Integrated PET-CT improves the diagnostic accuracy of the staging of non-small-cell lung cancer.

Increased symmetrical fluorine-18 fluorodeoxyglucose (FDG) uptake in the cervical and thoracic spine region is well known and has been attributed to muscular uptake. The purpose of this study was to re-evaluate this FDG uptake pattern by means of co-registered positron emission tomography (PET) and computed tomography (CT) imaging, which allowed exact localisation of this uptake. Between April and November 2001, 638 consecutive patients referred for PET/CT were imaged on an in-line PET/CT system (GEMS). This system combines an advanced GE PET scanner and a multirow-detector computer tomograph (Lightspeed, GEMS). The examination included PET with FDG and one CT acquisition with 80 mA. For CT, the following parameters were used: 140 kV, 80 mA, reconstructed slice thickness 5 mm, scan length 867 mm, AT 22.5 s. CT data were used for attenuation correction as well as image co-registration. Image analysis was performed on an Entegra work-station (ELGEMS). All patients with symmetrical uptake within the neck, thorax and shoulder regions were selected and the exact localisation of uptake determined (muscle, bone, fatty tissue or articulation). In 17 of the 638 patients (2.5%), increased, symmetrical FDG uptake in the shoulder region in a typical pattern was found. If extensive, this pattern included FDG activity comparable to brain activity in the lower cervical spine, the shoulder region and the upper thoracic spine in the costovertebral region. A less extensive pattern only involved intermediate FDG uptake in the lower cervical spine and shoulder region or in the shoulder region alone. In seven female patients (average 32.3 years), the extensive uptake pattern was seen. The average body mass index (BMI) was 19.0 (range 16.8-23.4). In the other ten patients (two male, eight female, average age 37.1 years), the average BMI was 22.7 (18.7-27.7). In all patients, the soft tissue uptake was clearly localised within the fatty tissue of the shoulders as demonstrated by PET/CT co-registration. The uptake in the region of the thoracic spine was localised in the region of the costovertebral joints. Symmetrical FDG uptake in the shoulder, neck and thoracic spine region is probably related to uptake in adipose tissue, especially in underweight patients. Hypothetically, this FDG uptake could represent activated brown adipose tissue during increased sympathetic nerve system (SNS) activity due to cold stress.

Because anatomical information on fluorine-18 fluorodeoxyglucose (FDG) whole-body positron emission tomography (PET) images is limited, combination with structural imaging is often important. In principle, software co-registration of PET and computed tomography (CT) data or dual-modality imaging using a combined PET-CT camera has an important role to play, since "hardware-co-registered" images are thereby made available. A major unanswered question is under which breathing protocol the respiration level in the CT images of a patient will best match the PET images, which represent summed images over many breathing cycles. To address this issue, 28 tumour patients undergoing routine FDG PET examinations were included in this study. In ten patients, PET and CT were performed using a new combined high-performance in-line PET-CT camera without the need for repositioning of the patient, while in 18 patients imaging was performed on separate scanners located close to each other. CT was performed at four respiration levels: free breathing (FB), maximal inspiration (MaxInsp), maximal expiration (MaxExp) and normal expiration (NormExp). The following distances were measured: (a) between a reference point taken to be the anterior superior edge of intervertebral disc space T10-11 and the apex of the lung, (b) from the apex of the lung to the top of the diaphragm, (c) from the apex of the lung to the costo-diaphragmatic recess and (d) from the reference point to the lateral thoracic wall. Differences between CT and corresponding PET images in respect of these distances were compared. In addition, for each of 15 lung tumours in 12 patients, changes in tumour position between PET and CT using the same protocol were measured. CT during NormExp showed the best fit with PET, followed by CT during FB. The mean differences in movement of the diaphragmatic dome on CT during NormExp, FB, MaxInsp and MaxExp, as compared with its level on PET scan, were, respectively, 0.4 mm (SD 11.7), -11.6 mm (13.3), -44.4 mm (25.5) and -9.5 mm (25.6). CT acquired in MaxExp and MaxInsp is not suitable for image co-registration owing to the poor match of images in MaxInsp and because of difficulties with patient performance in MaxExp. With reference to lung lesions, NormExp showed the best results, with a higher probability of a good match and a smaller range of measured values in comparison with FB. Image misregistration in combined PET-CT imaging can be minimized to dimensions comparable to the spatial resolution of modern PET scanners. For PET-CT image co-registration, the use of a normal expiration breath-hold protocol for CT acquisition is recommended, independent of whether combined PET-CT systems or stand-alone systems are used.

In a study population of patients suspected of having infected total hip replacements, FDG PET performed similarly to three-phase bone scintigraphy. FDG PET was more specific but less sensitive than conventional radiography for the diagnosis of infection.

Combined positron emission tomographic (PET)/computed tomographic (CT) scanners allow the use of CT data for attenuation correction of PET images. Eight patients with cancer underwent PET/CT scanning. Transmission scanning was performed with conventional attenuation correction and with CT scanning during maximum inspiration and normal expiration. Image quality was visually compared and fluorine 18 activities were measured in volumes of interest in the lung and myocardium. Analysis of variance for repeated measures revealed a significant decrease (P =.0001) in measured activities between PET images corrected with CT data acquired during maximum inspiration and those corrected with the conventional attenuation correction method or with CT data acquired during normal expiration. Deep inspiration during CT can result in severe deterioration in the final PET image.