Can a ToF-PET photon attenuation reconstruction test stopping-power estimations in proton therapy? A phantom study.

Objective. The aim of the phantom study was to validate and to improve the computed tomography (CT) images used for the dose computation in proton therapy. It was tested, if the joint reconstruction of activity and attenuation images of time-of-flight PET (ToF-PET) scans could improve the estimation of the proton stopping-power.Approach. The attenuation images, i.e. CT images with 511 keV gamma-rays (γCTs), were jointly reconstructed with activity maps from ToF-PET scans. Theß+activity was produced with FDG and in a separate experiment with proton-induced radioactivation. The phantoms contained slabs of tissue substitutes. The use of theγCTs for the prediction of the beam stopping in proton therapy was based on a linear relationship between theγ-ray attenuation, the electron density, and the stopping-power of fast protons.Main results. The FDG based experiment showed sufficient linearity to detect a bias of bony tissue in the heuristic look-up table, which maps between x-ray CT images and proton stopping-power.γCTs can be used for dose computation, if the electron density of one type of tissue is provided as a scaling factor. A possible limitation is imposed by the spatial resolution, which is inferior by a factor of 2.5 compared to the one of the x-ray CT.γCTs can also be derived from off-line, ToF-PET scans subsequent to the application of a proton field with a hypofractionated dose level.Significance. γCTs are a viable tool to support the estimation of proton stopping with radiotracer-based ToF-PET data from diagnosis or staging. This could be of higher potential relevance in MRI-guided proton therapy.γCTs could form an alternative approach to make use of in-beam or off-line PET scans of proton-inducedß+activity with possible clinical limitations due to the low number of coincidence counts.

Quantitative performance evaluation of 124I PET/MRI lesion dosimetry in differentiated thyroid cancer.

The aim was to investigate the quantitative performance of 124I PET/MRI for pre-therapy lesion dosimetry in differentiated thyroid cancer (DTC). Phantom measurements were performed on a PET/MRI system (Biograph mMR, Siemens Healthcare) using 124I and 18F. The PET calibration factor and the influence of radiofrequency coil attenuation were determined using a cylindrical phantom homogeneously filled with radioactivity. The calibration factor was 1.00 ± 0.02 for 18F and 0.88 ± 0.02 for 124I. Near the radiofrequency surface coil an underestimation of less than 5% in radioactivity concentration was observed. Soft-tissue sphere recovery coefficients were determined using the NEMA IEC body phantom. Recovery coefficients were systematically higher for 18F than for 124I. In addition, the six spheres of the phantom were segmented using a PET-based iterative segmentation algorithm. For all 124I measurements, the deviations in segmented lesion volume and mean radioactivity concentration relative to the actual values were smaller than 15% and 25%, respectively. The effect of MR-based attenuation correction (three- and four-segment µ-maps) on bone lesion quantification was assessed using radioactive spheres filled with a K2HPO4 solution mimicking bone lesions. The four-segment µ-map resulted in an underestimation of the imaged radioactivity concentration of up to 15%, whereas the three-segment µ-map resulted in an overestimation of up to 10%. For twenty lesions identified in six patients, a comparison of 124I PET/MRI to PET/CT was performed with respect to segmented lesion volume and radioactivity concentration. The interclass correlation coefficients showed excellent agreement in segmented lesion volume and radioactivity concentration (0.999 and 0.95, respectively). In conclusion, it is feasible that accurate quantitative 124I PET/MRI could be used to perform radioiodine pre-therapy lesion dosimetry in DTC.

Lowest effective 131I activity for thyroid remnant ablation of differentiated thyroid cancer patients. Dosimetry-based model for estimation.

AIM: A theoretical dosimetry-based model was applied to estimate the lowest effective radioiodine activity for thyroid remnant ablation of low-risk differentiated thyroid cancer patients. PATIENTS, METHODS: The model is based on the distribution of the absorbed (radiation) dose per administered radioiodine activity and the absorbed dose threshold of 300 Gy for thyroid remnants, the level believed to destroy most thyroid remnants. For this purpose, ¹²4I PET/CT images of 49 thyroidectomised patients were retrospectively analysed to measure the distribution of the (average) absorbed doses to thyroid remnant per administered ¹³¹I activity. The fraction of thyroid remnants that received at least 300 Gy was determined for standard activities between 0.37 and 5.55 GBq. The lower activity was considered to be equally effective to that obtained with higher activity if the (absolute) fraction difference was below 5%. RESULTS: A total of 62 thyroid remnants were included. The medians and ranges (in parentheses) for the absorbed dose per unit 131I activity were 359 Gy/GBq (34 to 1825 Gy/GBq). The fractions of thyroid remnants receiving more than 300 Gy at different therapy activities (within parentheses) were 60% (1.11 GBq), 76% (1.85 GBq), 79% (2.22 GBq), and 81-82% for activities between 2.59 and 3.70 GBq. The therapy activity of 1.11 GBq is considerably less effective than that of 1.85 or 2.22 GBq; therapy activities were equally effective in the range between 2.22 to 3.70 GBq. CONCLUSION: On the basis of the model and the patients' data included, the lowest effective therapy activity appears to be approximately 2.2 GBq to ablate thyroid remnants. The results of this study may help to guide the design of prospective clinical studies.

Monte Carlo-based 3-dimensional dosimetry of salivary glands in radioiodine treatment of differentiated thyroid cancer estimated using 124I PET.

AIM: Salivary gland toxicity is of concern in radioiodine treatment of thyroid cancer. Toxicity is often observed while the estimated radiation absorbed dose (AD) values are below expected toxicity thresholds. Monte Carlo-based voxelized 3-dimensional radiobiological dosimetry (3D-RD) calculations of the salivary glands from eight metastatic thyroid cancer patients treated with 131I are presented with the objective of resolving this discrepancy. METHODS: GEANT4 Monte Carlo simulations were performed for 131I, based on pretherapeutic 124I PET/CT imaging corrected for partial volume effect, and the results scaled to the therapeutic administered activities. For patients with external regions of high uptake proximal to the salivary glands, such as thyroid remnants or lymph node metastases, separate simulations were run to quantify the AD contributions from both (A) the salivary glands themselves, and (B) the external proximal region of high uptake (present for five patients). The contribution from the whole body outside the field of view was also estimated using modeling. Voxelized and average ADs and biological effective doses (BEDs) were calculated. RESULTS: The estimated average therapeutic ADs were 2.26 Gy considering all contributions and 1.94 Gy from the self-dose component only. The average contribution from the external region of high uptake was 0.54 Gy. This difference was more pronounced for the submandibular glands (2.64 versus 2.10 Gy) compared to the parotid glands (1.88 Gy versus 1.78 Gy). The BED values were on average only 6.6 % higher than (2.41 Gy) the ADs. CONCLUSION: The external sources of activity contribute significantly to the salivary gland AD, however neither this contribution, nor the radiobiological effect quantified by the BED are in themselves sufficient to explain the clinically observed toxicity.

124I-PET/CT images of differentiated thyroid cancer patients. Distinguishing lymph node metastases from thyroid remnants using kinetic quantities.

UNLABELLED: For an adequate therapy planning and staging of patients with differentiated thyroid cancer (DTC), the correct assignment of thyroid remnants (TRs) and lymph node metastases (LMs) is important. PATIENTS, METHOD: We retrospectively analyzed whether kinetic quantities can help improving LM assignment using serial 124I-PET/CT data. 127 patients with a total of 317 lesions (TR: n = 265; LM: n = 52) received pre-therapy 124I-PET/CT lesion dosimetry using images 24 h and > 96 h after 124I administration. For each lesion, maximum activity concentration (MAC) at 24 h and effective half-life (EHL) were determined. Moreover, the product of MAC and EHL was also investigated as a quantity and is referred to CAQ (cumulated activity proportional quantity). In addition, differences between endogenous and exogenous thyroid-stimulating hormone (TSH) stimulation and between papillary (PTC) and follicular thyroid cancer (FTC) were investigated. RESULTS, CONCLUSION: The median MAC, EHL, and CAQ values in TR were significantly higher than in LM but a clinically relevant cut-off value could not be determined because of high overlapping regions. No significant differences for the three quantities were found for the mode of TSH stimulations, but a significant difference for MAC and CAQ between PTC and FTC.

Estimation of tumour mass in patients with differentiated thyroid carcinoma using serum thyroglobulin.

UNLABELLED: Serum thyroglobulin (Tg) is a reliable tumour marker in follow-up of patients with differentiated thyroid carcinoma (DTC). A positive correlation between Tg level and tumour mass was recently observed, but no attempts were made to derive a numerical relation. The aim of this study was to derive a numerical relationship between serum Tg level and tumour mass that allows optimizing the diagnostic procedures. PATIENTS, METHOD: 78 DTC patients with tumour lesions in either 124I-NaI or 18F-FDG PET/CT were included. For each patient, the total tumour mass was determined functionally in iodine- and FDG-positive lesions as well as morphologically in only CT-positive lesions. The serum Tg level was measured under TSH stimulation prior to imaging. Regression analyses were performed to derive an approach for estimation of the total tumour mass based on Tg levels. RESULTS: A positive correlation of serum Tg and tumour mass was confirmed and a mathematical expression was given to estimate the tumour mass along with its 95% confidence interval using only the serum Tg level. The results demonstrated that the range of predicted tumour mass was higher per serum Tg unit for iodine-positive lesions than for FDG-positive tumour lesions and was higher for follicular than for papillary thyroid carcinoma. CONCLUSION: This study provides an approach to estimate the tumour mass and its 95% confidence intervals in DTC patients using the serum Tg level. The range of the estimated tumour mass for a given Tg level is rather large, and therefore, the approach is of limited value in clinical application.

Neural substrates of good and poor recovery after hemiplegic stroke: a serial PET study.

In this study, we used positron emission tomography (PET) at two different time points to study the temporal evolution of reorganization in patients with good and those without motor recovery from hemiplegia after the occurrence of a stroke. Ten hemiplegic patients with a first subcortical stroke and five healthy control subjects were scanned during passive and active movements at an interval of 8 weeks. PET1 was performed 22.8 ± 7.8 days after the index stroke. At PET2, 8 weeks later, patients were dichotomized to either good recovery or no recovery according to the upper extremity motor component of the Fugl-Meyer score. Increases of regional cerebral blood flow (rCBF) and comparison between groups at PET1 and PET2 were assessed using statistical parametric mapping. At PET 1, activation was found bilaterally in the inferior parietal cortex. Eight weeks later, patients with good recovery showed maximum activation in the contralateral primary somatosensory cortex and overactivation of the contralateral inferior parietal cortex. Patients with poor recovery showed bilateral activation with a maximum in the somatosensory cortex. Studies correlating activation patterns with quality of recovery may identify the neuroanatomical substrates that subserve improved motor function. Such studies may also guide the development of more effective rehabilitative interventions after the occurrence of stroke.

Quantitative imaging of (124)I with PET/ CT in pretherapy lesion dosimetry. Effects impairing image quantification and their corrections.

Iodine-131-labelled agents are successfully used in cancer treatment. In the pretherapy dosimetry approach, positron emission tomography/computed tomography (PET/CT) using (124)I provides a modality to estimate absorbed dose to tumours and can be considered as the preferred imaging method for this purpose in (131)I radiopharmaceutical therapies. For accurate dosimetry, serial measurements of activity concentrations (ACs) over an appropriate time period are necessary. Consequently, accurate AC determination is of paramount importance in PET/CT-based lesion dosimetry using (124)I-labelled agents. After presenting an historical overview of (124)I clinical application, this review focuses on factors impairing PET image quantification accuracy and on methods of correcting for these effects. Specifically, the emission of prompt gamma photons in the (124)I decay process that are detected in coincidence with each other and with the annihilation photon, and the low (124)I positron branching ration of only 23% raise concerns regarding image quantification accuracy. This review discusses this prompt gamma effect, its impact and approaches to correct for this phenomenon. In (124)I lesion dosimetry, recovery coefficients (RCs) are commonly used to compensate primarily for partial-volume effect but also, in a simplistic way, for prompt gamma coincidence effect; the main methodological factors affecting the RC-corrected (124)I AC are described. Finally, special issues in image (124)I quantification are reviewed, including coadministration of high therapeutic activities of 131I, shine-through artefact, and transmission-contamination effect occurring in stand-alone PET systems.

Thyroid remnant dose: 124I-PET/CT dosimetric comparison of rhTSH versus thyroid hormone withholding before radioiodine remnant ablation in differentiated thyroid cancer.

AIM: Recombinant human thyroid-stimulating hormone (rhTSH) recently was approved as an alternative to thyroid hormone withholding (THW) to elevate TSH for thyroid remnant ablation in differentiated thyroid carcinoma patients. High ablation success rates are reported with diverse rhTSH-aided (131)I activities. Improved renal function causes approximately 50% faster radioiodine clearance under euthyroidism versus hypothyroidism. Knowledge of comparative remnant radioiodine kinetics, particularly the remnant radiation dose in Gy/GBq of administered (131)I activity (RDpA), could assist in choosing rhTSH-aided ablative activities. MATERIAL AND METHODS: To compare the RDpA, determined through (124)I-positron emission tomography/computed tomography (PET/CT), under the two stimulation methods, we retrospectively divided into two groups 55 consecutive totally-thyroidectomized, radioiodine-naïve patients. The rhTSH group (n=16) received (124)I on thyroid hormone, 24 h after two consecutive daily intramuscular injections of rhTSH, 0.9 mg. The THW group (n=39) received (124)I after weeks-long THW, when serum TSH first measured > or = 25 mIU/L. We performed PET investigations 4 h, 24 h, 48 h, 72 h and 96 h and PET/CT 25 h after (124)I administration. RESULTS: Median stimulated serum thyroglobulin was 15 times higher (p=0.023) and M1 disease almost twice as prevalent (p=0.05) in rhTSH versus THW patients. Mean+/-standard deviation RDpA was statistically equivalent between the groups: rhTSH, 461+/-600 Gy/GBq, THW, 302+/-329 Gy/GBq, two-sided p=0.258. CONCLUSIONS: rhTSH or THW deliver statistically equivalent radiation doses to thyroid remnant and may be chosen based on safety, quality-of-life, convenience and pharmacoeconomic factors. Institutional fixed radioiodine activities formulated for use with THW need not be adjusted for rhTSH-aided ablation.

Calcification-related absorption in thyroid scintigraphy.

UNLABELLED: The enhanced absorption of X-rays in calcified structures is a basic prerequisite for performing conventional bone radiography. On the other hand, nothing has been reported on possible absorption effects of 'calcifications' as frequent findings in thyroid nodules or in the sternal bone / sternoclavicular joints. This may be caused by the general opinion, that the high energy of 99mTc-photons (140 keV) do not make visible absorptions effects very likely. PATIENTS, METHODS: To prove possible absorption effects of calcifications on thyroid scintigraphy experimentally, effects of calcium absorbers were tested on a technetium flood phantom. Furthermore, absorption effects of various calcifications (discs of calcium sulphate and calcium carbonate with varying thickness) on normal thyroid tissue and autonomous nodules were simulated in a thyroid phantom. CT 130 kV-images of 46 consecutive patients were checked for presence of retrosternal or retroclavicular growth of the thyroid gland and to measure the extent and density of the sternal bone and calcified intrathyroidal nodules. In addition, clinical cases are presented in which a possible absorption by calcifications seems to be likely. RESULTS: Bony structures in front of the thyroid gland or calcified intrathyroidal nodules could be seen on CT in 24/46 patients. The mean averaged density was 219 Houndsfield units (SD: 89 HU). The quantitative measurements using a 99mTc-flood source showed a mean absorption of 4.9%. In a thyroid phantom, absorption effects were visible only in 3/20 positions of the calcium discs over the thyroid phantom. Focal effects could be better detected in situations of only moderate uptake of the surrounding tissue. A dependence of absorption and chemistry (sulphate, carbonate) could not be found. CONCLUSION: Visible absorption effects caused by sternal bone or thyroid calcifications are seldom but potentially able to diminish the visible uptake and should be taken into account when interpreting thyroid scintigrams.

Combined metabolic and morphologic imaging in thyroid carcinoma patients with elevated serum thyroglobulin and negative cervical ultrasonography: role of 124I-PET/CT and FDG-PET.

PURPOSE: This study sought to compare iodine-124 positron emission tomography/computed tomography (124I-PET/CT) and 2-[18F]fluoro-2-deoxy-D: -glucose- (FDG-) PET in the detection of recurrent differentiated thyroid carcinoma (DTC) lesions in patients with increasing serum thyroglobulin (Tg), Tg-antibodies, or both, but without pathological cervical ultrasonography. We assessed the lesion detection accuracy of 124I-PET alone, CT alone, (124)I-PET/CT, FDG-PET, and all these modalities combined. MATERIAL AND METHODS: The study included 21 patients (9 follicular, 12 papillary DTC) who had been rendered disease-free by thyroidectomy and radioiodine treatment (RIT) and followed up for 21-275 months after the last RIT. In all patients, FDG-PET was performed first. Within 1 week, 124I-PET/CT was performed 24 h after oral administration of 43 +/- 11 MBq 124I. Imaging results were correlated with further clinical follow-up with (n = 12) or without (n = 9) post-study histology as the reference standard. RESULTS: The sensitivities for DTC lesion detection were: 124I-PET, 49%; CT, 67%; 124I-PET/CT, 80%; FDG-PET, 70%; and all modalities combined, 91%. For local recurrences (distant metastases), the sensitivities were: 124I-PET, 60% (45%); CT, 20% (84%); and FDG-PET, 65% (71%). One-third of lesions demonstrated pathological tracer uptake with both 124I- and FDG-PET, while two-thirds were positive with only one of these modalities. CONCLUSION: Used together, 124I-PET and CT allow localization of foci of highly specific 124I uptake as well as non-iodine-avid lesions. The combination of 124I-PET/CT and FDG-PET improves restaging in recurrent DTC by enabling detection on whole-body scans of local recurrence or metastases that are often not found if only one of the methods or other imaging modalities are applied.

124-iodine positron emission tomography/computed tomography dosimetry in pediatric patients with differentiated thyroid cancer.

AIM: Publications on 124-iodine (124I-)-positron emission tomography/computed tomography (PET/CT) dosimetry contain few if any data on pediatric patients with differentiated thyroid carcinoma (DTC). Aim of our study is to determine safety and informativeness of 124I-PET/CT dosimetry in DTC patients2Gy blood dose portending serious myelotoxicity. RESULTS: Besides hypothyroid fatigue, no symptoms were noted. In 4 dosimetry procedures before the first radioiodine therapy, RDpAs were generally high (median 288 Gy/GBq, range 59-648 Gy/GBq). LDpAs (4 lymph node metastases) were much lower (median 6.5 Gy/GBq, range 1-9 Gy/GBq). CBAs were high (median 26 GBq, range 19-42, n=5). Disease management was modified or disease extent clarified in 2/4 patients. CONCLUSIONS: A standard adult 124I-PET/CT dosimetry protocol appears to be safe and informative in pediatric DTC patients.

[The effect of different chemoembolization materials on CT-based attenuation correction in PET/CT]. / Effekt verschiedener Chemoembolisationsmaterialien auf die CT-basierte Schwächungskorrektur der PET/CT.

PURPOSE: Primary and secondary hypervascularized liver tumors may be treated with transarterial chemoembolization (TACE). The purpose of this study was to experimentally quantify the effect of different chemoembolization materials on the PET activity concentration in PET/CT. MATERIALS AND METHODS: Different concentrations of lipiodol, tungsten, tantalum, and a different number of platinum coils embedded in a carrier substance were placed in a liver phantom. An insert filled with only the carrier substance served as the negative control. The liver phantom was placed in a body phantom. The liver phantom was filled with 63.3 KBq [18-F]-Fluor-2-deoxy-D-glucose (FDG)/ml water, the body phantom was filled with 19.7 KBq FDG/ml water. PET/CT was performed and PET attenuation correction was performed based on the CT data. We defined: Activity concentration over embolization material (kBq/ml) approximately measured activity concentration; activity concentration over negative control (kBq/ml) approximately real activity concentration. An overestimation of the activity concentration was quantified by the following ratio: Activity concentration overestimation = activity concentration over embolization material (kBq/ml)/activity concentration over negative control (kBq/ml). RESULTS: All chemoembolization materials led to an overestimation of the PET activity concentration when using CT information for PET attenuation correction. The extent of overestimation is dependent on the concentration and the density of the chemoembolizing agent. PET activity overestimation was 11-151% with lipiodol, 34-1827% with tungsten, 16-1205% with tantalum, and 4-29% with platinum coils. CONCLUSION: Conventional chemoembolization materials cause an overestimation of the PET activity concentration in CT-based attenuation-corrected PET/CT images. This is of importance for the clinical routine since activity concentration quantification may not be used in the presence of chemoembolizing agents for imaging follow-up. If an increased FDG uptake is detected after transarterial chemoembolization, non-attenuation-corrected PET images must be assessed in addition to the attenuation-corrected images in order to differentiate artificially increased tracer uptake from a true increase in activity concentration of the tracer. The use of non-attenuating chemoembolizing materials (e.g. drug-eluting beads) for TACE may serve as an alternative to avoid embolization-associated PET artifacts.

124I-PET dosimetry in advanced differentiated thyroid cancer: therapeutic impact.

PURPOSE: This study evaluated the impact of (124)I-positron emission tomography (PET) dosimetry on post-primary surgery therapy in radioiodine-naïve patients with advanced differentiated thyroid cancer (DTC). PATIENTS, MATERIAL, METHODS: In each of 28 thyroidectomized patients with high-risk DTC (one or more of pT4, pN1 or pM1), we gave 23-50 MBq of (124)I as an oral capsule and performed PET dosimetry to calculate the individualized therapeutic (131)I activity that would, insofar as possible, achieve a radioiodine dose >or=100 Gy to all metastases without exceeding 2 Gy to the blood (a surrogate for bone marrow toxicity). We thus determined the absorbed lesion dose per GBq of administered 131I activity (LDpA) based on serial PET (4, 24, 48, 72 and 96 h after oral 124I intake) and PET/computed tomography (25 h after (124)I intake) and the critical blood activity (CBA) based on blood and whole-body radiation counting (2, 4, 24, 48, 72, 96 h after 124I intake). We compared the dosimetry-based interventions with our standard empirical protocol. RESULTS: 25 patients had a total of 126 iodine-positive metastases. 18 (72%) of the 25 had solely iodine-avid metastases, while seven (28%) had both iodine-avid and -non-avid metastases. In two patients (8%), none of the iodine-avid metastases could have been practically treated with a sufficient radiation dose. Relative to the empirical protocol, (124)I-PET dosimetry findings changed management in 7 (25%) patients, e.g. allowing application of activities >11 GBq (131)I. Further changes included implementation of hematological back-up in a patient found to be at risk of life-threatening marrow toxicity, and early multimodal therapy in 9 (32%) patients. CONCLUSION: 124I-PET dosimetry is a useful routine procedure in advanced DTC and may allow safer or more effective radioiodine activities and earlier multimodal interventions than do standard empirical protocols.

Development and clinical impact of thyroglobulin antibodies in patients with differentiated thyroid carcinoma during the first 3 years after thyroidectomy.

OBJECTIVE AND DESIGN: Cross-sectional studies have reported an increased prevalence of circulating thyroglobulin autoantibodies (TgAbs) in patients with differentiated thyroid carcinoma (DTC). With the advent of more sensitive assays, a longitudinal study monitoring the development of TgAb levels after ablative therapy was warranted. METHODS: One hundred and twelve consecutive patients with follicular cell-derived thyroid cancer were followed for 3 years. All patients had been thyroidectomized and received, on average, two radioiodine therapies. Residual tissue was quantified scintigraphically by 131I 24-h uptake. TgAb and thyroglobulin (Tg) serum levels were determined with a sensitive direct radioligand assay and an IRMA respectively. RESULTS: The prevalence of TgAbs at the initial examination was 29% (median 130 U/ml). During follow-up, TgAb levels rose transiently in one-tenth of the patients, but the prevalence of demonstrable TgAbs decreased to < 10% after 3 years. The median serum half-life of TgAbs in treated DTC patients was 10 weeks. At initial examination (when all patients still had residual thyroid tissue and 17 had metastases), rising TgAb levels were correlated with the inability to detect Tg in 4, 30 and 73% of the patients, when initial TgAbs were < 6, 6-50 or > 50 U/ml respectively. While the Tg recovery test was valid for all patients, an in vitro dilution assay with TgAb serum reduced Tg values by up to 32%. CONCLUSIONS: The development and course of TgAbs in DTC patients cannot be predicted by initial or residual tumour volume, TgAb or Tg levels. The presence of TgAbs, even in low concentrations, may cause Tg underestimation despite valid recovery tests in DTC patients.

Value of (124)I-PET/CT in staging of patients with differentiated thyroid cancer.

The aim of this study is to evaluate the clinical significance of (124)I positron emission tomography (PET) using a combined PET/CT tomograph in patients with differentiated thyroid carcinoma and to compare the PET/CT results with (131)I whole-body scintigraphy (WBS), dedicated PET and CT alone. Twelve thyroid cancer patients were referred for diagnostic workup and entered complete clinical evaluation, including histology, cytology, thyroglobulin level, ultrasonography, fluorine-18 fluorodeoxyglucose (FDG)-PET, FDG-PET/CT and CT. Lesion-based evaluation showed a lesion delectability of 56, 87 and 100% for CT, (124)I-PET, and combined (124)I-PET/CT imaging, respectively. Lesion delectability of (131)I-WBS was 83%. We conclude that (124)I-PET/CT imaging is a promising technique to improve treatment planning in thyroid cancer. It is particularly valuable in patients suffering from advanced differentiated thyroid cancer prior to radio-iodine therapy and in patients with suspected recurrence and potential metastatic disease.

FDG-PET/CT in re-staging of patients with lymphoma.

The aim of this study was to evaluate the clinical significance of combined fluorine-18 fluorodeoxyglucose positron emission tomography and computed tomography (FDG-PET/CT) in patients with lymphoma, and to compare the FDG-PET/CT staging results with those of FDG-PET and CT alone. Twenty-seven patients were studied. Each patient had clinical follow-up for >12 months and entered complete follow-up evaluation. Patient-based evaluation showed a sensitivity of 78% for CT alone, 86% for FDG-PET alone, 93% for CT and FDG-PET read side by side, and 93% for combined FDG-PET/CT imaging. Region-based evaluation showed a sensitivity for regional lymph node involvement of 61%, 78%, 91% and 96% respectively. FDG-PET/CT imaging is superior to CT alone ( P=0.02) and has additional benefit over FDG-PET alone due to exact anatomical localisation. We conclude that FDG-PET/CT imaging is accurate in re-staging lymphoma and offers advantages over separate FDG-PET and CT imaging.

Combined PET/CT with iodine-124 in diagnosis of spread metastatic thyroid carcinoma: a case report.

Iodine-124 positron emission tomography (PET) is a useful 3D imaging technique for diagnosis and management of thyroid diseases. The difficulty in interpretation of the PET scans with highly selective tracers, such as iodine-124, is the lack of identifiable anatomical structures, so an accurate anatomical localization of foci presenting abnormal uptake is problematic. Consequently, a combined PET/CT scanner can resolve these difficulties by co-registering PET and CT data in a single session allowing a correlation of functional and morphologic imaging. A case is presented where iodine-124 produced by a clinical cyclotron and FDG were used to acquire images with a combined PET/CT scanner for clinical staging. On the basis of the PET/CT exams the treatment of the patient was modified.

Cortical activation to auditory mismatch elicited by frequency deviant and complex novel sounds: a PET study.

The analysis of auditory deviant events outside the focus of attention is a fundamental capacity of human information processing and has been studied in experiments on Mismatch Negativity (MMN) and the P3a component in evoked potential research. However, generators contributing to these components are still under discussion. Here we assessed cortical blood flow to auditory stimulation in three conditions. Six healthy subjects were presented with standard tones, frequency deviant tones (MMN condition), and complex novel sounds (Novelty condition), while attention was directed to a nondemanding visual task. Analysis of the MMN condition contrasted with thestandard condition revealed blood flow changes in the left and right superior temporal gyrus, right superior temporal sulcus and left inferior frontal gyrus. Complex novel sounds contrasted with the standard condition activated the left superior temporal gyrus and the left inferior and middle frontal gyrus. A small subcortical activation emerged in the left parahippocampal gyrus and an extended activation was found covering the right superior temporal gyrus. Novel sounds activated the right inferior frontal gyrus when controlling for deviance probability. In contrast to previous studies our results indicate a left hemisphere contribution to a frontotemporal network of auditory deviance processing. Our results provide further evidence for a contribution of the frontal cortex to the processing of auditory deviance outside the focus of directed attention.