Cold tuberculous abscess identified by FDG PET

We report FDG PET of two cases of cold abscess due to Mycobacterium tuberculosis. Case 1 had colon cancer; FDG PET showed high FDG uptake in the colon lesion and low uptake in the inguinal lesion. The latter was a tuberculous cold abscess confirmed by CT/MRI and biopsy. Case 2 received radiotherapy for lung cancer and presented with suspected vertebral metastasis. Further studies revealed tuberculosis of the vertebra and a tuberculous cold abscess in the iliopsoas muscle. FDG PET showed moderate uptake in the third lumbar spine and low uptake in the abscess center of iliopsoas lesion. Both tuberculous cold abscesses showed moderate FDG uptake in the capsule and low uptake in the center. These features are unique compared with non-tuberculous abscess and typical tuberculosis lesions, which are characterized by high FDG uptake. Pathologically, tuberculous cold abscess is not accompanied by active inflammatory reaction. Our findings suggested that the FDG uptake by tuberculous lesion varies according to the grade of inflammatory activity. The new diagnostic features of tuberculous cold abscess may be useful in the evaluation of such lesions by FDG PET.     

<Superscript>18</Superscript>F-choline in experimental soft tissue infection assessed with autoradiography and high-resolution PET

For each oncological tracer it is important to know the uptake in non-tumorous lesions. The purpose of this study was to measure the accumulation of fluorine-18 choline (FCH), a promising agent for the evaluation of certain tumour types, in infectious tissue. Unilateral thigh muscle abscesses were induced in five rats by intramuscular injection of 0.1 ml of a bacterial suspension (Staphylococcus aureus, 1.2×10⁹ CFU/ml). In all animals, FCH accumulation was measured with high-resolution positron emission tomography (PET) on day 6. Autoradiography of the abscess and ipsilateral healthy muscle was performed on day 7 (three animals) and day 11 (two animals) and correlated with histology. In addition, ¹⁸F-fluorodeoxyglucose (FDG) PET was performed on day 5. Increased FCH uptake was noted in specific layers of the abscess wall which contained an infiltrate of mainly granulocytes on day 7 and mainly macrophages on day 11. The autoradiographic standardised uptake values in the most active part of the abscess wall were 2.99 on day 7 (n=3) and 4.05 on day 11 (n=2). In healthy muscle the corresponding values were 0.99 and 0.64. The abscesses were clearly visualised on the FCH and FDG PET images. In conclusion, this study demonstrated avid FCH accumulation in inflammatory tissue, which limits the specificity of FCH for tumour detection. Future studies are now needed to determine the degree of this limitation in human cancer patients.     

Fluorine-18 deoxyglucose PET for assessment of viable myocardium in perfusion defects in 99mTc-MIBI SPET: a comparative study in patients with coronary artery disease

Extent and frequency of viable tissue in myocardial segments yielding a perfusion defect on technetium-99m methoxyisobutylisonitrile (^99mTc-MIBI), single photon emission tomography (SPET) at rest was prospectively investigated with 2-¹⁸F-2-deoxyglucose (¹⁸FDG) positron emission tomography (PET) in 46 patients with chronic coronary artery disease (CAD). Of these, 43 had a history of old myocardial infarction. For comparative visual and quantitative evaluation of identical anatomical slices, PET image files were converted into the SPET file structure and into the same matrix size. SPET and PET images were documented and visually (9 segments/patient) or semiquantitatively evaluated by a target-like polar map. Relative perfusion was expressed in percentage of peak ^99mTc-MIBI uptake. Sample ¹⁸FDG uptake was related to the ¹⁸FDG uptake in the area of such maximal perfusion (¹⁸FDG uptake was 100% at the 100% ^99mTc-MIBI uptake area). Of 414 segments, 167 (40%) revealed a resting perfusion defect. ¹⁸FDG uptake was present in 38 (23%) of the defects, while another 40 (24%) segments yielded ¹⁸FDG uptake in the periphery of the defect. When grouped according to the degree of ^99mTc-MIBI uptake-reduction (in percentage of peak activity), 80% of severe defects (30% of peak uptake), 48% of moderate (31%–50% of peak uptake) and 31% of mild (>50% of peak uptake) defects were considered as non-viable on the basis of ¹⁸FDG uptake. Complete viability was found in none of the severe defects in contrast to 29% of moderate and 35% of mild perfusion defects. From these data we conclude that ^99mTc-MIBI uptake as a myocardial perfusion marker underestimates myocardial viability in patients with chronic CAD and after myocardial infarction. Nevertheless, only moderate reductions of ^99mTc-MIBI uptake seem to imply a greater likelihood for viability. Comparative analysis of metabolism and flow is possible with different tomographic systems and is valuable for clinical evaluation of the cardiac patient. Offprint requests to: C. AltehoeferThis paper presents in part results of the doctoral thesis of C. Feinendegen and was supported in part by the EEC Concerted Action on PET in Cardiology.It is dedicated to Prof. L.E. Feinendegen, Jülich/Düsseldorf on the occasion of his 65th birthday.     

18F-FDG PET in malignant lymphoma: significance of positive findings

Purpose The aim of this study was to evaluate the significance of increased uptake of ¹⁸F-fluorodeoxyglucose (FDG) in patients with malignant lymphoma (ML) studied by positron emission tomography (PET).Methods A total of 1,120 consecutive scans carried out in 848 patients were reviewed; all patients had a diagnosis of ML [574 non-Hodgkins lymphoma (NHL) and 274 Hodgkins disease (HD)] and were studied at completion of therapy, for suspected recurrence or during follow-up. PET was carried out after intravenous injection of 370 MBq of ¹⁸F-FDG; images were recorded after 60–90 min. Patients were selected whose reports indicated areas of increased FDG uptake. PET findings were considered positive for lymphomatous localisation when uptake occurred at sites of previous disease, in asymmetrical lymph nodes or in nodes unlikely to be affected by inflammation (mediastinal, except for hilar, and abdominal). PET findings were adjudged negative for neoplastic localisations in the following instances: physiological uptake (urinary, muscular, thymic or gastrointestinal in patients without MALT), symmetrical nodal uptake, uptake in lesions unrelated to lymphoma that had already been identified by other imaging methods at the time of PET scan, uptake at sites atypical for lymphoma, very low uptake and non-focal uptake. PET findings were compared with the results of other diagnostic procedures (including CT and ultrasound), biopsy findings and follow-up data.Results Overall, 354 scans (in 256 patients) showed increased FDG uptake (244 scans in NHL and 110 in HD): in 286 cases, FDG uptake was considered pathological and indicative of ML, in 41 cases the findings were described as uncertain or equivocal and in 37 cases, FDG uptake was considered unrelated to ML (in ten scans, concurrent findings of abnormal FDG uptake attributed to ML and uptake assigned to other causes were obtained) . Of the 286 patients with positive PET findings, 274 (95.8%) were found to have residual or recurrent ML (i.e. true positives). Four of the 41 patients with inconclusive findings turned out to have ML, while in 13 patients, pathological processes other than ML could be identified as the cause of FDG uptake. ML was excluded in all patients with findings reported as non-pathological (100% true-negative rate). Therefore, the false-positive rate in our series was about 5%. The main cause of increased FDG uptake mimicking ML was inflammation.Conclusion Our data confirm that ¹⁸F-FDG-PET has very high but not absolute specificity for ML. As already suggested, increased FDG uptake may also be observed in patients without active disease; in most cases, however, non-pathological FDG accumulation is properly identified. Less frequently, inconclusive scans are encountered; these cases are usually caused by inflammation, which subsequently resolves.     

Lymphadenopathy by Scrub Typhus Mimicking Metastasis on FDG PET/CT in a Patient with a History of Breast Cancer

We report the case of a 60-year-old woman with left-sided breast cancer who showed lymphadenopathy mimicking metastatic lesions. She underwent surveillance ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) after treatment. PET/CT demonstrated multiple lymphadenopathies with increased FDG uptake, most notably in the right axilla. She had an eschar on the right axillary area, and her serologic test was positive for anti-Orientia tsutsugamushi IgM antibody. Ten months after the treatment, follow-up FDG PET/CT and ultrasonography showed improvement in generalized lymphadenopathy.     

11C-methionine PET as a prognostic marker in patients with glioma: comparison with 18F-FDG PET

Purpose The purpose of this study was to compare the prognostic value of ¹¹C-methionine (MET) and ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in glioma patients.Methods The study population comprised 47 patients with gliomas (19 glioblastoma, 28 others). Pretreatment magnetic resonance imaging, MET PET and FDG PET were performed within a time interval of 2 weeks in all patients. The uptake ratio and standard uptake values were calculated. Univariate and multivariate analyses were done to determine significant prognostic factors. Ki-67 index was measured by immunohistochemical staining, and compared with FDG and MET uptake in glioma.Results Among the several clinicopathological prognostic factors, tumour pathology (glioblastoma or not), age (60 or <60 years), Karnofsky performance status (KPS) (70 or <70) and MET PET (higher uptake or not compared with normal cortex) were found to be significant predictors by univariate analysis. In multivariate analysis, tumour pathology, KPS and MET PET were identified as significant independent predictors. The Ki-67 proliferation index was significantly correlated with MET uptake (r=0.64), but not with FDG uptake.Conclusion Compared with FDG PET in glioma, MET PET was an independent significant prognostic factor and MET uptake was correlated with cellular proliferation. MET PET may be a useful biological prognostic marker in glioma patients.     

Correlation of <Superscript>18</Superscript>F-FLT and <Superscript>18</Superscript>F-FDG uptake on PET with Ki-67 immunohistochemistry in non-small cell lung cancer

Purpose The nucleoside analogue 3′-deoxy-3′-¹⁸F-fluorothymidine (FLT) has recently been introduced for imaging cell proliferation with positron emission tomography (PET). We prospectively evaluated whether FLT uptake reflects proliferative activity as indicated by the Ki-67 index in non-small cell lung cancer (NSCLC), in comparison with 2-deoxy-2-¹⁸F-fluoro-D-glucose (FDG). Methods A total of 18 patients with newly diagnosed NSCLC were examined with both FLT PET and FDG PET. PET imaging was performed at 60 min after each radiotracer injection. Tumour lesions were identified as areas of focally increased uptake, exceeding background uptake in the lungs. For semi-quantitative analysis, the maximum standardised uptake value (SUV) was calculated. Proliferative activity as indicated by the Ki-67 index was estimated in tissue specimens. Immunohistochemical findings were correlated with SUVs. Results The sensitivity of FLT and FDG PET for the detection of lung cancer was 72% and 89%, respectively. Four of the five false-negative FLT PET findings occurred in bronchiolo-alveolar carcinoma. The mean FLT SUV was significantly lower than the mean FDG SUV. A significant correlation was observed between FLT SUV and Ki-67 index (r = 0.77; p < 0.0002) and for FDG SUV (r = 0.81; p < 0.0001). Conclusion The results of this preliminary study suggest that, compared with FDG, FLT may be less sensitive for primary staging in patients with NSCLC. Although FLT uptake correlated significantly with proliferative activity in NSCLC, the correlation was not better than that for FDG uptake.     

<Superscript>11</Superscript>C-acetate PET imaging of lung cancer: comparison with <Superscript>18</Superscript>F-FDG PET and <Superscript>99m</Superscript>Tc-MIBI SPET

Recently carbon-11 acetate (AC) positron emission tomography (PET) has been reported to be of clinical value for the diagnosis of cancer that is negative on fluorine-18 fluorodeoxyglucoce (FDG) PET. We investigated the uptake of AC in lung cancer to determine whether this tracer is of potential value for tumour detection and characterisation, and to compare AC PET imaging with FDG PET and technetium-99m sestamibi (MIBI) single-photon emission tomography (SPET). Twenty-three patients with 25 lung cancers underwent AC and FDG PET. Twenty of 23 patients were also investigated with MIBI SPET. Dynamic images were acquired for 26 min after the injection of 555 MBq of AC. Standardised uptake values (SUVs) and/or tumour to non-tumour activity ratios (T/N) for each tumour were investigated at 10–20 min after AC administration, 40–60 min after administration of 185 MBq FDG and 15–45 min after administration of 555 MBq MIBI. Twenty lung cancers were resected surgically, and the degree of tracer uptake in the primary lesion was correlated with histopathological features (cell dedifferentiation and aggressiveness) and prognosis. Rapid uptake of AC followed by extremely slow clearance was observed. For the purpose of tumour identification, AC PET was inferior to FDG PET in 8 of 25 (32%) lung cancers, and the T/N of AC was lower than that of FDG. However, AC PET was superior to FDG PET in the identification of a slow-growing tumour (bronchiolo-alveolar carcinoma). There was a positive correlation between AC uptake (T/N) and MIBI uptake (T/N) (r=0.799, P<0.0001). A positive correlation was not observed between either AC or MIBI uptake and the degree of cell dedifferentiation in lung adenocarcinomas, whereas FDG uptake did correlate with the degree of cell dedifferentiation. In lung adenocarcinoma, there was a weak correlation between aggressiveness and FDG uptake, but no correlation was evident for AC and MIBI. In addition, a positive correlation was not observed between AC or MIBI uptake and postoperative recurrence in lung adenocarcinoma, whereas FDG uptake did correlate with postoperative recurrence. Thus, the greater the FDG uptake, the higher the malignant grade. In conclusion, for the purpose of tumour identification, AC PET was inferior to FDG PET but superior to MIBI SPET. Neither AC nor MIBI uptake reflects the malignant grade in lung adenocarcinoma, whereas FDG uptake does. AC PET is less diagnostically informative than FDG PET in patients with lung cancer. However, AC PET may play a complementary role in the identification of low-grade malignancies that are not FDG avid.     

Detection of gastric cancer using <Superscript>18</Superscript>F-FLT PET: comparison with <Superscript>18</Superscript>F-FDG PET

Purpose  We prospectively investigated the feasibility of 3′-deoxy-3′-¹⁸F-fluorothymidine (FLT) positron emission tomography (PET) for the detection of gastric cancer, in comparison with 2-deoxy-2-¹⁸F-fluoro-d-glucose (FDG) PET, and determined the degree of correlation between the two radiotracers and proliferative activity as indicated by Ki-67 index. Methods  A total of 21 patients with newly diagnosed advanced gastric cancer were examined with FLT PET and FDG PET. Tumour lesions were identified as areas of focally increased uptake, exceeding that of surrounding normal tissue. For semiquantitative analysis, the maximal standardized uptake value (SUV) was calculated. Results  For detection of advanced gastric cancer, the sensitivities of FLT PET and FDG PET were 95.2% and 95.0%, respectively. The mean (±SD) SUV for FLT (7.0 ± 3.3) was significantly lower than that for FDG (9.4 ± 6.3 p < 0.05). The mean FLT SUV and FDG SUV in nonintestinal tumours were higher than in intestinal tumours, although the difference was not statistically significant. The mean (±SD) FLT SUV in poorly differentiated tumours (8.5 ± 3.5) was significantly higher than that in well and moderately differentiated tumours (5.3 ± 2.1; p < 0.04). The mean FDG SUV in poorly differentiated tumours was higher than in well and moderately differentiated tumours, although the difference was not statistically significant. There was no significant correlation between Ki-67 index and either FLT SUV or FDG SUV. Conclusion  FLT PET showed as high a sensitivity as FDG PET for the detection of gastric cancer, although uptake of FLT in gastric cancer was significantly lower than that of FDG.     

Uptake of 18F-fluorocholine, 18F-fluoro-ethyl-L-tyrosine and 18F-fluoro-2-deoxyglucose in F98 gliomas in the rat

Introduction The positron emission tomography (PET) tracers ¹⁸F-fluoro-ethyl-L-tyrosine (FET), ¹⁸F-fluorocholine (N,N-dimethyl-N-[¹⁸F]fluoromethyl-2-hydroxyethylammonium (FCH]) and ¹⁸F-fluoro-2-deoxyglucose (FDG) are used in the diagnosis of brain tumours. The aim of this study was threefold: (a) to assess the uptake of the different tracers in the F98 rat glioma, (b) to evaluate the impact of blood-brain barrier (BBB) disruption and microvessel density (MVD) on tracer uptake and (c) to compare the uptake in the tumours to that in the radiation injuries (induced by proton irradiation of healthy rats) of our previous study.Methods F98 gliomas were induced in 26 rats. The uptake of FET, FCH and FDG was measured using autoradiography and correlated with histology, disruption of the BBB and MVD.Results The mean FET, FCH and FDG standardised uptake values (SUVs) in the tumour and the contralateral normal cortex (in parentheses) were 4.19±0.86 (1.32±0.26), 2.98±0.58 (0.51±0.11) and 11.02±3.84 (4.76±1.77) respectively. MVD was significantly correlated only with FCH uptake. There was a trend towards a negative correlation between the degree of BBB disruption and FCH uptake and a trend towards a positive correlation with FET uptake. The ratio of the uptake in tumours to that in the radiation injuries was 1.97 (FCH), 2.71 (FET) and 2.37 (FDG).Conclusion MVD displayed a significant effect only on FCH uptake. The degree of BBB disruption seems to affect the accumulation of FET and FCH, but not FDG. Mean tumour uptake for all tracers was significantly higher than the accumulation in radiation injuries.     

Perirenal 18F-FDG Uptake in a Patient with a Pheochromocytoma

Increased ¹⁸F-fluorodeoxyglucose (FDG) uptake of brown fat on ¹⁸F-FDG positron emission tomography (PET) originating from physiological activation is a common incidental finding and is usually located in the neck, shoulder, and supraclavicular areas. We present a case of an incidental pheochromocytoma showing diffusely increased ¹⁸F-FDG uptake in bilateral perirenal fat tissue as well as supraclavicular and paravertebral fat tissue on ¹⁸F-FDG PET/CT. The patient had no clinical symptoms except hypertension, and a pheochromocytoma was confirmed in a postsurgical specimen. A pheochromocytoma should be considered a cause in cases of increased ¹⁸F-FDG uptake of perirenal brown fat.     

18FDG uptake associated with CT density on PET/CT in lungs with and without chronic interstitial lung diseases

Objective  The dependent-density of computed tomography (CT) images of positron emission tomography (PET)/CT is sometimes difficult to distinguish from chronic interstitial lung disease (ILD) when it accompanies increased ¹⁸F-fluorodeoxy-d-glucose (¹⁸FDG) uptake. Though the possible utility of ¹⁸FDG-PET for the diagnosis of active ILD has been reported, the clinical relevance of mild lung ¹⁸FDG uptake in ILD cases without signs and symptoms suggesting acute progression has not been described. This study aimed to test relationships between ¹⁸FDG uptake and lung density on CT using PET/CT in patients with normal lung as well as clinically stable chronic ILD. Methods  Thirty-six patients with normal lungs (controls) and 28 patients with chronic ILD (ILD cases) without acute exacerbation were retrospectively selected from ¹⁸FDG-PET/CT scans performed in examination of malignant neoplasms. Elliptical regions of interest (ROIs) were placed on the lung. The relationships between CT density and ¹⁸FDG uptake between the control and ILD cases were tested. Results  The CT density and ¹⁸FDG uptake had a linear correlation in both the controls and the ILD cases without a difference in their regression slopes, and they were overlapped between the controls and the ILD cases with higher mean values in the ILD cases. Conclusions  Lung ¹⁸FDG uptake was considered to reflect a gravity-dependent tissue density in the normal lung. Though the lung ¹⁸FDG uptake as well as the CT density tended to be higher in chronic ILD patients, it may be difficult to distinguish them in normal dependent regions from those related to chronic ILD in some cases.     

Osteonecrosis Mimicking Bone Metastasis in Femoral Head on 18F-FDG PET/CT: A Case Report

A 77-year-old woman underwent chemotherapy, radiotherapy, and brachytherapy for cervical cancer 9 years ago. On a follow-up ¹⁸F-fluorodeoxyglucose (FDG) PET/CT image, focal FDG uptake was noted in a focal osteolytic lesion in the right femoral head. During magnetic resonance imaging, this lesion showed subchondral dark-signal-intensity rim on T1-weighted image and double line sign on T2-weighted image, suggestive of osteonecrosis. The lesion was pathologically confirmed as osteonecrosis after surgery. This case demonstrates that osteonecrosis of the femoral head may demonstrate focal FDG uptake mimicking bone metastasis.     

Temporal relation between temperature change and FDG uptake in brown adipose tissue

Objectives It has been reported that the prevalence of ¹⁸F fluorodeoxyglucose (FDG) uptake in brown adipose tissue (BAT) is related to outdoor temperature, i.e., more frequent during the colder periods of the year. The purpose of this study was to assess the temporal relationship between BAT FDG uptake and temperature. We correlated the prevalence of BAT with average temperatures (divided into five temperature ranges) of seven different durations. Methods One thousand four hundred ninety-five consecutive FDG Positron emission tomography (PET) studies in 1,159 patients (566 male and 593 female, mean age = 60.4 years) were retrospectively reviewed. FDG uptake with distinct patterns compatible with BAT was identified by a consensus of two readers. The local daily average temperature from January 2000 to November 2003 (beginning 60 days before the date of first PET scan) were obtained, and 2-, 3-, 7-, 14-, 30-, and 60-day average temperatures before the date of a PET study were calculated. The prevalence of BAT FDG uptake was correlated with these various average temperatures. Results The daily, 2-day, 3-day, and 7-day average temperature had an inverse relation with the prevalence of BAT, i.e., the lower the temperature, the higher prevalence of BAT. When the temperature was averaged over 14 days or longer, this inverse relationship between the temperature and the prevalence of BAT was no longer preserved. Conclusions Our data suggest that increased FDG uptake in BAT occurs more often as an acute response to cold weather (1–7 days) rather than to prolonged periods of average cold weather.     

Efficiency of 18F-FDG and 99mTc-depreotide SPECT in the diagnosis of malignancy of solitary pulmonary nodules

Purpose The purpose of the study was to compare ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) and ^99mTc-depreotide single-photon emission computed tomography (SPECT) in the diagnosis of malignancy of solitary pulmonary nodules (SPNs).Methods Twenty-eight patients without any history of cancer and presenting an SPN (0.8–3 cm in size) underwent FDG PET and depreotide SPECT. Depreotide SPECT and FDG PET were performed on a double-head gamma camera and a dedicated PET scanner respectively. Twenty-five out of 28 lesions were removed by thoracotomy or assessed by biopsy (n=1) and histologically examined. A strategy of serial CT scanning was adopted in the three remaining patients.Results Histological findings revealed 18 malignant nodules and seven benign lesions. Stability over a 2-year period indicated a benign process in the remaining three cases. Both techniques yielded true positive results in 15 of the 18 cancers. FDG PET identified two additional adenocarcinomas not detected by depreotide SPECT. A carcinoid tumour not visualised on FDG PET was identified by depreotide SPECT. Seven of the ten benign lesions did not reveal tracer uptake on either depreotide SPECT or FDG PET. Both techniques showed false positive results for the same two lesions. One more false positive was seen on FDG PET. FDG PET and depreotide SPECT had a sensitivity of 94.4% and 88.9% respectively; this difference was not significant. In our experience, depreotide SPECT and FDG PET are equally sensitive (92.3%) for large (>1.5 cm) and equally specific (85.7%) for small (up to 1.5 cm) SPNs suspicious for malignancy.Conclusion This study showed ¹⁸F-FDG PET to be more sensitive than ^99mTc-depreotide SPECT in the diagnosis of malignancy of SPNs. However, the combination of both techniques may provide additional accuracy.     

A case of septic pulmonary embolism associated with renal abscess mimicking pulmonary metastases of renal malignancy

We report the case of a 46-year-old woman with acute febrile symptom who had multiple pulmonary nodules and a renal mass. She underwent ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) to find a hidden malignancy and the cause of her fever. FDG PET/CT images demonstrated a renal mass and multiple lung nodules with intense FDG uptake, which was suspicious of a renal malignancy with multiple pulmonary metastatic lesions. CT-guided biopsies of the pulmonary and renal lesions only showed chronic inflammatory infiltrates without evidence of malignancy. She was diagnosed with septic pulmonary embolism from a renal abscess. One month after antibiotic treatment, the follow-up chest and abdomen CT showed improvement of the lung and renal lesions. This is the first case demonstrating the FDG PET/CT finding of septic pulmonary embolism associated with renal abscess in the published literature.     

90Y microsphere treatment of unresectable liver metastases: changes in 18F-FDG uptake and tumour size on PET/CT

Purpose The intra-arterial administration of ⁹⁰Y microspheres is a new palliative treatment option for unresectable liver metastases. The aim of this study was to quantitatively assess changes in FDG uptake and tumour size following ⁹⁰Y microsphere treatment (SIR-Spheres) using ¹⁸F-fluorodeoxyglucose (FDG) PET/CT imaging.Methods Five patients with unresectable liver metastases who had failed multiple prior chemotherapy regimens received seven ⁹⁰Y microsphere treatments to a single liver lobe. All patients underwent a baseline PET/CT scan prior to treatment, as well as up to four follow-up PET/CT scans. The tumour area of 30 liver metastases was measured on CT and the FDG uptake was semiquantitatively assessed by calculation of standardised uptake values (SUVs). A total of 18 FDG-PET/CT scans were performed.Results The SUVs in the 30 treated liver metastases decreased from 6.5±2.3 at baseline to 4.2±1.8 after the first follow-up PET/CT scan (p=0.001). In contrast, the SUVs of untreated metastases increased slightly from 7.2±2.3 to 8.0±0.8. There was no difference in FDG uptake in treated versus untreated normal liver tissue. Using a previously defined threshold of 20% decrease in SUV from baseline to determine response, 20 out of 30 liver metastases were considered to have responded at the first follow-up PET/CT scan approximately 1 month after treatment. In these metastases, the SUV decreased by 47±12%, compared with a slight increase by 5.9±19% in ten non-responding metastases (p=0.0001). The changes in tumour size did not correlate with changes in FDG uptake. On the first follow-up PET/CT scan, the tumour area on CT increased by 3.1±57% in treated metastases compared with 23.3±32% in untreated metastases. A wide range of post-treatment changes of target lesions was observed on CT, including an increase in the size of hypodense lesions, necrotic features and complete resolution of CT abnormalities.Conclusion The metabolic information obtained from FDG-PET/CT seems to provide a more accurate and earlier assessment of therapy response following ⁹⁰Y microsphere treatment than does the anatomical CT information.     

A Computed Tomography-Based Spatial Normalization for the Analysis of [18F] Fluorodeoxyglucose Positron Emission Tomography of the Brain

Objective

We developed a new computed tomography (CT)-based spatial normalization method and CT template to demonstrate its usefulness in spatial normalization of positron emission tomography (PET) images with [¹⁸F] fluorodeoxyglucose (FDG) PET studies in healthy controls.

Materials and Methods

Seventy healthy controls underwent brain CT scan (120 KeV, 180 mAs, and 3 mm of thickness) and [¹⁸F] FDG PET scans using a PET/CT scanner. T1-weighted magnetic resonance (MR) images were acquired for all subjects. By averaging skull-stripped and spatially-normalized MR and CT images, we created skull-stripped MR and CT templates for spatial normalization. The skull-stripped MR and CT images were spatially normalized to each structural template. PET images were spatially normalized by applying spatial transformation parameters to normalize skull-stripped MR and CT images. A conventional perfusion PET template was used for PET-based spatial normalization. Regional standardized uptake values (SUV) measured by overlaying the template volume of interest (VOI) were compared to those measured with FreeSurfer-generated VOI (FSVOI).

Results

All three spatial normalization methods underestimated regional SUV values by 0.3-20% compared to those measured with FSVOI. The CT-based method showed slightly greater underestimation bias. Regional SUV values derived from all three spatial normalization methods were correlated significantly (p < 0.0001) with those measured with FSVOI.

Conclusion

CT-based spatial normalization may be an alternative method for structure-based spatial normalization of [¹⁸F] FDG PET when MR imaging is unavailable. Therefore, it is useful for PET/CT studies with various radiotracers whose uptake is expected to be limited to specific brain regions or highly variable within study population.     

Use of 3′-deoxy-3′-[18F]fluorothymidine PET to monitor early responses to radiation therapy in murine SCCVII tumors

Purpose 3′-Deoxy-3′-[¹⁸F]fluorothymidine (FLT) is a promising new radiopharmaceutical for imaging cell proliferation. We evaluated whether FLT PET can be used to monitor early responses to radiation treatment. Methods C3H/HeN mice bearing murine squamous cell carcinomas were randomized to irradiation with 0, 10, or 20 Gy. Twenty-four hours later, the mice were sacrificed for histopathological and biological assessment such as cell cycle analysis, Hoechst staining, and clonogenic cell survival assay. PET scans were performed on other mice after injection of [¹⁸F]FLT or [¹⁸F]fluorodeoxyglucose (FDG) before and after radiation treatment, and tumor growth was assessed over 9 days. Results Histopathological examination detected no morphological changes 24 h after radiation treatment, but cell cycle analysis showed that irradiated tumors had a decreased fraction of cells in S phase and an increased fraction in G2–M phase, compared with nonirradiated tumors. Irradiated tumors also had a higher incidence of apoptotic features and reduced clonogenic cell survival. Tumor growth was significantly delayed in irradiated mice (p<0.001) compared with control mice. PET images showed increased tumoral uptake of both FLT and FDG before radiation treatment. Following irradiation, FLT uptake differed significantly (p=0.020) from that in control mice. In contrast, FDG uptake after irradiation did not differ significantly from that in control mice. Conclusion Our finding that tumor uptake of FLT was reduced at 24 h after radiation treatment suggests that FLT PET may be a promising imaging modality for monitoring the early effects of radiation therapy.     

Peripheral nerve schwannoma: two cases exhibiting increased FDG uptake in early and delayed PET imaging

We present two cases of peripheral nerve schwannoma which showed an increased accumulation of 2-deoxy-[¹⁸F] fluoro-D-glucose (FDG) in the tumors on positron emission tomography (PET) imaging acquired at both 1 h (early phase) and 2 h (delayed phase) after FDG injection. FDG-PET scans were performed with a dedicated PET scanner (HeadtomeV/ SET2400 W, Shimadzu, Kyoto, Japan) and the PET data analyzed the most metabolically active region of interest (ROI). We set the maximum standardized uptake value (SUV max) with a cut-off point of 3.0 to distinguish benign and malignant lesions. Although the mechanism responsible for the increased FDG uptake in benign schwannomas remains unknown, we discuss our findings in the context of tumor cellularity and briefly review other studies on the subject.