Radiology: Perfusion CT may best PET/CT in pulmonary nodule assessment

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Axial fused image (SUVmax, 2.2) of after RF ablation at FDG PET/CT.
Image source: Deandreis et al. Radiology 2011; 258:270-276.

Dynamic first-pass area-detector perfusion CT may provide improved specificity and accuracy in the differentiation of malignant from benign pulmonary nodules compared with PET/CT, according to a study published in the February issue of Radiology.

Pulmonary nodule diagnosis and management is characterized by a challenging conundrum: surgeons should promptly operate on patients with operable malignant nodules while sparing patients with benign lesions from unnecessary thoracotomy. “Therefore, it is essential that one be able to differentiate malignant from benign nodules in the least invasive manner and make the most specific and accurate diagnosis,” wrote Yoshiharu Ohno, MD, PhD, of the department of radiology at Kobe University Graduate School of Medicine in Japan.

Existing methods of pulmonary nodule differentiation—CT, MR, PET, PET/CT—are plagued by false-negative and/or false-positive results. Ohno and colleagues sought to determine if whole organ perfusion CT might provide a more accurate evaluation of pulmonary nodules than PET/CT.

The researchers enrolled a final cohort of 50 patients with 76 pulmonary nodules between January 2008 and May 2009 to undergo dynamic first-pass area-detector perfusion CT, FDG PET/CT, transbronchial or percutaneous biopsy, bronchoalveolar lavage, microbiologic exam, resection via thoracotomy and video-assisted thoracic surgery or follow-up CT. Nodules were classified as malignant, benign nodules with expected low biologic activity and benign nodules with expected high biologic activity.

A chest radiologist with 15 years experience determined pulmonary nodule regions of interest (ROIs) on CT images, and researchers quantitatively analyzed image datasets to obtain perfusion via the maximum slope model (PF MS), extraction fraction (EF PP) and blood volume (BV PP). They also obtained maximal standard uptake value (SUV max) on PET/CT images for comparison.

After analyzing and comparing the data, the researchers found significant and excellent correlations between each dynamic CT index and SUV max and positive correlation between PF MS and EF pp, BV PP and SUV max.

They also reported that mean values for all parameters significantly differed in the malignant nodule group and the benign nodule with low biologic activity group. PF MS and EF PP in the malignant group significantly differed from the benign group with expected high biologic activity. The results of receiver operating characteristic analyses for distinguishing the three nodules groups revealed that areas under the receiver operating characteristics curve were significantly larger for PF MS and EF PP than for BV PP and SUV max. PF MS and EF pp provided greater specificity and accuracy at 79 percent and 90 percent, respectively, for PF ms and 82 percent and 86 percent, respectively, for EF PP than BV pp and SUV.

“Our results show significant and reproducible difference in SUV max and in all of the evaluated dynamic first-pass area-detector CT indexes among the malignant nodules, benign nodules with expected low biologic activity and benign nodules with expected high biologic activity,” summed Ohno and colleagues. The CT method also “enabled more specific and accurate differentiation between the malignant and benign pulmonary nodule groups than did PET/CT,” leading the researchers to “suggest that perfusion CT indexes could replace SUV max for functional assessment of pulmonary nodules.”

Observing differences among specific CT indexes, the researchers noted that PF MS and EF pp outperformed BV pp andSUVmax in terms of specificity and accuracy of pulmonary nodule differentiation. Thus, blood flow parameters such as PF MS and EF pp may more precisely and accurately analyze an increase in tumor angiogenesis than BV pp. Moreover, PF MS provided more accurate positive and negative predictive values, which “could help physicians provide immediate treatment for patients with malignant nodules and help avoid surgery or further intervention for patients without malignant nodules,” offered the researchers.

Ohno and colleagues suggested that future studies include and examine with dynamic area-detector CT and PET/CT all pulmonary nodules (regardless of size) detected at initial screening to further evaluate the clinical utility of the model. Nevertheless, they summed that the CT indexes