Effect of the positron range of 18F, 68Ga and 124I on PET/CT in lung-equivalent materials.

PURPOSE: The aim of this study was to investigate the effect of positron range on visualization and quantification in (18)F, (68)Ga and (124)I positron emission tomography (PET)/CT of lung-like tissue. METHODS: Different sources were measured in air, in lung-equivalent foams and in water, using a clinical PET/CT and a microPET system. Intensity profiles and curves with the cumulative number of annihilations were derived and numerically characterized. RESULTS: (68)Ga and (124)I gave similar results. Their intensity profiles in lung-like foam had a peak similar to that for (18)F, and tails of very low intensity, but extending over distances of centimetres and containing a large fraction of all annihilations. For 90% recovery, volumes of interest with diameters up to 50 mm were required, and recovery within the 10% intensity isocontour was as low as 30%. In contrast, tailing was minor for (18)F. CONCLUSION: Lung lesions containing (18)F, (68)Ga or (124)I will be visualized similarly, and at least as sharp as in soft tissue. Nevertheless, for quantification of (68)Ga and (124)I large volumes of interest are needed for complete activity recovery. For clinical studies containing noise and background, new quantification approaches may have to be developed.

Identification of a shine-through artifact in the trachea with (124)I PET/CT.

UNLABELLED: The presence of (124)I in tissue near the trachea can cause a phenomenon that might be called shine-through. The effect is due to high-energy positrons that cross the air-filled trachea and annihilate at the opposite tracheal wall, incorrectly suggesting uptake at that location. METHODS: We investigated shine-through using (124)I, (68)Ga, and (18)F PET/CT scans of a neck phantom. Additionally, we evaluated (124)I studies of 29 patients with differentiated thyroid cancer who underwent imaging for postsurgical staging. RESULTS: In the phantom studies with a 0.1-mL (124)I source, the relative intensity of shine-through decreased from 7% to nearly zero when the thickness of the positron-stopping layer was increased from 0.3 to 3.85 mm. In patients, shine-through was observed in 5 of the 29 studies, with intensities between 0.7% and 14%. CONCLUSION: Shine-through appears rather common in differentiated thyroid cancer. Recognition is important for identification of real lesions, calculation of uptake, and dosimetry.

Lung-uptake and -washout of MIBG in sarcoidosis.

BACKGROUND: The aim of this study was to evaluate the uptake and -washout of I-123 meta-iodobenzylguanidine (MIBG), reflecting norepinephrine metabolism, in the lungs in patients with sarcoidosis. METHODS: Lung I-123 MIBG kinetics was assessed in 43 patients with sarcoidosis. The range of disease duration was 1-16 years (median: 3 years). Thirteen patients had radiographic stage 0-I, 30 patients had radiographic stage II-IV. Serological clinical parameters and small fibre neuropathy, as assessed by temperature threshold testing (TTT) were measured in 39/43 patients. 31/39 patients had an abnormal TTT. Eleven healthy controls participated in this study. Both dual head planar and dual headed SPECT images of the thoracic regions were made. The uptake of I-123 MIBG and the washout percentage were calculated in sarcoidosis patients and compared with the healthy persons. RESULTS: Lung I-123 MIBG uptake in patients with sarcoidosis did not differ from controls. The lung washout of I-123 MIBG was significantly (p

Effects of radiotherapy planning with a dedicated combined PET-CT-simulator of patients with non-small cell lung cancer on dose limiting normal tissues and radiation dose-escalation: a planning study.

BACKGROUND AND PURPOSE: To investigate the effect of radiotherapy planning with a dedicated combined PET-CT simulator of patients with locally advanced non-small cell lung cancer. PATIENTS AND METHODS: Twenty-one patients underwent a pre-treatment simulation on a dedicated hybrid PET-CT-simulator. For each patient, two 3D conformal treatment plans were made: one with a CT based PTV and one with a PET-CT based PTV, both to deliver 60Gy in 30 fractions. The maximum tolerable prescribed radiation dose for CT versus PET-CT PTV was calculated based on constraints for the lung, the oesophagus, and the spinal cord, and the Tumour Control Probability (TCP) was estimated. RESULTS: For the same toxicity levels of the lung, oesophagus and spinal cord, the dose could be increased from 55.2+/-2.0Gy with CT planning to 68.9+/-3.3Gy with the use of PET-CT (P=0.002), with corresponding TCP's of 6.3+/-1.5% for CT and 24.0+/-5.6% for PET-CT planning (P=0.01). CONCLUSIONS: The use of a combined dedicated PET-CT-simulator reduced radiation exposure of the oesophagus and the lung, and thus allowed significant radiation dose escalation whilst respecting all relevant normal tissue constraints.

Association of small fiber neuropathy with cardiac sympathetic dysfunction in sarcoidosis.

BACKGROUND AND AIM: Recently we found that small fiber neuropathy (SFN) occurs frequently in sarcoidosis. Autonomic dysfunction may be a feature of SFN. Since cardiac autonomic dysfunction has been identified as a strong predictor of morbidity and mortality, recognition of cardiac autonomic involvement is of clinical relevance. It was hypothesised that SFN might be related to cardiac sympathetic denervation in sarcoidosis. METHODS: In the present study 45 consecutive sarcoidosis patients (13 without SFN assessed by thermal threshold testing (TTT), 32 with SFN (abnormal TTT) were enrolled. To rule out bias due to myocardial ischemia, cases with abnormal Thallium (201Tl) perfusion scintigraphy were excluded (n = 2). Cardiovascular autonomic function testing (Ewing tests) and 123I-MIBG (metaiodobenzylguanidine) scintigraphy were used to assess cardiac autonomic function. Further cardiac diagnostic work-up included ECG, Holter recording and echo Doppler cardiography. RESULTS: Mild to moderate heterogeneity of 123I-MIBG uptake regional in the myocardium was demonstrated in a substantial number of the studied sarcoidosis population, especially in those with SFN (abnormal TTT). Mean inferior-anterior ratios were 0.85+/-0.17 (SFN) and 1.0+/-0.17 (no SFN; p = 0.003), respectively. Four out of the 14 cases with abnormal MIBG scintigraphy and SFN showed an abnormal Ewing test. CONCLUSION: Cardiac sympathetic dysfunction assessed by use of 123I-MIBG myocardial scanning appeared to be heterogeneous in sarcoidosis patients and dependent on the presence or absence of SFN. MIBG scintigraphy may be of additional value in the management and follow-up of sarcoidosis patients. Future study is warranted to explore possible prognostic and therapeutic implications of these findings in sarcoidosis.

Evaluation of a short dynamic 18F-fluoride PET/CT scanning method to assess bone metabolic activity in spinal orthopedics.

OBJECTIVE: A complication after spinal fusion surgery is pseudarthrosis, but its radiological diagnosis is of limited value. (18)F-fluoride PET with its ability to assess bone metabolism activity could be of value. The goal of this study was to assess the clinical feasibility of calculating the static standardized uptake value (SUV) from a short dynamic scan without the use of blood sampling, thereby obtaining all dynamic and static parameters in a scan of only 30 min. This approach was tested on a retrospective patient population with persisting pain after spinal fusion surgery. METHODS: In 16 patients, SUVs (SUV max, SUV mean) and kinetic parameters (K 1, k 2, k 3, v b, K i,NLR, K 1/k 2, k 3/(k 2 + k 3), K i,patlak) were derived from static and dynamic PET/CT scans of operated and control regions of the spine, after intravenous administration of 156-214 MBq (18)F-fluoride. Parameter differences between control and operated regions, as well as between pseudarthrosis and fused segments were evaluated. SUVmean at 30 and 60 min was calculated from kinetic parameters obtained from the dynamic data set (SUV mean,2TCM). Agreement between measured and calculated SUVs was evaluated through Bland-Altman plots. RESULTS: Overall, statistically significant differences between control and operated regions were observed for SUV max, SUV mean, K i,NLR, K i,patlak, K 1/k 2 and k 3/(k 2 + k 3). Diagnostic CT showed pseudarthrosis in 6/16 patients, while in 10/16 patients, segments were fused. Of all parameters, only those regarding the incorporation of bone [K i,NLR, K i,patlak, k 3/(k 2 + k 3)] differed statistically significant in the intervertebral disc space between the pseudarthrosis and fused patients group. The mean values of the patient-specific blood clearance rate [Formula: see text] differed statistically significant between the pseudarthrosis and the fusion group, with a p value of 0.011. This may correspond with the lack of statistical significance of the SUV values between pseudarthrosis and fused patients. Bland-Altman plots show that calculated SUV mean,2TCM values corresponded well with the measured SUV mean values. CONCLUSION: This study shows the feasibility of a 30-min dynamic (18)F-fluoride PET/CT scanning and this may provide dynamic parameters clinically relevant to the diagnosis of pseudarthrosis.

Assessment of bone graft incorporation by 18 F-fluoride positron-emission tomography/computed tomography in patients with persisting symptoms after posterior lumbar interbody fusion.

BACKGROUND: Posterior lumbar interbody fusion (PLIF) is a method that allows decompression of the spinal canal and nerve roots by laminectomy combined with fusion by means of intervertebral cages filled with bone graft and pedicle screw fixation. Conventional imaging techniques, such as plain radiography and computed tomography (CT), have limitations to assess bony fusion dynamics. METHODS: In 16 PLIFs of 15 patients with persisting symptoms, positron-emission tomography (PET)/CT scans were made 60 min after intravenous administration of 156 to 263 MBq of 18 F-fluoride, including 1-mm sliced, high-dose, non-contrast-enhanced CT scanning. Maximal standard uptake values (SUVmax) of various regions were calculated and correlated with abnormalities on CT. RESULTS: Subsidence of the cages into the vertebral endplates was the most frequently observed abnormality on CT (in 16 of 27 or 59% of evaluable endplates). Endplate SUVmax values were significantly higher for those patients with pronounced (p < 0.0001) or moderate (p < 0.013) subsidence as compared to those with no subsidence. Additionally, a significant correlation between vertebral and ipsilateral pedicle screw entrance SUVmax values (p < 0.009) was found, possibly indicating posterior transmission of increased bone stress. In our patient group, intercorporal fusion was seen on CT in 63% but showed no correlation to intercorporal SUVmax values. CONCLUSIONS: With the use of 18 F-fluoride PET/CT, intervertebral cage subsidence appeared to be a prominent finding in this patient group with persisting symptoms, and highly correlating with the degree of PET hyperactivity at the vertebral endplates and pedicle screw entry points. Further study using 18 F-fluoride PET/CT should specifically assess the role of metabolically active subsidence in a prospective patient group, to address its role in nonunion and as a cause of persisting pain.