Oncological applications of positron emission tomography with fluorine-18 fluorodeoxyglucose

Positron emission tomography (PET) is now primarily used in oncological indication owing to the successful application of fluorine-18 fluorodeoxyglucose (FDG) in an increasing number of clinical indications at different stages of diagnosis, and for staging and follow-up. This review first considers the biological characteristics of FDG and then discusses methodological considerations regarding its use. Clinical indications are considered, and the results achieved in respect of various organs and tumour types are reviewed in depth. The review concludes with a brief consideration of the ways in which clinical PET might be improved.     

Fluorine-18 fluorodeoxyglucose dual-head positron emission tomography in the detection of recurrent differentiated thyroid cancer: preliminary results

In the follow-up of patients with thyroid cancer, it may be very difficult to identify the site of recurrence in the presence of persistently elevated or rising thyroglobulin (Tg) levels and negative iodine-131 whole-body scintigraphy (WBS). The aim of this study was to assess the feasibility of employing fluorine-18 fluorodeoxyglucose and a dual-head positron emission tomography (PET) camera to detect recurrent thyroid cancer in patients with elevated Tg levels and negative ¹³¹I WBS. Eleven patients suspect of having recurrent thyroid cancer (five males, six females; mean age 47 years; range 26–73 years) were studied with both ¹³¹I WBS and FDG using a dual-head PET camera. The suspicion that these patients had recurrent thyroid cancer was based on elevated Tg levels. Thyroid stimulating hormone (TSH) and Tg levels as well as antibodies to Tg were measured 3 weeks after the withdrawal of tri-iodothyronine. In patients in whom pathological uptake was seen on the PET images but who had no signs of recurrent thyroid cancer on WBS, ultrasonography and/or computed tomography or magnetic resonance imaging was performed followed by fine-needle aspiration cytology. The mean Tg and TSH levels after discontinuation of l-thyroxine were 156 ng/ml (range 4–815 ng/ml) and 84 mU/l (range 43–159 mU/l), respectively. None of the patients had antibodies to thyroglobulin. In seven out of ten patients with negative ¹³¹I WBS, FDG PET showed focally increased uptake in the head and neck region. In one patient, the site of increased uptake on the PET images corresponded with the site of increased ¹³¹I uptake. Malignancies with a diameter less than 1 cm (n=3) were not depicted by either CT or US. It is concluded that detection of recurrent thyroid cancer by means of FDG dual-head PET is feasible in patients with elevated Tg concentrations and negative ¹³¹I WBS. The results justify a prolongation of the study. Received 1 May and in revised form 11 June 1999     

Rapid detection of human infections with fluorine-18 fluorodeoxyglucose and positron emission tomography: preliminary results

The purpose of this study was to evaluate the feasibility of 2-[fluorine-18]fluoro-2-deoxy-d-glucose (FDG) and positron emission tomography (PET) for rapid detection of human infections. Eleven patients who were known or suspected to be harboring various infections were studied with FDG-PET. Dynamic scans over the putative infection sites were performed immediately after FDG (370 MBq) injection through 60 min, and static images including multiple projection images were then obtained. FDG uptake was assessed visually into four grades (0, normal; 1, probably normal; 2, probably abnormal; 3, definitely abnormal). For the semiquantitative index of FDG uptake in infections, the standardized uptake value of FDG normalized to the predicted lean body mass (SUV-lean, SUL) was determined from the images obtained at 50–60 min after FDG injection. PET results were compared with final clinical diagnoses. Eleven lesions in eight patients, which were interpreted as grade 2 or 3 by FDG-PET, were all concordant with active infectious foci. The SUL values of infections ranged from 0.97 to 6.69. In two patients, FDG-PET correctly showed no active infection. In one patient, it was difficult to detect infectious foci by FDG-PET due to substantial normal background uptake of FDG. In total, FDG-PET correctly diagnosed the presence or absence of active infection in 10 of 11 patients. Fusion images of PET with computed tomography showed the most intense FDG uptake to be within an abscess wall. In conclusion, FDG-PET appears to be a promising modality for rapid imaging of active human infections. More extensive clinical evaluation is warranted to determine the accuracy of this method. Received 5 March and in revised form 20 May 1998     

Optimal scan time for fluorine-18 fluorodeoxyglucose positron emission tomography in breast cancer

Fluorine-18 fluorodeoxyglucose positron emission tomography (FDG PET) has proven useful in the differentiation of various tumour entities, including breast cancer. In patients with primary breast cancer we performed a 3-h imaging protocol to examine possible improvements in tumour detectability and image contrast. Twenty-nine patients with primary breast cancer with a diameter of ≥2 cm that was demonstrated to be malignant by biopsy or surgery were injected with 370–740 MBq ¹⁸F-FDG and scanned in the prone position. Data were acquired 0–40 min, 1.5 h and 3.0 h after injection. After correction for measured attenuation, decay and scatter and iterative reconstruction, standardised uptake values (SUVs) and tumour-to-non-tumour and tumour-to-organ ratios were calculated. Visual analysis was performed using transverse, sagittal and coronal slices as well as 3D reprojection images. Tumour-to-non-tumour and tumour-to-organ ratios were significantly higher for the 3-h images than for the 1.5-h images. SUVs did not increase to the same extent. Lesion detectability was 83% in 1.5-h images compared to 93% in 3-h images. We conclude that tumour contrast in breast cancer is improved by starting the PET acquisition at 3 h p.i. rather than at 1.5 h p.i. Received 17 October and in revised form 8 December 1998     

The value of fluorine-18 fluorodeoxyglucose positron emission tomography in patients with medullary thyroid cancer

The early detection of metastases from medullary thyroid cancer (MTC) is important because the only curative therapy consists in surgical removal of all tumour tissue. There is no single sensitive diagnostic imaging modality for the localization of all metastases in patients with MTC. Therefore, in many cases several imaging modalities (e.g. ultrasonography, magnetic resonance imaging, computerized tomography and scintigraphy using pentavalent technetium-99m dimercaptosuccinic acid, thallium-201 chloride, indium-111 pentetreotide, anti-CEA antibodies or metaiodobenzylguanidine) must be performed consecutively in patients with elevated calcitonin levels until the tumour is localized. In this prospective study, we investigated the value of fluorine-18 fluorodeoxyglucose positron emission tomography ([¹⁸F]FDG PET) in the follow-up of patients with MTC. [¹⁸F]FDG PET examinations of the neck and the chest were performed in 20 patients with elevated calcitonin levels or sonographic abnormalities in the neck. Positive [¹⁸F]FDG findings were validated by histology, computerized tomography or selective venous catheterization. [¹⁸F]FDG PET detected tumour in 13/17 patients (nine cases were validated by histology, four by computerized tomography). Five patients showed completely negative PET scans (of these cases, one was true-negative and four false-negative). One patient with [¹⁸F]FDG accumulation in pulmonary lesions from silicosis and one patient with a neck lesion that was not subjected to histological validation had to be excluded. Considering all validated localizations, [¹⁸F]FDG PET detected 12/14 tumour manifestations in the neck, 6/7 mediastinal metastases, 2/2 pulmonary metastases and 2/2 bone metastases. In two patients with elevated calcitonin levels, no diagnostic modality was able to localize a tumour. The sensitivity of [¹⁸F]FDG PET in the follow-up of MTC was 76% (95% confidence interval 53%–94%); this is encouraging. [¹⁸F]FDG PET promises to be a valuable diagnostic method, especially for the detection of lymph node metastases, surgical resection of which can result in complete remission. Received 16 September 1999 and in revised form 19 January 2000     

Role of attenuation correction for fluorine-18 fluorodeoxyglucose positron emission tomography in the primary staging of malignant lymphoma

Fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) has been shown to improve the diagnostic accuracy in the staging of malignant lymphomas, based on the metabolic signal of the lesions. This study was undertaken to determine the effect of attenuation correction in the detection of nodal and extranodal lesions in the primary staging of malignant lymphomas. Fifty-one untreated patients with either non-Hodgkin lymphoma (NHL, n=29) or Hodgkin’s disease (n=22) were retrospectively evaluated. Static FDG-PET imaging of the trunk was performed following administration of 250–350 MBq FDG. Attenuation correction was performed in all patients. Images were reconstructed iteratively with or without transmission scans. Image evaluation was performed independently by two observers, who each examined one set of images (i.e. attenuation-corrected or uncorrected). The final decision as to whether results were discordant was reached by consensus of both observers. Out of 593 evaluated lymph node regions, 187 regions of increased FDG uptake were identified by both techniques. Differences between the readers concerned mainly the anatomical assignment of lesions (n=33) or the status (benign/malignant) of individual lesions (n=24). However, direct comparison of the two sets of images demonstrated very similar lesion contrast on attenuation-corrected and non-attenuation-corrected images. Real differences could be determined only in five regions (neck, 1; mediastinum, 1; upper abdomen, 3). Thirty-seven extranodal lesions (including lung, liver, spleen, bone marrow and soft tissue) were detected by both techniques without significant differences. It is concluded that in this study, attenuation correction did not improve the diagnostic accuracy of FDG-PET in the detection of lymph node or organ involvement during the primary staging of malignant lyphomas. Of more importance seemed to be the experience of the reader regarding the classification of a lesion’s status the anatomical assignment, knowledge of physiological uptake and artefacts, and systematic and skilful examination of all regions scanned. Received 1 July and in revised form 19 September 1998     

Fluorine-18 fluorodeoxyglucose positron emission tomography in the follow-up of differentiated thyroid cancer

Whole-body fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging was performed during the follow-up of 33 patients suffering from differentiated thyroid cancer. Among them there were 26 patients with papillary and seven with follicular tumours. Primary tumour stage (pT) was pT1 in six cases, pT2 in eight cases, pT3 in three cases and pT4 in 14 cases. FDG PET was normal in 18 patients. In three patients a slightly increased metabolism was observed in the thyroid bed, assumed to be related to remnant tissue. In one case local recurrence, in ten cases lymph node metastases (one false-positive, caused by sarcoidosis) and in three cases distant metastases were found with FDG PET. In comparison with whole-body scintigraphy using iodine-131 (WBS) there were a lot of discrepancies in imaging results. Whereas three patients had distant metastases (proven with¹³¹I) and a negative FDG PET, in four cases¹³¹I-negative lymph node metastases were detectable with PET. Even in the patients with concordant staging, differences between¹³¹I and FDG were observed as to the exact lesion localization. Therefore, a coexistence of¹³¹I-positive/FDG-negative,¹³¹I-negative/FDG-positive and¹³¹I-positive/FDG-positive malignant tissue can be assumed in these patients. A higher correlation of FDG PET was observed with hexakis (2-methoxyisobutylisonitrile) technetium-99m (I) (MIBI) scintigraphy (performed in 20 cases) than with WBS. In highly differentiated tumours¹³¹I scintigraphy had a high sensitivity, whereas in poorly differentiated carcinomas FDG PET was superior. The clinical use of FDG PET can be recommended in all cases of suspected or proven recurrence and/or metastases of differentiated thyroid cancer and is particularly useful in cases with elevated serum thyroglobulin levels and negative WBS.     

Preliminary assessment of fluorine-18 fluorodeoxyglucose positron mission tomography in patients with bladder cancer

The purpose of this study was to assess the feasibility of imaging of bladder cancer with fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) scanning. We studied 12 patients with histologically proven bladder cancer who had undergone surgical procedures and/or radiotherapy. Retrograde irrigation of the urinary bladder with 1000–3710 ml saline was performed during nine of the studies. Dynamic and static PET images were obtained, and standardized uptake value images were reconstructed. FDG-PET scanning was true-positive in eight patients (66.7%), but false-negative in four (33.3%). Of 20 organs with tumor mass lesions confirmed pathologically or clinically, 16 (80%) were detected by FDG-PET scanning. FDG-PET scanning detected all of 17 distant metastatic lesions and two of three proven regional lymph node metastases. FDG-PET was also capable of differentiating viable recurrent bladder cancer from radiation-induced alterations in two patients. In conclusion, these preliminary data indicate the feasibility of FDG-PET imaging in patients with bladder cancer, although a major remaining pitfall is intense FDG accumulation in the urine. Present address: Department of Radiology, National Defense Medical College, 3-2 Namiki, Tokorozawa 359, Japan     

Comparison of fluorine-18 fluorodeoxyglucose positron emission tomography and technetium-99m methoxyisobutylisonitrile scintimammography in the detection of breast tumours

The aim of this study was to compare, in breast cancer patients, the diagnostic accuracy of positron emission tomography (PET) using fluorine-18 fluorodeoxyglucose (FDG) and scintimammography (SMM) using technetium-99m methoxyisobutylisonitrile (MIBI). A total of 20 patients (40 breasts with 22 lesions) were evaluated serially with MIBI and, on the following day, with FDG. For SMM, planar and single-photon emission tomography imaging in the prone position was performed starting at 10 min following the injection of MIBI (740 MBq). For PET, scans were acquired 45–60 min after the injection of FDG (370 MBq) and attentuation correction was performed following transmission scans. Results from SMM and PET were subsequently compared with the histopathology results. True-positive results were obtained in 12/13 primary breast cancers (mean diameter=29 mm, range 8–53 mm) with both FDG and MIBI. False-negative results were obtained in two local recurrences (diameter <9 mm) with both FDG and MIBI. In benign disease, FDG and MIBI did not localize three fibrocystic lesions, two fibroadenomas and one inflammatory lesion (true-negative), but both localized one fibroadenoma (false-positive). Collectively, the results demonstrate a sensitivity of 92%, and a specificity of 86%, for primary breast cancer regardless of whether FDG or MIBI was used. In contrast to MIBI scintigraphy, FDG PET scored the axillae correctly as either positive (metastatic disease) or negative (no axillary disease) in all 12 patients. The tumour/non-tumour ratio for MIBI was 1.97 (range 1.43–3.1). The mean standard uptake value (SUV) for FDG uptake was 2.57 (range 0.3–6.2). The diagnostic accuracy of SMM was equivalent to that of FDG PET for the detection of primary breast cancer. For the detection of in situ lymph node metastases of the axilla, FDG seems to be more sensitive than^99mTc-MIBI.     

Fluorine-18 fluorodeoxyglucose positron emission tomography and iodine-131 whole-body scintigraphy in the follow-up of differentiated thyroid cancer

Metastases of differentiated thyroid cancer may show different uptake patterns for fluorine-18 fluorodeoxyglucose and [¹³¹I]NaI. FDG positron emission tomography (PET), iodine-131 whole-body scintigraphy (¹³¹I WBS) and magnetic resonance imaging were performed in 58 unselected patients, and spiral computed tomography (CT) of the lung in 25 patients. Thirty-eight patients presented with papillary carcinomas, 15 patients with follicular carcinomas and five patients with variants of follicular carcinoma. Primary tumour stage (pT) was pT1 in 3, pT2 in 19, pT3 in 11 and pT4 in 25 cases. For the detection of metastases, FDG PET was found to have a sensitivity of 50%, ¹³¹I WBS a sensitivity of 61%, and the two methods combined a sensitivity of 86%. When FDG PET was limited to patients with elevated thyroglobulin (Tg) levels and negative ¹³¹I WBS, the sensitivity of this algorithm was 82%. Of the 21 patients with lymph node metastases, seven presented with FDG uptake but no iodine uptake. In four of them, a second FDG hot spot appeared in a lymph node metastasis of normal size. Five of the seven patients underwent surgery. None of the eight patients with pulmonary metastases smaller than 1 cm exhibited FDG uptake, while five of them had iodine uptake. All had positive results on spiral CT. In conclusion, FDG PET cannot be substituted for ¹³¹I WBS. If the Tg level is elevated and ¹³¹I WBS is negative, FDG PET can be used to detect lymph node metastases and complements anatomical imaging. A spiral CT of the lung is useful to exclude pulmonary metastases before planning a dissection of iodine-negative lymph node metastases. Received 2 May and in revised form 8 July 1997     

Cerebral interregional correlations of associative language processing: a positron emission tomography activation study using fluorine-18 fluorodeoxyglucose

Even though there have been numerous positron emission tomography (PET) activation studies on the perfusional and metabolic bases of language processing, little is known about the intracerebral functional network of language and cognitive processes. It was the aim of this study to investigate the cerebral interregional correlations during voluntary word association versus word repetition in healthy subjects to gain insight into the functional connectivity of associative speech processing. Due to individual variability in functional anatomy, the study protocol was designed as an averaged single-subject study. Eight healthy volunteers performed a verbal association task during fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) PET scanning. Two different tasks were performed in randomized order: (a) word repetition (after auditory presentation of nouns) as a control condition, and (b) word association (after auditory presentation of nouns) as a specific semantic activation. The regional metabolic rate of glucose (rMRGlu) was calculated after brain regionalization [112 regions of interest on individual 3D flash magnetic resonance imaging (MRI)] and PET/MRI realignment. Statistical analysis was performed for comparison of association and repetition and for calculation of interregional correlation coefficients during both tasks. Compared with word repetition, word association was associated with significant increases in rMRGlu in the left prefrontal cortex, the left frontal operculum (Broca’s area) and the left insula, indicating involvement of these areas in associative language processing. Decreased rMRGlu was found in the left posterior cingulum during word association. During word repetition, highly significant negative correlations were found between the left prefrontal cortex, the contralateral cortex areas and the ipsilateral posterior cingulum. These negative correlations were almost completely eliminated during the association task, suggesting a functional decoupling of the strict intercorrelation pattern. Received 16 March and in revised form 9 July 1998     

Fluorine-18-fluorodeoxyglucose positron emission tomography for preoperative parathyroid imaging in primary hyperparathyroidism

Fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging was performed in seven consecutive patients with primary hyperparathyroidism to preoperatively locate parathyroid adenomas. Foci of FDG accumulation corresponding to abnormal parathyroid tissue were observed in two out of nine surgically excised parathyroid adenomas. It was concluded that FDG PET imaging demonstrated a too low sensitivity for systematic preoperative detection and localization of parathyroid glands causing primary hyperparathyroidism.     

Early response monitoring in malignant lymphoma using fluorine-18 fluorodeoxyglucose single-photon emission tomography

Metabolic response monitoring early during chemotherapy may have a major impact on clinical management of patients with malignant lymphoma. In two patients with non-Hodgkin's lymphoma fluorine-18 fluorodeoxyglucose (IgFDG) single-photon emission tomography (SPET) studies were performed during the first two chemotherapeutic cycles. Persisting uptake predicted treatment failure whereas a sharp reduction of ¹⁸FDG uptake was demonstrated in the case of a responsive tumour. Qualitative analysis of conventional ¹⁸FDG imaging may thus serve to identify patients with a non-responding tumour. The potential of this technique in the determination of the initial response remains to be established. Imaging with ¹⁸FDG and SPET appears promising as a more easily available methodology than ¹⁸FDG positron emission tomography.     

Fluorine-18 fluorodeoxyglucose positron emission tomography in thyroid cancer: results of a multicentre study

n =222) and the group with negative radioiodine scan (n=166), respectively. Specificity was 90% in the whole patient group. Sensitivity and specificity of WBS were 50% and 99%, respectively. When the results of FDG-PET and WBS were considered in combination, tumour tissue was missed in only 7%. Sensitivity and specificity of MIBI/Tl were 53% and 92%, respectively (n=117). We conclude that FDG-PET is a sensitive method in the follow-up of thyroid cancer which should be considered in all patients suffering from differentiated thyroid cancer with suspected recurrence and/or metastases, and particularly in those with elevated thyroglobulin values and negative WBS. Received 4 May and in revised form 11 June 1999     

Use of fluorine-18 fluorodeoxyglucose positron emission tomography in the detection of silent metastases from malignant melanoma

Correct staging is crucial for the management and prognosis of patients with malignant melanoma. The aim of this prospective study was to compare staging by whole-body positron emission tomography using fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) with staging by conventional methods. Thirty-eight patients with malignant melanoma of clinical stage II (local recurrence, in-transit and regional lymph node metastases) or III (metastases to other sites than in stage II) were included in the study. The results of the PET scans were compared with those obtained by clinical examination, computed tomography, ultrasound, radiography, and liver function tests and histology or clinical follow-up. With ¹⁸F-FDG PET we found for all foci a sensitivity of 97% and a specificity of 56%, compared with 62% and 22%, respectively, when using routine methods. For intra-abdominal foci, the sensitivity and specificity were 100% for both ¹⁸F-FDG PET and routine methods. Corresponding figures for pulmonary/intrathoracic foci were 100% and 33%, respectively. Of the patients included in this study, 34% would not have been staged correctly by conventional methods alone. We conclude from this study that ¹⁸F-FDG PET is a sensitive method superior to conventional methods for detecting widespread metastases from malignant melanoma. Mutilating surgery of no benefit can thereby be avoided. ¹⁸F-FDG PET is useful as a supplement to clinical examination in melanoma staging. Received 26 May and in revised form 20 September 1999     

A comparative study of thallium-201 SPET, carbon-11 methionine PET and fluorine-18 fluorodeoxyglucose PET for the differentiation of astrocytic tumours

Thallium-201, carbon-11 methionine (MET) and fluorine-18 fluorodeoxyglucose (FDG) have all been used to assess brain tumours. The aim of this study was to determine which of these tracers are of use for evaluating the histological grade and the extent of astrocytoma. ²⁰¹Tl single-photon emission tomography (SPET), MET positron emission tomography (PET) and FDG PET were all performed in 23 patients (13 men, 10 women) with newly diagnosed astrocytic tumours [seven with astrocytoma (grade II), ten with anaplastic astrocytoma (grade III) and six with glioblastoma (grade IV)]. The ²⁰¹Tl uptake of the tumours was evaluated by a lesion-to-normal region count ratio. Both MET and FDG uptake of the tumours was evaluated by a semiquantitative analysis using the standardized uptake value. ²⁰¹Tl uptake was found to increase in rank order with histological grade and was significantly different among the three groups (grade II: 1.51±0.36; grade III: 2.58±1.50; grade IV: 7.65±3.84). MET uptake in grade II (1.49±0.44) was also significantly lower than that in both grade III (3.29±1.44) and grade IV (3.20±0.92). FDG uptake was not significantly different among the three groups (grade II: 2.90±0.45; grade III: 3.86±1.56; grade IV: 3.57±0.83). No significant correlation was observed between ²⁰¹Tl uptake and either MET uptake or FDG uptake. In most patients, the extent of the increased MET uptake was the largest while that of the increased FDG uptake was the smallest. In patients with positive ²⁰¹Tl uptake, the extent of the ²⁰¹Tl uptake was equal to or smaller than that of gadolinium enhancement. For evaluation of histological grade of astrocytic tumours. ²⁰¹Tl is therefore considered to be useful though the ²⁰¹Tl uptake in some grade III astrocytomas was not different from that in grade II astrocytomas. MET was found to be highly useful for detecting astrocytomas, for differentiating between benign and malignant astrocytomas, and for evaluating the extent of astrocytomas; however, it was not sufficiently useful permit evaluation of the histological grade. FDG was not found to be useful either for evaluating the histological grade or for differentiating between benign and malignant astrocytomas. Received 10 March and in revised form 11 May 1998     

Use of fluorine-18 fluorodeoxyglucose positron emission tomography in the detection of thymoma: A preliminary report

Thymomas are lacking in malignant cytological features. Their staging is defined by the invasiveness of the tumour. This study aimed to analyse the uptake patterns of fluorine-18 fluorodeoxyglucose (FDG) in thymomas of different stages. FDG positron emission tomography (PET) scan was performed in 12 patients suspected of having thymoma and in nine controls. Qualitative visual interpretation was used to detect the foci with FDG uptake higher than that of normal mediastinum. Tumour/lung ratio (TLR) was calculated from the counts of ROIs over the mass and over comparable normal lung tissue in thymoma patients. Mediastinum/lung ratio (MLR) was calculated from the counts of ROIs over the anterior mediastinum and lung in controls. The PET scan patterns of distribution of foci with FDG uptake and TLRs were correlated with the computed tomography (CT) or magnetic resonance imaging (MRI) findings, and staging of the thymomas. Thymectomy was performed in ten patients and thoracoscopy was done in two patients. The results revealed ten thymomas (two stage I tumours, two stage II, four stage III and two stage IV, according to the Masaoka classification), and two cases of thymic hyperplasia associated with myasthenia gravis. Myasthenia gravis was also noted in four thymoma patients. FDG studies showed (a) diffuse uptake in the widened anterior mediastinum in patients with thymic hyperplasia, (b) confined focal FDG uptake in the non-invasive or less invasive, stage I and II thymomas, and (c) multiple discrete foci of FDG uptake in the mediastinum and thoracic structures in stage III and IV advanced invasive thymomas. The thymomas had the highest TLRs, followed by the TLRs of thymic hyperplasia and the MLRs of control subjects (P <0.005). No significant difference was found between thymomas in different stages or between thymomas with and thymomas without myasthenia gravis. In comparison with CT and/or MRI, FDG-PET detected more lesions in patients with invasive thymomas and downgraded the staging of thymoma in four patients. Our preliminary results suggest that FDG-PET is useful in the assessment of the invasiveness of thymomas, and may have the potential to differentiate thymomas from thymic hyperplasia.     

Standardized uptake values of fluorine-18 fluorodeoxyglucose: the value of different normalization orocedures

While the evident advantages of absolute metabolic rate determinations cannot be equalled by static image analysis of fluorine-18 fluorodeoxyglucose positron emission tomographic (FDG PET) studies, various algorithms for the normalization of static FDG uptake values have been proposed. This study was performed to compare different normalization procedures in terms of dependency on individual patient characteristics. Standardized FDG uptake values (SUVs) were calculated for liver and lung tissue in 126 patients studied with wholebody FDG PET. Uptake values were normalized for total body weight, lean body mass and body surface area. Ranges, means, medians, standard deviations and variation coefficients of these SUV parameters were calculated and their interdependency with total body weight, lean body mass, body surface area, patient height and blood sugar levels was calculated by means of regression analysis. Standardized FDG uptake values normalized for body surface area were clearly superior to SUV parameters normalized. for total body weight or lean body mass. Variation and correlation coefficients of body surface area-normalized uptake values were minimal when compared with SUV parameters derived from the other normalization procedures. Normalization for total body weight resulted in uptake values still dependent on body weight and blood sugar levels, while normalization for lean body mass did not eliminate the positive correlation with lean body mass and patient height. It is concluded that normalization of FDG uptake values for body surface area is less dependent on the individual patient characteristics than are FDG uptake values normalized for other parameters, and therefore appears to be preferable for FDG PET studies in oncology.     

Fluorine-18 fluorodeoxyglucose positron mission tomography in the differential diagnosis of pancreatic carcinoma: a report of 106 cases

The aim of this study was to evaluate fluorine-18 fluorodeoxyglucose positron emission tomography ([¹⁸F]FDG PET) as a tool for the differential diagnosis of pancreatic carcinoma while taking into account serum glucose level. A group of 106 patients with unclear pancreatic masses were recruited for the study. PET was performed following intravenous administration of an average of 190 MBq [¹⁸F]FDG. Focally increased glucose utilisation was used as the criterion of malignancy. In addition, the \ldstandardised uptake value\rd (SUV) was determined 45 min after injection. Carcinoma of the pancreas was demonstrated histologically in 74 cases, and chronic pancreatitis in 32 cases. Employing visual evaluation, 63 of the 74 (85%) pancreatic carcinomas were identified by PET. In 27 of the 32 cases (84%) of chronic pancreatitis il was possible to exclude malignancy. False-negative results (n=11) were obtained mostly in patients with raised serum glucose levels (10 out of 11), and false-positives (n=5) in patients with inflammatory processes of the pancreas. Thus PET showed an overall sensitivity of 85%, a specificity of 84%, a negative predictive value of 71%, and a positive predictive value of 93%. In a subgroup of patients with normal serum glucose levels (n=72), the results were 98%, 84%, 96% and 93%, respectively. Quantitative assessment yielded a mean SUV of 6.4\+-3.6 for pancreatic carcinoma as against a value of 3.6\+-1.7 for chronic pancreatitis (P\s<0.001), without increasing the diagnostic accuracy. This shows PET to be of value in assessing unclear pancreatic masses. The diagnostic accuracy of PET examinations is very dependent on serum glucose levels.