultaneous brain applications are of research interest immediately, clinical applications do not currently warrant the construction of fully integrated systems. Systems adjacent to each other, where imaging tables are linked with a patient "shuttle” thereby requiring only patient translation but no repositioning, may be a good start to assess the value of integrated PET/M

Iatrogenic FDG foci in the lungs: a pitfall of PET image interpretation

Abstract.: 2-[F-18]-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) has become an important staging modality for many tumors, including bronchial carcinoma; however it is important to know that there are several pitfalls in PET image interpretation. In this report we demonstrate three cases in which focal intrapulmonary FDG uptake could possibly represent iatrogenic microembolism. These FDG accumulations would have been interpreted as malignant tumor mass in the lung if no anatomic correlation would have been performed. For this reason, we further present an integrated PET/CT scanner, which recently has been introduced. This correlation of molecular and morphological information enables the specification of the FDG-PET finding

FDG PET and PET/CT for the detection of the primary tumour in patients with cervical non-squamous cell carcinoma metastasis of an unknown primary

In patients with a neck metastasis from an unknown primary with non-squamous cell cancer (non-SCC) histology, the primary is often located outside the head and neck area. We retrospectively evaluated 326 patient records and found 14 patients with non-SCC neck lymph node metastasis from an unknown primary undergoing whole body F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET) with or without coregistered computed tomography (PET/CT). The PET or PET/CT findings were verified by pathological work-up, additional imaging tests, and clinical follow-up. PET detected pathological FDG uptake suspicious for the primary in eight patients. PET or PET/CT findings were true positive in seven patients, true negative in 4, false positive in 1, and false negative in two patients. In one patient PET/CT revealed a synchronous ovarian carcinoma. The results suggest that whole body imaging with FDG PET and PET/CT can be useful to identify unknown primaries of non-SCC origin. However, the work-up of patients undergoing PET or PET/CT in our study was very heterogeneous and the primary was more likely found in patients without extensive imaging before PET scanning. Further studies should evaluate if the histology of a neck nodal metastasis should influence the choice of the imaging method and the role of PET and PET/CT imaging for the work up of patients with a non-SCC neck lymph node metastasis of an unknown primar

PET-MR imaging using a tri-modality PET/CT-MR system with a dedicated shuttle in clinical routine

Tri-modality PET/CT-MRI includes the transfer of the patient on a dedicated shuttle from one system into the other. Advantages of this system include a true CT-based attenuation correction, reliable PET-quantification and higher flexibility in patient throughput on both systems. Comparative studies of PET/MRI versus PET/CT are readily accomplished without repeated PET with a different PET scanner at a different time point. Additionally, there is a higher imaging flexibility based on the availability of three imaging modalities, which can be combined for the characterization of the disease. The downside is a somewhat higher radiation dose of up to 3mSv with a low dose CT based on the CT-component, longer acquisition times and potential misalignment between the imaging components. Overall, the tri-modality PET/CT-MR system offers comparative studies using the three different imaging modalities in the same patient virtually at the same time, and may help to develop reliable attenuation algorithms at the same tim

Clinical evaluation of a breathing protocol for PET/CT

The aim of this study was to assess the frequency and severity of respiration-induced curvilinear respiration artifacts (RICA) on co-registered positron emission tomography/computed tomography (PET/CT) images acquired on a combined PET/CT scanner before and after modifying the respiration protocol for CT scanning, with retrospective analysis of two groups of 100 patients each, before and after implementing a respiration protocol with breath-hold (BH) in the normal expiration position for the acquisition of the CT images. The CT data were used as attenuation map and for image co-registration. A ranking of co-registered PET/CT and PET images (including maximum intensity projection) was done by two observers in consensus using a scale from 0 to 3. Zero indicated that no RICA was visible and 1, 2, and 3 described artifact with increasing severity. A significant difference in RICA occurrence was found between the two groups (p<0.0001). There was a 45% decrease of artifact frequency when using the normal expiration protocol and a 68% decrease of grade-2 and grade-3 artifacts (p=0.004). The results of this study suggest that BH during the normal expiration position for CT scanning can be recommended to reduce the occurrence and the severity of RICA on PET/C