Regional 2-[18F]fluoro-2-deoxy-d-glucose uptake varies in normal lung

2-[¹⁸F]fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) is a promising imaging procedure for detecting primary and metastatic cancer in the lungs. We have, however, failed to detect some small tumors in the lower lobes of the lungs. This study aimed to determine whether increase¹⁸F background activity in the dependent lower lungs is present, which could make lesion detection more difficult. We measured the standardized uptake values (SUVs) for FDG of normal lung remote from the nodular lesion in 16 patients with newly diagnosed untreated lung lesions stronlgy suspected to represent non-small cell lung cancers. In addition, 15 patients with known or suspected primary breast cancers without pulmonary lesions were included as control subjects. After PET transmission images of the thorax were obtained, approximately 370 MBq of FDG was injected intravenously and imaging was immediately begun. Patients were supine throughout the study. SUVs were determined with images obtained 50–70 min after FDG injection. Regions of interest (ROls) of 6×6 pixels were positioned over normal lung in anterior, mid, and posterior portions of upper, middle, and lower lung fields. Thus, as many as 18 ROls were positioned in each patient. The SUVs of the posterior portion were significantly higher than those of the anterior and mid portions in the population of 31 cases (P <0.001). Also, the mean SUV of the lower lung field was significantly higher than the SUVs of the upper and middle lung fields in this population (P <0.01). This pattern was seen among the two groups of 16 patients suspected of having lung cancer and 15 control subjects. Background¹⁸F activity was highest in posterior and lower lung in these patients. The maximum value of mean SUV observed in normal posterior lower lung was 0.804±0.230 (41% greater than the mean SUV in the anterior upper lung), which is in the range of the apparent SUV for a 5-mm lung lesion, with higher SUV, due to recovery coefficient issues. Thus this phenomenon could contribute to occasional false-negative lesions in those areas. Increased blood flow and FDG delivery and also scatter from heart and liver may contribute to the increased lower lung background activity. Regional differences in normal lung FDG uptake are significant and should be considered when interpreting pulmonary PET studies in patients with suspected primary or metastatic lung cancer.     

Effect of respiratory gating on quantifying PET images of lung cancer.

We have developed a new technique to gate lung 18F-FDG PET images in synchronization with the respiratory motion to reduce smearing due to breathing and improve quantitation of 18F-FDG uptake in lung lesions. METHODS: A camera-based respiratory gating system, the real-time position management (RPM), is used to monitor the respiratory cycle. The RPM provides a trigger to the PET scanner to initiate the gating cycle. Each respiratory cycle is divided into discrete bins triggered at a defined amplitude or phase within the patient's breathing motion, into which PET data are acquired. The acquired data within the time bins correspond to different lesion positions within the breathing cycle. The study includes 5 patients with lung cancer. RESULTS: Measurements of the lesions' volumes in the gated mode showed a reduction of up to 34% compared with that of the nongated measurement. This reduction in the lesion volume has been accompanied by an increase in the intensity in the 18F-FDG signal per voxel. This finding has resulted in an improvement in measurement of the maximum standardized uptake value (SUV(max)), which increased in 1 patient by as much as 159%. The total lesion glycolysis, defined as the product of the SUV(max) and the lesion volume, was also measured in gated and nongated modes and showed a consistency between the 2 measurements. CONCLUSION: We have shown that image smearing can be reduced by gating 18F-FDG PET images in synchronization with the respiratory motion. This technique allows a more accurate definition of the lesion volume and improves the quantitation specific activity of the tracer (in this case, 18F-FDG), which are distorted because of the breathing motion.     

呼吸门控PET/CT对肺部结节SUV的影响

目的 观察呼吸门控与非门控PET/CT显像测定肺部结节SUV的差异,探讨不同呼吸时相SUV变化趋势.方法 2010年5月至2011年3月进行PET/CT显像、发现有多个肺部结节并同意进行呼吸门控显像者共19例,最终14例共37个结节纳入该研究,其中男6例,女8例,年龄29 ～ 80(63.7±7.1)岁.对所有患者进行常规和呼吸门控PET/CT采集.经过后台处理得到呼吸时相相匹配的1个呼吸周期内6个时相的PET/CT融合图像.测得SUV,每个肺部结节的每个指标均进行非门控与门控显像6个时相共7次测量.采用SPSS 13.0软件对数据行t检验、秩和检验和相关分析.结果 37个肺部结节呼吸门控显像的SUVmax和SUVmean分别为13.69±6.70和8.56±4.11,明显高于非门控PET/CT的12.76±6.74及7.66±4.00(t =3.475和Z=-3.661,P均＜0.001);但2种显像技术SUVmax与SUVmean相关性好(r=0.971和0.969,P均＜0.05);在门控显像中,6个时相不同时相间SUV以时相1即吸气末最高,而时相4(呼气末吸气初)最低.37个结节中4个结节常规显像SUV＜ 2.5(定义为轻度摄取),其中有1个结节SUVmax由非门控显像的2.13升至门控显像的2.52.结论 采用呼吸门控PET/CT显像所得到的肺部结节SUVmax和SUVmean比非门控常规采集高,但两者相关性好;SUV不同时相间以吸气末最高.对轻度摄取FDG的结节,经呼吸门控PET/CT其SUV有所提高,有可能影响临床诊断.     

符合线路显像与PET显像中SUV的比较研究

目的比较符合线路显像标准摄取值(SUV)与PET显像的SUV。方法用双探头符合显像仪及PET对模型显像，分别采用不同的重建算法重建，测定图像上热灶的SUV。结果对直径小于30mm热灶，相同大小时，PET、得到的SUV高于符合线路显像；无论对PET还是符合线路显像，随热灶大小增加SUV增加；SUV与重建算法有关；选取的感兴趣区(ROI)越大，获得的SUV越小；由PET图像获得的热灶SUV可见，当热灶大于2倍的系统分辨率时，SUCmax接近热灶的真实值(SUVmax)。结论符合线路显像的SUV低于PET显像；病灶大小、重建算法、ROI大小均影响SUV。     

Respiratory motion artefact in the liver dome on FDG PET/CT: comparison of attenuation correction with CT and a caesium external source

Purpose Respiratory motion has been reported to be a potential cause of artefacts on PET/CT, and of errors in the quantification of lesion activity due to inaccurate attenuation correction. We examined FDG images corrected for attenuation with CT and a caesium external source in the same patients to study this artefact and to assess its impact on detection of lesions in the upper part of the liver.Methods A total of 122 patients underwent the examination using both attenuation correction techniques, with the Gemini PET/CT scanner. No breathing instructions were given. The images obtained were visually compared, and standardised uptake values (SUVs) in 35 lesions were measured (mean SUV/normal liver SUV) in 14 patients with lesions in the upper part of the liver (less than 5 cm from the upper border).Results CT-corrected images of the liver included an artefactual cold area in 84 patients (69%); this area was located in the posterior upper part of the liver (65 patients, 53%), included the top of the liver (ten patients, 8%) or affected both the top and the posterior part (nine patients, 8%). In lesions (and also in normal liver outside the artefactual area), SUVs obtained with CT correction were higher than those obtained with Cs correction (p<0.05), though this was usually without relevance for lesion detection. However, in patients with lesions situated inside the artefactual area, SUVs were lower with CT correction, and ability to detect two lesions (6%) was affected.Conclusion Failure to detect a liver lesion (especially in the superior and posterior parts) is a rare but possible pitfall when using only CT-corrected FDG images.     

Effect of corrections for blood glucose and body size on [18F]FDG PET standardised uptake values in lung cancer

Standardised uptake values (SUVs) are commonly used as a semi-quantitative index of 2-[18F]fluoro-2-deoxy-D-glucose (FDG) tracer uptake in positron emission tomography (PET). Studies have shown that SUVs may depend on body size and blood glucose concentration and corrections for these effects have been proposed in the literature. This retrospective study investigated the effect of the proposed corrections on SUVs from a group of 154 patients with lung cancer who had scans on a dedicated PET scanner. A total of 252 SUVs were requested as an aid to staging during consideration for surgical resection. SUVs were calculated normalised to body weight (SUVw), lean body mass (SUV(LBM)) and body surface area (SUV(BSA)). The following correlations were examined: SUV with height, weight and body surface area for the different body size normalisations; SUVw and SUVw x blood glucose (SUV(BG)) with blood glucose; SUVw with scan time post injection; and SUVw with apparent lesion diameter. Significant correlations were only observed between: SUV(LBM) and height (P=0.007); SUVw and scan time (P=0.007); SUVw and lesion diameter (P=0.0005); and SUV(BG) and blood glucose (P<0.00001). The correlation between SUV(LBM) and height suggests that lean body mass as a function of height alone should not be used to normalise SUVs; however, the lean body mass calculated from a height and weight nomogram did not show this effect. The strong correlation between SUV(BG) and blood glucose concentration suggests that for non-diabetic fasted patients, lung tumour SUVs should not be adjusted for blood glucose.     

Deep-inspiration breath-hold PET/CT of the thorax.

The goal of this study was to describe our initial experience with the deep-inspiration breath-hold (DIBH) technique in combined PET/CT of the thorax. This article presents particular emphasis on the technical aspects required for clinical implementation. METHODS: In the DIBH technique, the patient is verbally coached and brought to a reproducible deep inspiration breath-hold level. The first "Hold" period, which refers to the CT session, is considered as the reference. This is followed by 9- to 20-s independent breath-hold PET acquisitions. The goal is to correct for respiratory motion artifacts and, consequently, improve the tumor quantitation and localization on the PET/CT images and inflate the lungs for possible improvement in the detection of subcentimeter pulmonary nodules. A physicist monitors and records patient breathing during PET/CT acquisition using a motion tracker. Patient breathing traces obtained during acquisition are examined on the fly to assess the reproducibility of the technique. RESULTS: Data from 8 patients, encompassing 10 lesions, were analyzed. Visual inspection of fused PET/CT images showed improved spatial matching between the 2 modalities, reduced motion artifacts especially in the diaphragm, and increased the measured standardized uptake value (SUV) attributed to reduced motion blurring, as compared with the standard clinical PET/CT images. CONCLUSION: The practice of DIBH PET/CT is feasible in a clinical setting. With this technique, consistent lung inflation levels are achieved during PET/CT sessions, as judged by both motion tracker and verification of spatial matching between PET and CT images. Breathing-induced motion artifacts are significantly reduced using DIBH compared with free breathing, enabling better target localization and quantitation. The DIBH technique showed an increase in the median SUV by 32.46%, with a range from 4% to 83%, compared with SUVs measured on the clinical images. The median percentage reduction in the PET-to-CT lesions' centroids was 26.6% (range, 3%-50%).     

28. Accuracy of Qualitative and Semiquantitative Analysis of 18FDG Positron Emission Tomography Scans in the Evaluation of Primary and Metastatic Lesions

Background: 18FDG PET scans are often interpreted on the basis of visual estimation of regional tracer uptake. Whether semiquantitative analysis may help clinicians in the recognition of neoplastic masses still remains debated.Materials and Methods: 134 patients with 144 dubious lesions on CT scans (89 pulmonary, 16 hepatic, 39 soft tissue) were studied by means of PET and 18(F)fluorodeoxyglucose. PET images were qualitatively interpreted by the consensus of two nuclear physicians. Standardized uptake value (SUV) and SUV lean were quantified in both normal and suspicious tissues. SUVs results in the lesion were also expressed as normalized values for the normal mean value in each organ (SUVs/org) and for the overall mean value in normal tissues (SUVs/norm).Results: All patients underwent cytological and/or hystological evaluation of the lesions: 53/144 (37%) were recognized as negative while 91/144 (63%) as positive for primary or metastatic disease. Qualitative analysis resulted in 75% specificity and 93% sensitivity. SUVs, SUVs lean, SUVs/org and SUVs/norm resulted significantly (p < 0.001) higher in positive than in negative lesions by cytology/histology. ROC curves analysis provided optimal cut-off values of 2.5, 0.8, 2.5 and 3, for SUVs, SUVs lean, SUVs/org and SUVs/norm, respectively. Using these cut-offs, specificity and sensitivity resulted 90 and 94%, 83 and 97%, 88 and 93%, 94 and 93%, respectively.Conclusion: Our data suggest that, in patients with CT scan suspicious lesions, visual analysis of PET scans is affected by a high number of false negative results. Semiquantitative assessment of regional metabolic activity has an incremental value and should be used in PET scan interpretation of dubious lesions.     

Cause and magnitude of the error induced by oral CT contrast agent in CT-based attenuation correction of PET emission studies.

CT images represent essentially noiseless maps of photon attenuation at a range of 40-140 keV. Current dual-modality PET/CT scanners transform them into attenuation coefficients at 511 keV and use these for PET attenuation correction. The proportional scaling algorithms hereby used account for the different properties of soft tissue and bone but are not prepared to handle material with other attenuation characteristics, such as oral CT contrast agents. As a consequence, CT-based attenuation correction in the presence of an oral contrast agent results in erroneous PET standardized uptake values (SUVs). The present study assessed these errors with phantom measurements and patient data. METHODS: Two oral CT contrast agents were imaged at 3 different concentrations in dual-modality CT and PET transmission studies to investigate their attenuation properties. The SUV error due to the presence of contrast agent in CT-based attenuation correction was estimated in 10 patients with gastrointestinal tumors as follows. The PET data were attenuation corrected on the basis of the original contrast-enhanced CT images, resulting in PET images with distorted SUVs. A second reconstruction used modified CT images wherein the CT numbers representing contrast agent had been replaced by CT values producing approximately the right PET attenuation coefficients. These CT values had been derived from the data of 10 patients imaged without a CT contrast agent. The SUV error, defined as the difference between both sets of SUV images, was evaluated in regions with oral CT contrast agent, in tumor, and in reference tissue. RESULTS: The oral CT contrast agents studied increased the attenuation for 511-keV photons minimally, even at the highest concentrations found in the patients. For a CT value of 500 Hounsfield units, the proportional scaling algorithm therefore overestimated the PET attenuation coefficient by 26.2%. The resulting SUV error in the patient studies was highest in regions containing CT contrast agent (4.4% +/- 2.8%; maximum, 11.3%), whereas 1.2% +/- 1.1% (maximum, 4.1%) was found in tumors, and 0.6% +/- 0.7% was found in the reference. CONCLUSION: The use of oral contrast agents in CT has only a small effect on the SUV, and this small effect does not appear to be medically significant.     

PET/CT: artifacts caused by bowel motion

BACKGROUND AND AIM: In a combined positron emission tomography (PET) and computed tomography (CT) system, the CT images can be used for attenuation correction as well as for image fusion. However, quantitative and qualitative differences have been reported between CT based attenuation corrected PET and conventional transmission scan corrected PET images. The purpose of this study was to investigate potential differences in PET/CT caused by attenuation differences in bowel due to motion. METHODS: Twelve patients had PET/CT scans performed using 68Ge transmission and CT attenuation correction methods. Three emission imaging datasets were generated including CT corrected PET, Ge corrected PET, and the difference images (CT corrected PET minus Ge corrected PET). PET difference images were used to identify regions of mismatch and to quantify possible discordance between images by using standardized uptake values (SUVs). Using the Ge corrected PET as the standard, differences in emission images were classified as an overestimation (pattern A) or an underestimation (pattern B) in these difference images. RESULTS: One hundred and twenty-three mismatched areas were identified. Among them, overestimated areas in CT corrected image were detected in 36 regions (pattern A), while underestimated areas were evaluated in the remaining 87 regions (pattern B). The mean value of the difference in pattern A (mean +/- standard deviation = 0.84 +/- 0.44) was slightly higher than that in pattern B (0.60 +/- 0.23), and statistically significant. Six of 36 regions in pattern A had an SUV of greater than 2.5 in CT corrected PET but less than 2.5 in Ge corrected PET; two of 87 regions with pattern B demonstrated an SUV greater than 2.5 in Ge corrected PET and less than 2.5 in CT corrected PET. CONCLUSION: Physiological bowel motion may result in attenuation differences and subsequent differences in SUVs. Overestimation of fluorodeoxyglucose uptake should not be misinterpreted as disease.     

Cystic Fibrosis: Detecting Changes in Airway Inflammation with FDG PET/CT

Purpose: To determine if fluorine 18 fluorodeoxyglucose (FDG) positron emission tomographic (PET)/computed tomographic (CT) imaging can depict a treatment effect from intravenous antibiotics for pulmonary exacerbation in cystic fibrosis (CF). Materials and Methods: The study was approved by the institutional review board of the Hospital for Sick Children and by Health Canada. Consent was obtained from all subjects. Patients with CF who were between 6 and 18 years of age and were admitted for a pulmonary exacerbation were eligible for the study. FDG PET/CT examinations (with low-dose CT) were performed on days 1 and 14 of admission (±72 hours). PET activity was quantified by using standardized uptake values (SUVs) through assessment of background activity (mean SUV [SUV(mean)]) and superimposed focal uptake (maximum SUV [SUV(max)]) for each lung zone. CT studies were scored by using the CF-CT model. SUVs from pre- and posttherapy studies were compared by using paired t tests. Unpaired t tests were used to compare data in patients with CF and data in 10 control subjects. Results: Twenty patients with CF were enrolled. Antibiotic therapy resulted in a significant decrease in SUV(max) (mean difference, 2.3 ± 2.1 [standard deviation], P < .0001). Pretherapy SUV(max) and SUV(mean) and posttherapy SUV(max) were significantly different from those in control subjects. The change in SUV(max) and percentage predicted forced expiratory volume in 1 second was negatively correlated. (R = -0.72, P = .004). Overall CF-CT scores significantly correlated with SUV(max) (R = 0.40, P = .01). Conclusion: FDG PET/CT is a useful tool for detecting inflammatory changes resulting from treatment for pulmonary exacerbations in pediatric patients with CF. Inflammatory changes detected by using FDG PET/CT correlated with lung function, sputum neutrophil counts, and CF-CT scores. Analyzing focal lung inflammation (with SUV(max)) may be a feasible way to measure airway inflammation in patients with CF. ? RSNA, 2012 Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12111873/-/DC1.     

Need for standardization of 18F-FDG PET/CT for treatment response assessments

Many factors affect standardized uptake values (SUVs) in (18)F-FDG PET/CT. The use of the SUV from a single PET scan in multicenter studies requires the standardization of (18)F-FDG PET/CT procedures. In the context of treatment response assessments (repeated PET scans), many factors may seem to have minor effects on percentage changes in SUVs, provided that imaging procedures are executed in a consistent manner for each subject. However, the use of (18)F-FDG PET/CT in a nonstandardized manner will result in unknown biases and reproducibilities of SUVs and SUV-based response measures. This article provides an overview of the need for standardization in relation to the specific use of SUVs and SUV changes in studies of treatment response assessments.     

Mediastinal staging of lung cancer with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose positron emission tomography and a dual-head coincidence gamma camera

The aims of the present study were (a) to evaluate mediastinal staging in patients with lung cancer with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) using a coincidence gamma camera (hybrid PET) in comparison with dedicated positron emission tomography (PET) and computed tomography (CT), and (b) to assess the feasibility to determine standardized uptake values (SUV) with hybrid PET. Forty patients were included in the study. Hybrid PET was performed without and with attenuation correction. Data were rebinned with single-slice (SSRB) or Fourier rebinning (FORE). The SUVs of primary tumors were calculated with hybrid PET and compared with SUVs determined by dedicated PET. Diagnostic accuracy for hybrid with or without attenuation correction was 80 or 74% compared with 82% for dedicated PET, and 63% for CT. Attenuation-corrected hybrid PET revealed a higher specificity than CT (83 vs 52%; p<0.05). The SUVs of primary tumors were similar to those of hybrid PET and dedicated PET with a mean relative difference of 20.8±16.4%. The FORE improved the agreement of SUVs with a mean relative difference of 13.8±9.9 vs 36.0±17.9% for SSRB (p<0.001). Hybrid PET with attenuation correction is more specific than CT for mediastinal staging in patients with lung cancer (p<0.05). It reveals similar results in comparison with dedicated PET. Calculation of SUVs with hybrid PET is feasible. Electronic Publication     

Deep-inspiration breath-hold PET/CT: clinical findings with a new technique for detection and characterization of thoracic lesions.

Respiratory motion during PET/CT acquisition can cause misregistration and inaccuracies in calculation of standardized uptake values (SUVs). Our aim was to compare the detection and characterization of thoracic lesions on PET/CT with and without a deep-inspiration protocol. METHODS: We studied 15 patients with suspected pulmonary lesions who underwent clinical PET/CT, followed by deep-inspiration breath-hold (BH) PET/CT. In BH CT, the whole chest of the patient was scanned in 15 s at the end of deep inspiration. For BH PET, patients were asked to hold their breath 9 times for 20-s intervals. One radiologist reviewed images, aiming to detect and characterize pulmonary, nodal, and skeletal abnormalities. Clinical CT and BH CT were compared for number, size, and location of lesions. Lesion SUVs were compared between clinical PET and BH PET. Images were also visually assessed for accuracy of fusion and registration. RESULTS: All patients had lesions on clinical CT and BH CT. Pulmonary BH CT detected more lesions than clinical CT in 13 of 15 patients (86.7%). The total number of lung lesions detected increased from 53 with clinical CT to 82 with BH CT (P<0.001). Eleven patients showed a total of 31 lesions with abnormal (18)F-FDG uptake. BH PET/CT had the advantage of reducing misregistration and permitted a better localization of sites with (18)F-FDG uptake. A higher SUV was noted in 22 of 31 lesions on BH PET compared with clinical PET, with an average increase in SUV of 14%. CONCLUSION: BH PET/CT enabled an increased detection and better characterization of thoracic lesions compared with a standard PET/CT protocol, in addition to more precise localization and quantification of the findings. The technique is easy to implement in clinical practice and requires only a minor increase in the examination time.     

Fluorodeoxyglucose positron emission tomography pattern of pulmonary lymphangitic carcinomatosis

OBJECTIVE: The purpose of this study was to evaluate the F-fluorodeoxyglucose (FDG) positron emission tomography (PET) uptake in pulmonary lymphangitic carcinomatosis identified on computed tomography (CT) in patients with lung cancer. METHODS: This was a retrospective analysis of F-FDG PET images in 7 patients (4 male and 3 female, mean age: 56.6 +/- 6.6 years) with lung cancer with a CT-based diagnosis of lymphangitic carcinomatosis. The F-FDG PET scans in a group of 7 patients (4 male and 3 female, mean age: 42.1 +/- 5.66 years) with normal chest CT scans served as a control group. Mean standardized uptake values (SUVs) were calculated based on average tumor uptake, initial injected activity, and body weight. RESULTS: The intensity of F-FDG uptake in diseased lung is significantly greater than in corresponding normal contralateral lung or in the lungs of normal controls (P = 0.003). The ratio of the SUV of lung with lymphangitic carcinomatosis to corresponding contralateral normal lung was significantly increased (P = 0.006), and the ratio of the SUV of mediastinal blood pool to lung with lymphangitic carcinomatosis was significantly decreased (P = 0.0002). CONCLUSION: There is diffuse increased FDG uptake in the lung corresponding to the CT pattern of lymphangitic carcinomatosis.     

Three-region MRI-based whole-body attenuation correction for automated PET reconstruction

IntroductionIn this study we proposed and developed a simple attenuation mapping approach based on magnetic resonance imaging (MRI) for the purpose of reconstructing positron emission tomography (PET) images in PET/MRI imaging devices.MethodsAfter experimental development, an in vivo calibration was performed by whole-body scanning of five beagles on both a PET/CT and an MRI. The attenuation was determined by using an automated segmentation algorithm to segment regions of background, lung, soft tissue and bone, and assigning them values of 0.002, 0.030, 0.098 and 0.130 cm^?1, respectively.ResultsThe CT-attenuated and MRI-attenuated PET images had average standardized uptake values (SUVs) that differed by 1–6% for most regions of interest (ROIs). Also, mean relative differences (MRDs) between the images were between 5% and 9% for most regions. The only exception is bone, where the three-region MRI-attenuated PET images had an SUV 10% less on average than the CT-attenuation images, and the MRD averaged 14%. Also, additional segmentation of the bone in the four-region MRI-attenuated PET images reduced the SUV difference to 3% and the MRD to 6%.ConclusionTherefore, despite the improvements in the four-region segmentation, the three-region segmentation, without delineation of osseous tissues, produces high-quality images that are sufficient for most expected clinical and research purposes.     

Correction for oral contrast artifacts in CT attenuation-corrected PET images obtained by combined PET/CT.

Recent studies have shown increased artifacts in CT attenuation-corrected (CTAC) PET images acquired with oral contrast agents because of misclassification of contrast as bone. We have developed an algorithm, segmented contrast correction (SCC), to properly transform CT numbers in the contrast regions from CT energies (40-140 keV) to PET energy at 511 keV. METHODS: A bilinear transformation, equivalent to that supplied by the PET/CT scanner manufacturer, for the conversion of linear attenuation coefficients of normal tissues from CT to PET energies was optimized for BaSO(4) contrast agent. This transformation was validated by comparison with the linear attenuation coefficients measured for BaSO(4) at concentrations ranging from 0% to 80% at 511 keV for PET transmission images acquired with (68)Ge rod sources. In the CT images, the contrast regions were contoured to exclude bony structures and then segmented on the basis of a minimum threshold CT number (300 Hounsfield units). The CT number in each pixel identified with contrast was transformed into the corresponding effective bone CT number to produce the correct attenuation coefficient when the data were translated by the manufacturer software into PET energy during the process of CT attenuation correction. CT images were then used for attenuation correction of PET emission data. The algorithm was validated with a phantom in which a lesion was simulated within a volume of BaSO(4) contrast and in the presence of a human vertebral bony structure. Regions of interest in the lesion, bone, and contrast on emission PET images reconstructed with and without the SCC algorithm were analyzed. The results were compared with those for images obtained with (68)Ge-based transmission attenuation-corrected PET. RESULTS: The SCC algorithm was able to correct for contrast artifacts in CTAC PET images. In the phantom studies, the use of SCC resulted in an approximate 32% reduction in the apparent activity concentration in the lesion compared with data obtained from PET images without SCC and a <7.6% reduction compared with data obtained from (68)Ge-based attenuation-corrected PET images. In one clinical study, maximum standardized uptake value (SUV(max)) measurements for the lesion, bladder, and bowel were, respectively, 14.52, 13.63, and 13.34 g/mL in CTAC PET images, 59.45, 26.71, and 37.22 g/mL in (68)Ge-based attenuation-corrected PET images, and 11.05, 6.66, and 6.33 g/mL in CTAC PET images with SCC. CONCLUSION: Correction of oral contrast artifacts in PET images obtained by combined PET/CT yielded more accurate quantitation of the lesion and other, normal structures. The algorithm was tested in a clinical case, in which SUV(max) measurements showed discrepancies of 2%, 1.3%, and 5% between (68)Ge-based attenuation-corrected PET images and CTAC PET images with SCC for the lesion, bladder, and bowel, respectively. These values correspond to 6.5%, 62%, and 66% differences between CTAC-based measurements and (68)Ge-based ones.     

Evaluation of various corrections to the standardized uptake value for diagnosis of pulmonary malignancy

OBJECTIVE: Standard uptake values (SUVs) are widely used for quantifying the uptake of 18F-fluorodeoxyglucose (18F-FDG) in tumours. The objective of this study was to evaluate the accuracy of SUVs for malignancy in lung nodules/masses and to analyse the effects of tumour size, blood glucose levels and different body weight corrections on SUV. METHODS: One hundred and twenty-seven patients with suspicious lung lesions imaged with 18F-FDG positron emission tomography (PET) were studied retrospectively. Pathology results were used to establish lesion diagnosis in all cases. SUVs based on maximum pixel values were obtained by placing regions of interest around the focus of abnormal 18F-FDG uptake in the lungs. The SUVs were calculated using the following normalizations: body weight (BW), lean body weight (LBW), scaled body surface area (BSA), blood glucose level (Glu) and tumour size (Tsize). Receivers operating characteristic (ROC) curves were generated to compare the accuracy of different methods of SUV calculation. RESULTS: The areas under the ROC curves for SUV(BW), SUV(BW+Glu), SUV(LBW), SUV(LBW+Glu), SUV(BSA), SUV(BSA+Glu) and SUV(BW+Tsize) were 0.915, 0.912, 0.911, 0.912, 0.916, 0.909 and 0.864, respectively. CONCLUSION: The accuracy of SUV analysis for malignancy in lung nodules/masses is not improved by correction for blood glucose or tumour size or by normalizing for body surface area or lean body weight instead of body weight.     

CT-based attenuation correction in the calculation of semi-quantitative indices of [<Superscript>18</Superscript>F]FDG uptake in PET

The introduction of combined PET/CT systems has a number of advantages, including the utilisation of CT images for PET attenuation correction (AC). The potential advantage compared with existing methodology is less noisy transmission maps within shorter times of acquisition. The objective of our investigation was to assess the accuracy of CT attenuation correction (CTAC) and to study resulting bias and signal to noise ratio (SNR) in image-derived semi-quantitative uptake indices. A combined PET/CT system (GE Discovery LS) was used. Different size phantoms containing variable density components were used to assess the inherent accuracy of a bilinear transformation in the conversion of CT images to 511 keV attenuation maps. This was followed by a phantom study simulating tumour imaging conditions, with a tumour to background ratio of 5:1. An additional variable was the inclusion of contrast agent at different concentration levels. A CT scan was carried out followed by 5 min emission with 1-h and 3-min transmission frames. Clinical data were acquired in 50 patients, who had a CT scan under normal breathing conditions (CTAC(nb)) or under breath-hold with inspiration (CTAC(insp)) or expiration (CTAC(exp)), followed by a PET scan of 5 and 3 min per bed position for the emission and transmission scans respectively. Phantom and patient studies were reconstructed using segmented AC (SAC) and CTAC. In addition, measured AC (MAC) was performed for the phantom study using the 1-h transmission frame. Comparing the attenuation coefficients obtained using the CT- and the rod source-based attenuation maps, differences of 3% and <6% were recorded before and after segmentation of the measured transmission maps. Differences of up to 6% and 8% were found in the average count density (SUV(avg)) between the phantom images reconstructed with MAC and those reconstructed with CTAC and SAC respectively. In the case of CTAC, the difference increased up to 27% with the presence of contrast agent. The presence of metallic implants led to underestimation in the surrounding SUV(avg) and increasing non-uniformity in the proximity of the implant. The patient study revealed no statistically significant differences in the SUV(avg) between either CTAC(nb) or CTAC(exp) and SAC-reconstructed images. The larger differences were recorded in the lung. Both the phantom and the patient studies revealed an average increase of approximately 25% in the SNR for the CTAC-reconstructed emission images compared with the SAC-reconstructed images. In conclusion, CTAC(nb) or CTAC(exp) is a viable alternative to SAC for whole-body studies. With CTAC, careful consideration should be given to interpretation of images and use of SUVs in the presence of oral contrast and in the proximity of metallic implants.     

FDG PET in the evaluation of the aggressiveness of pulmonary adenocarcinoma: correlation with histopathological features

2-[Fluorine-18]fluoro-2-deoxy-d-glucose (FDG) uptake within the primary lesion correlates with survival on positron emission tomography (PET) studies of patients with non-small cell lung cancer. The more metabolically active the tumour, the worse the outcome. The aim of this study was to determine whether a correlation exists between aggressiveness as determined by pathology and the findings of FDG PET in pulmonary adenocarcinoma. Thirty-five patients with 38 adenocarcinomas of the lung were studied. All patients underwent thoracotomy within 4 weeks of the FDG PET study. For semiquantitative analysis, standardized uptake values (SUVs) were calculated. Patients were classified into high SUV (> or = 4.0) and low SUV (<4.0) groups. The degree of FDG uptake (SUVs) in primary lung lesions was correlated with the histopathological features of aggressiveness (pleural involvement, vascular invasion or lymphatic permeation). The mean SUV of aggressive adenocarcinomas (4.36+/-1.94, n = 22) was higher than that of non-aggressive ones (1.53+/-0.88, n = 16) (P < 0.0001). Tumours with a high FDG uptake have a significantly higher likelihood of aggressiveness than those with a low FDG uptake (P = 0.0004). Analysis by the Kaplan-Meier methods revealed that the groups had different prognoses (log-rank test, P = 0.0099). The high SUV group had a significantly worse prognosis. In conclusion, a correlation was seen between aggressiveness as determined by pathology and glucose metabolism as measured by FDG PET in adenocarcinoma of the lung. FDG PET may be used as a non-invasive diagnostic technique in measuring aggressiveness and prognosis in patients with pulmonary adenocarcinoma.