|
|
|||||||||
Clinical Investigations |
Division of Nuclear Medicine, Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania
| ABSTRACT |
|---|
|
|
|---|
Key Words: PET 18F-FDG lung nodules metabolism dual time point
| INTRODUCTION |
|---|
|
|
|---|
In general, standardized uptake values (SUVs) of >2.5 appear to be suggestive of malignancy (3,79). However, several reports and observations on the day-to-day clinical practice indicate that a significant degree of overlap exists between the uptake values of benign and malignant lesions (4,5,7,8). Whereas some malignant lesions such as bronchioalveolar carcinoma can exhibit low uptake values (9), certain inflammatory lesions, including granulomatous processes, fungal infections, or bacterial infections, can be noted with SUVs of >2.5 (5,10), thereby limiting specificity of this method.
The variation in body habitus, duration of uptake period, plasma glucose levels, and partial-volume effects are important factors that influence the SUV level and have not been considered in a standard manner in the reported literature (11). Changes in these parametersespecially, elevated plasma glucose levels, short uptake periods, and small lesion sizeswill lead to low SUVs in malignant lesions, which lead to assumed low sensitivity for this powerful methodology.
Recently, investigators from the University of Pennsylvania reported the initial results of dual time point imaging in animal models (12) and in patient studies (12,13). Hustinx et al. (13) performed dual time point scanning on 21 patients with 18 head and neck malignant tumors and 9 inflammatory or infectious lesions. The authors noted that tumors had an average SUV increase of 12% between the first and second scan, whereas inflammatory lesions and structures with physiologic uptake of 18F-FDG (tongue, larynx) showed essentially stable uptake over time or a slight decline. Another important finding was that the SUV changes in tumors were larger when >30 min had elapsed between the first and second emission scans.
The purpose of this study was to determine whether obtaining 2 sequential emission scans on patients with pulmonary nodules, to measure the uptake values (SUVs) in the lesions, can result in accuracy of the test in separating benign from malignant lesions.
| MATERIALS AND METHODS |
|---|
|
|
|---|
18F-FDG was synthesized using the method described by Hamacher et al. (14). Image acquisition for the whole-body scan started at a mean time point of 69 min (range, 55110 min) after injection of 2.52 MBq/kg of body weight. This first scan (scan 1) started on all patients at the shoulders and included thorax, abdomen, and pelvis. It consisted of 4 or 5 emission frames of 25.6-cm length with an overlap of 12.8 cm covering an axial length of 6476.8 cm. After an interval of 56 min (range, 4964 min), a second emission scan of the thorax only (scan 2) was acquired on all patients at a mean time of 122 min after tracer injection (range, 100163 min). Starting at the same position as scan 1, it covered an axial length of 25.638.4 cm (1 or 2 frames). A transmission scan was obtained with both sets of images for attenuation correction. Image reconstruction was performed with an iterative ordered-subsets expectation maximization algorithm with 4 iterations and 8 subsets (15). Attenuation-corrected images were obtained by applying transmission maps, which were acquired after 18F-FDG injection with a 137Cs source interleaved with the emissions scans (16,17).
Regions of interest (ROIs) were overlaid onto the fully corrected PET images of scans 1 and 2 in the area of the known radiographic lung density. This was achieved by direct visual assessment of the lesion position on the CT scan and subsequent identification of the corresponding area on PET scans 1 and 2.
The margins of these ROIs were placed at approximately 50% of the maximal counts of the highest lesion counting density. The ROI was then transferred to the other scan of the same patient. In tumor lesions that extended over several slices in the craniocaudal direction, the ROI was placed in the midportion of the lesion where the maximal counts were measured. If no discernible uptake was present on either PET scan, ROIs were drawn in the presumed location that corresponded best with that of the radiographic density. Because the patients did not have to leave the scanning table between the end of the first and the beginning of the second emission scan, only minimal correction was required in a few cases because of patient motion.
The SUV was calculated according to the following standard formula (3):
![]() |
The presence of malignancy was proven by obtaining a biopsy or by resecting the lesion in 19 patients. In 1 patient with clinical and radiographic findings highly suggestive of a malignancy, no tissue diagnosis was established. In addition, this patient responded favorably to radiation therapy, which further enhanced the presumed diagnosis. The lack of a malignant process was established in 2 of 18 patients by resecting the lesion. In the remaining 16 patients, stability (or resolution in 1 patient) of the lesion on radiographic examination over an extended period of time (1826 mo) was considered as evidence for a benign process.
| RESULTS |
|---|
|
|
|---|
|
|
2.5. Figure 1 shows a 1.8 x 1.0 cm lesion in the right lower lobe (lesion 9). The SUV was 1.45 on scan 1 and 1.72 on scan 2. The uptake increased by 18.6% between the scans. Biopsy of this lesion revealed a moderately differentiated adenocarcinoma. Figure 2 shows the images of lesion 29. This patient had a 0.8-cm density in the left upper lobe. SUV measurements were 1.54 (scan 1) and 1.50 (scan 2), a minor decrease of 2.6%. The thoracic surgeon elected to resect the nodule, which revealed a benign granuloma.
|
|
The SUV increase methods yielded a most accurate result when an SUV threshold of 10% was used. By adopting an SUV increase of >10% between the first and second scans as a criterion for malignancy, all 20 neoplastic lesions were identified correctly and 16 of 18 lesions were diagnosed correctly as being benign. When an SUV increase of >5% was used as the threshold, the sensitivity, specificity, and accuracy were 100%, 61%, and 82%, respectively. When a threshold of 15% was used, the sensitivity, specificity, and accuracy were 60%, 94%, and 76%, respectively. Therefore, the sensitivity for this method was 100% while the specificity and accuracy remained quite high, equaling 89% and 95%, respectively, when a threshold of 10% was used to diagnose a malignant lung nodule.
| DISCUSSION |
|---|
|
|
|---|
However, other investigators have found that determination of the SUV suffers from significant limitations. Hamberg et al. (18) showed that the usual scan start times of 4560 min lead to significant underestimation of the true SUV because, in most tumors, 18F-FDG uptake continues to rise beyond this period and typically does not reach a plateau for several hours. In untreated tumors, 95% of the plateau value was reached at 298 ± 42 min, with a range of 130500 min. Although the authors found a positive correlation between the glucose metabolic rate and the SUV, the value was only R2 = 0.65, indicating a considerable margin of error.
Lodge et al. (19) came to a similar conclusion in a study of 29 patients with various benign and malignant soft-tissue masses. High-grade sarcomas reached the maximal 18F-FDG uptake at 4 h, whereas uptake in benign lesions reached its maximal value within 30 min. In this study, the diagnostic value of Patlak or nonlinear regression analysis was not superior to SUV measurements at 4 h. The authors believed that 1 possible explanation might be the poor counting statistics and increased noise several hours after 18F-FDG injection.
These results are in contrast to a study by Lowe et al. (20), who assessed the change in SUV over time in a cohort of 14 patients with pulmonary abnormalities (10 malignant, 4 benign). On the basis of measurement of the signal-to-noise ratio, the best separation between benign and malignant lesions occurred at 50 min after injection and no improvement was seen at later time points.
In view of the encouraging results by Hustinx et al. (13), who acquired scans at 2 time points for head and neck tumors, we adopted this study approach for the evaluation of pulmonary nodules. The percentage SUV change between the first and second scans with a threshold of 10% increase in measured values provided a higher sensitivity (100% vs. 80%), while maintaining an excellent specificity (89% vs. 94%), than that obtained from a single image acquisition using the usual SUV threshold method.
The results of this study for the sensitivity and specificity measures by adopting the SUV threshold of 2.5 are similar to those published in the literature (18). However, there was a clear benefit of calculating the percentage SUV change between the 2 scans compared with the SUV threshold alone. Four neoplastic lesions of 1.5- to 2.0-cm maximal diameter showed relatively low uptake values on scans 1 and 2 but showed a considerable increase in the SUV between these 2 scans. None of these lesions was of a histologic type that is known to frequently exhibit low-uptake values, such as bronchioalveolar carcinoma. The SUV measurements of these 4 relatively small lesions could be underestimated because of volume averaging (10). There was a marked percentage increase in SUV in these 4 lesions (mean, 19.5%), which was not significantly different from that of the entire group of malignant lesions. One explanation for this phenomenon is that, at the time of the second emission scan (approximately 2 h), the peak 18F-FDG concentration is not reached in most malignant lesions. On the basis of the results of Hamberg et al. (18) and Lodge et al. (19), the likely mechanism appears to be that most neoplasms continue to accumulate 18F-FDG for several hours after injection.
The results of this study and those of other reports (18,19) provide an argument for adopting an extended scanning protocol, which involves imaging the pulmonary nodules at 2 time points. In particular, small- and medium-sized lesions, which may not be detected because of the limited resolution of the technique or relatively low glucose utilization (secondary to a low rate of cell division), could be identified as malignant on the basis of an increased SUV over time.
Although there was no difference between the standard SUV threshold and the percentage SUV change method for identifying benign lesions in this study, the latter method may prove advantageous when uptake values are close to the threshold of 2.5. Acquiring a second scan that reveals stable or declining uptake values suggests a benign lesion and reduces the need for surgical exploration in such indeterminate cases.
Two lesions (lesions 28 and 35) with a high likelihood of benign etiology showed increases of >10% of their SUVs (12.7% and 29.3%) over time. The patient with significant increase continues to show no evidence of malignant features in her lung lesion. Because of the patients general medical condition and the stability of the lesion, no biopsy has been obtained so far to clarify the etiology of the lesion. Given the generally very low uptake values of either of these 2 lesions, we conclude that the application of the threshold technique probably has no value in lesions with SUV of <1.0.
The limitation of our study is the small number of patients. This study did not include any bronchioalveolar carcinoma, which sometimes does not show any increased 18F-FDG activity. This study included only 18 benign lung nodules with 2 false-positive results. Some benign granulomatous lesions, such as sarcoidosis, aspergillosis, and coccidiomycosis, have been reported to be 18F-FDG avid and to show increasing uptake over time (20,21), resulting in false-positive studies. Thus, patients with granulomatous disease or bronchioalveolar carcinoma are the main causes of false-positive and false-negative studies.
Finally, if one should make a final interpretation of the study solely on the basis of the change in the SUV, rigorous attention to technique is paramount for the evaluation of pulmonary nodules. A change of 10% between the early and late images is very small when the SUV is small, and any patients motion between the 2 scans can significantly affect and falsify the result. The change in the SUV is also dependent of the reproducibility of the ROI between both scans.
On the basis of the data reported in this article, the dual time point scan protocol is relatively simple and is practical in the setting of a clinical PET center.
| CONCLUSION |
|---|
|
|
|---|
| ACKNOWLEDGMENTS |
|---|
| FOOTNOTES |
|---|
For correspondence or reprints contact: Abass Alavi, MD, Division of Nuclear Medicine, Hospital of the University of Pennsylvania, 110 Donner Building, 3400 Spruce St., Philadelphia, PA 19104.
E-mail: alavi{at}oasis.rad.upenn.edu
| REFERENCES |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
M. Imbriaco, M. G. Caprio, G. Limite, L. Pace, T. De Falco, E. Capuano, and M. Salvatore Dual-Time-Point 18F-FDG PET/CT Versus Dynamic Breast MRI of Suspicious Breast Lesions Am. J. Roentgenol., November 1, 2008; 191(5): 1323 - 1330. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. J. Hicks Time and Again, Children Resemble Their Parents J. Nucl. Med., October 1, 2008; 49(10): 1577 - 1578. [Full Text] [PDF] |
||||
![]() |
D. Uesaka, Y. Demura, T. Ishizaki, S. Ameshima, I. Miyamori, M. Sasaki, Y. Fujibayashi, and H. Okazawa Evaluation of Dual-Time-Point 18F-FDG PET for Staging in Patients with Lung Cancer J. Nucl. Med., October 1, 2008; 49(10): 1606 - 1612. [Abstract] [Full Text] [PDF] |
||||
![]() |
C.-J. Chen, B.-F. Lee, W.-J. Yao, L. Cheng, P.-S. Wu, C. L. Chu, and N.-T. Chiu Dual-Phase 18F-FDG PET in the Diagnosis of Pulmonary Nodules with an Initial Standard Uptake Value Less Than 2.5 Am. J. Roentgenol., August 1, 2008; 191(2): 475 - 479. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. M. Wahidi, J. A. Govert, R. K. Goudar, M. K. Gould, and D. C. McCrory Evidence for the Treatment of Patients With Pulmonary Nodules: When Is It Lung Cancer?: ACCP Evidence-Based Clinical Practice Guidelines (2nd Edition) Chest, September 1, 2007; 132(3_suppl): 94S - 107S. [Abstract] [Full Text] [PDF] |
||||
![]() |
D. A. Torigian, S. S. Huang, M. Houseni, and A. Alavi Functional Imaging of Cancer with Emphasis on Molecular Techniques CA Cancer J Clin, July 1, 2007; 57(4): 206 - 224. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. M. Blodgett, C. C. Meltzer, and D. W. Townsend PET/CT: Form and Function Radiology, February 1, 2007; 242(2): 360 - 385. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. Mavi, M. Urhan, J. Q. Yu, H. Zhuang, M. Houseni, T. F. Cermik, D. Thiruvenkatasamy, B. Czerniecki, M. Schnall, and A. Alavi Dual Time Point 18F-FDG PET Imaging Detects Breast Cancer with High Sensitivity and Correlates Well with Histologic Subtypes J. Nucl. Med., September 1, 2006; 47(9): 1440 - 1446. [Abstract] [Full Text] [PDF] |
||||
![]() |
N. Avril 18F-FDG PET After Radiofrequency Ablation: Is Timing Everything? J. Nucl. Med., August 1, 2006; 47(8): 1235 - 1237. [Full Text] [PDF] |
||||
![]() |
Y. Nishiyama, Y. Yamamoto, K. Fukunaga, N. Kimura, A. Miki, Y. Sasakawa, H. Wakabayashi, K. Satoh, and M. Ohkawa Dual-Time-Point 18F-FDG PET for the Evaluation of Gallbladder Carcinoma J. Nucl. Med., April 1, 2006; 47(4): 633 - 638. [Abstract] [Full Text] [PDF] |
||||
![]() |
T. Bunyaviroch and R. E. Coleman PET Evaluation of Lung Cancer J. Nucl. Med., March 1, 2006; 47(3): 451 - 469. [Full Text] [PDF] |
||||
![]() |
R. Kumar, V. A. Loving, A. Chauhan, H. Zhuang, S. Mitchell, and A. Alavi Potential of Dual-Time-Point Imaging to Improve Breast Cancer Diagnosis with 18F-FDG PET J. Nucl. Med., November 1, 2005; 46(11): 1819 - 1824. [Abstract] [Full Text] [PDF] |
||||
![]() |
U. Nestle, S. Kremp, A. Schaefer-Schuler, C. Sebastian-Welsch, D. Hellwig, C. Rube, and C.-M. Kirsch Comparison of Different Methods for Delineation of 18F-FDG PET-Positive Tissue for Target Volume Definition in Radiotherapy of Patients with Non-Small Cell Lung Cancer J. Nucl. Med., August 1, 2005; 46(8): 1342 - 1348. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. J. Reinhardt, H. Strunk, T. Gerhardt, R. Roedel, U. Jaeger, J. Bucerius, T. Sauerbruch, H.-J. Biersack, and F. L. Dumoulin Detection of Klatskin's Tumor in Extrahepatic Bile Duct Strictures Using Delayed 18F-FDG PET/CT: Preliminary Results for 22 Patient Studies J. Nucl. Med., July 1, 2005; 46(7): 1158 - 1163. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. M. Spence, M. Muzi, D. A. Mankoff, S. F. O'Sullivan, J. M. Link, T. K. Lewellen, B. Lewellen, P. Pham, S. Minoshima, K. Swanson, et al. 18F-FDG PET of Gliomas at Delayed Intervals: Improved Distinction Between Tumor and Normal Gray Matter J. Nucl. Med., October 1, 2004; 45(10): 1653 - 1659. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. L. Aquino and A. J. Fischman Does Whole-Body 2-[18F]-Fluoro-2-Deoxy-D-Glucose Positron Emission Tomography Have an Advantage Over Thoracic Positron Emission Tomography for Staging Patients With Lung Cancer? Chest, September 1, 2004; 126(3): 755 - 760. [Abstract] [Full Text] [PDF] |
||||
![]() |
E. M. Rohren, T. G. Turkington, and R. E. Coleman Clinical Applications of PET in Oncology Radiology, May 1, 2004; 231(2): 305 - 332. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. G. Strauss, A. Dimitrakopoulou-Strauss, and U. Haberkorn Shortened PET Data Acquisition Protocol for the Quantification of 18F-FDG Kinetics J. Nucl. Med., December 1, 2003; 44(12): 1933 - 1939. [Abstract] [Full Text] [PDF] |
||||
![]() |
V H Gerbaudo, S Britz-Cunningham, D J Sugarbaker, and S T Treves Metabolic significance of the pattern, intensity and kinetics of 18F-FDG uptake in malignant pleural mesothelioma Thorax, December 1, 2003; 58(12): 1077 - 1082. [Abstract] [Full Text] [PDF] |
||||
![]() |
S.-Y. Ma, L.-C. See, C.-H. Lai, H.-H. Chou, C.-S. Tsai, K.-K. Ng, S. Hsueh, W.-J. Lin, J.-T. Chen, and T.-C. Yen Delayed 18F-FDG PET for Detection of Paraaortic Lymph Node Metastases in Cervical Cancer Patients J. Nucl. Med., November 1, 2003; 44(11): 1775 - 1783. [Abstract] [Full Text] [PDF] |
||||
![]() |
T.-C. Yen, K.-K. Ng, S.-Y. Ma, H.-H. Chou, C.-S. Tsai, S. Hsueh, T.-C. Chang, J.-H. Hong, L.-C. See, W.-J. Lin, et al. Value of Dual-Phase 2-Fluoro-2-Deoxy-D-Glucose Positron Emission Tomography in Cervical Cancer J. Clin. Oncol., October 1, 2003; 21(19): 3651 - 3658. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. Beaulieu, P. Kinahan, J. Tseng, L. K. Dunnwald, E. K. Schubert, P. Pham, B. Lewellen, and D. A. Mankoff SUV Varies with Time After Injection in 18F-FDG PET of Breast Cancer: Characterization and Method to Adjust for Time Differences J. Nucl. Med., July 1, 2003; 44(7): 1044 - 1050. [Abstract] [Full Text] [PDF] |
||||
![]() |
Y. Demura, T. Tsuchida, T. Ishizaki, S. Mizuno, Y. Totani, S. Ameshima, I. Miyamori, M. Sasaki, and Y. Yonekura 18F-FDG Accumulation with PET for Differentiation Between Benign and Malignant Lesions in the Thorax J. Nucl. Med., April 1, 2003; 44(4): 540 - 548. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | RSS | TABLE OF CONTENTS |
| JOURNAL OF NUCLEAR MEDICINE TECHNOLOGY | THE JOURNAL OF NUCLEAR MEDICINE |