18F-FDG PET/CT in evaluating non-CNS pediatric malignancies.

We reviewed our experience of (18)F-FDG PET/CT in noncentral nervous system (CNS) pediatric malignancies and evaluated if PET/CT provided additional information to conventional imaging (CI) examinations to determine the efficacy of this new imaging modality in the clinical setting. METHODS: One-hundred fifty-one consecutive FDG PET/CT examinations in 55 pediatric patients with non-CNS malignant tumors were reviewed. Among them, 108 PET/CT examinations were accompanied by CI, such as contrast CT or MRI, performed within a month of PET/CT in our hospital. Two radiologists reviewed the indication, purpose, and PET/CT findings and compared the findings with those of CI, if available, on the representative lesion in each of the 6 separate body regions. Positive findings included abnormal findings related to malignant lesions (suspected) as well as equivocal findings, in which the presence of malignancy could not be denied, but excluded findings considered to relate to past treatment. Accuracy of the findings was determined on the basis of the reference standard comprising histopathologic findings or informative follow-up of >1 y. An examination-based analysis was also performed in terms of additional information of PET/CT to CI. RESULTS: There were 56 PET/CT-positive-CI-positive, 26 PET/CT-positive-CI-negative, and 54 PET/CT-negative-CI-positive lesions in 108 PET/CT examinations accompanied by CI, of which 54, 20, and 52 exhibited accurate PET/CT findings, respectively. Seventeen of the 20 PET/CT true-positive-CI false-negative lesions represented small lymph nodes diagnosed as negative on CI. All 52 PET/CT true-negative-CI false-positive findings were observed in lesions in a posttreatment status including 30 mediastinal masses in lymphoma. Examination-based analysis revealed that additional information of PET/CT to CI was found in 37 (34%) of the 108 examinations: 23 (21%) as negative and 14 (13%) as positive PET/CT findings. CONCLUSION: PET/CT exhibited better diagnostic performance than CI and showed accurate findings in 90% (72/80) of lesions with discordant findings between them. Additional information of PET/CT to CI was observed in more than one third of examinations compared. PET/CT was demonstrated to be an accurate imaging modality in evaluating pediatric patients with non-CNS malignancies.     

Present and future of PET and PET/CT in gynaecologic malignancies

Objectives

To review the published data in literature on patients affected by gynaecological malignancies to establish the role of ¹⁸F-FDG positron emission tomography (PET) and PET/CT in comparison to conventional imaging (CI).

Materials and methods

All papers specifically addressed to the role of ¹⁸F-FDG PET and PET/CT in gynaecological malignancies published on PubMed/Medline, in abstracts from the principal international congresses, in the guidelines from national Societies that had appeared in literature until November 2009 were considered for the purpose of the present study.

Results and conclusions

The use of ¹⁸F-FDG PET, and even more of ¹⁸F-FDG PET/CT, is increasing in the follow up of patients with gynaecologic malignancies and suspected recurrent disease: there is evidence in the literature that ¹⁸F-FDG PET/CT has a higher sensitivity than CI in depicting occult metastatic spread. An interesting issue is represented by patients with ovarian cancer with an increase of the specific biomarker, CA-125, and negative/inconclusive findings at CI. The use of ¹⁸F-FDG PET in differential diagnosis and staging is more controversial, but there is some evidence that a baseline PET examination performed before commencing therapy, for staging purpose, is also useful to evaluate the response to chemoradiation treatment. In several papers it has been suggested a relevant role of ¹⁸F-FDG PET/CT in evaluating the entity of response to treatment and therefore to plan the subsequent therapeutic strategy.     

PET/CT for the staging and follow-up of patients with malignancies

Positron emission tomography (PET) and computed tomography (CT) complement each other's strengths in integrated PET/CT. PET is a highly sensitive modality to depict the whole-body distribution of positron-emitting biomarkers indicating tumour metabolic activity. However, conventional PET imaging is lacking detailed anatomical information to precisely localise pathologic findings. CT imaging can readily provide the required morphological data. Thus, integrated PET/CT represents an efficient tool for whole-body staging and functional assessment within one examination. Due to developments in system technology PET/CT devices are continually gaining spatial resolution and imaging speed. Whole-body imaging from the head to the upper thighs is accomplished in less than 20 min. Spatial resolution approaches 2–4 mm. Most PET/CT studies in oncology are performed with ¹⁸F-labelled fluoro-deoxy-d-glucose (FDG). FDG is a glucose analogue that is taken up and trapped within viable cells. An increased glycolytic activity is a characteristic in many types of cancers resulting in avid accumulation of FDG. These tumours excel as “hot spots” in FDG-PET/CT imaging. FDG-PET/CT proved to be of high diagnostic value in staging and restaging of different malignant diseases, such as colorectal cancer, lung cancer, breast cancer, head and neck cancer, malignant lymphomas, and many more. The standard whole-body coverage simplifies staging and speeds up decision processes to determine appropriate therapeutic strategies. Further development and implementation of new PET-tracers in clinical routine will continually increase the number of PET/CT indications. This promotes PET/CT as the imaging modality of choice for working-up of the most common tumour entities as well as some of the rare malignancies.     

Detection of recurrent rectal cancer with CT, MRI and PET/CT

Computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET) all have the potential to directly visualize local and distant relapse of colorectal cancer (CRC). Nevertheless, the role of diagnostic imaging for routine follow-up of CRC patients remains controversial. Although MRI and PET have advantages over CT in the detection of local recurrence, until now only a few surveillance programs recommend the use of annual CT for routine follow-up. The objective of this review is to elucidate the current status of diagnostic imaging for the detection of recurrent rectal cancer based on the recent literature and our own experience. Furthermore, an insight into contemporary surveillance programs and an outlook concerning a novel technical approach to moving-table MRI at 1.5 Tesla for staging purposes are given.     

The additional value of PET/CT over PET in FDG imaging of oesophageal cancer

Purpose The aim of this study was to assess the value of combined PET/CT compared with PET reviewed side-by-side with CT, in patients with oesophageal cancer, before and after surgery.Methods Forty-one FDG PET/CT studies were performed in 32 patients with oesophageal cancer, before surgery (n=18) or during follow-up after resection of the primary tumour (n=23). One hundred and fifteen sites suspicious for malignancy were evaluated. PET/CT was prospectively compared with PET reviewed side-by-side with CT, for detection, accurate localisation and characterisation of malignant sites. PET/CT performance in different anatomical regions was compared before and after surgery. The impact of fused data on patient management was retrospectively assessed.Results PET/CT had an incremental value over PET for interpretation of 25 of 115 sites (22%), changing the initial characterisation of ten sites to either malignant (n=1) or benign (n=9), and defining the precise anatomical location of 15 sites. PET/CT provided better specificity and accuracy than PET for detecting sites of oesophageal cancer (81% and 90% vs 59% and 83% respectively, p<0.01). Fusion was of special value for interpretation of cervical and abdomino-pelvic sites, for disease assessment in loco-regional lymph nodes before surgery and in regions of postoperative anatomical distortion. PET/CT had an impact on the further management of four patients (10%), by detecting nodal metastases that warranted disease upstaging (n=2) and by excluding disease in sites of benign uptake after surgery (n=2).Conclusion PET/CT improves the accuracy of FDG imaging in oesophageal cancer and provides data of diagnostic and therapeutic significance for further patient management.     

Imaging of female pelvic malignancies regarding MRI, CT, and PET/CT

Purpose

To compose diagnostic standard operating procedures for both clinical and imaging assessment for vulvar and vaginal cancer, for vaginal sarcoma, and for ovarian cancer.

Methods

The literature was reviewed for diagnosing the above mentioned malignancies in the female pelvis. Special focus herein lies in tumor representation in MRI, followed by the evaluation of CT and PET/CT for this topic.

Conclusion

MRI is a useful additional diagnostic complement but by no means replaces established methods of gynecologic diagnostics and ultrasound. In fact, MRI is only implemented in the guidelines for vulvar cancer. According to the current literature, CT is still the cross-sectional imaging modality of choice for evaluating ovarian cancer. PET/CT appears to have advantages for staging and follow-up in sarcomas and cancers of the ovaries.     

Attenuation correction of PET images with respiration-averaged CT images in PET/CT.

Attenuation correction (AC) of PET images with helical CT (HCT) in PET/CT matches only the spatial resolution of CT and PET, not the temporal resolution. We therefore proposed the use of respiration-averaged CT (ACT) to match the temporal resolution of CT and PET and evaluated the improvement of tumor quantification in PET images of the thorax with ACT. METHODS: First, we examined 100 consecutive clinical PET/CT studies for the frequency and magnitude of misalignment at the diaphragm position between the HCT and the PET data. Patients were injected with 555-740 MBq of (18)F-FDG and scanned 1 h after injection. The HCT data were acquired at the following settings: 120 kV, 300 mA, pitch of 1.35:1, collimation of 8 x 1.25 mm, and rotation cycle of 0.5 s. Patients were instructed to hold their breath at midexpiration during HCT of the thorax. The PET acquisition was 3 min per bed. Second, we retrospectively analyzed studies of 8 patients (1 with esophageal cancer and 7 with lung cancer). Each study included regular PET/CT followed by 4-dimensional (4D) CT for radiation treatment planning. We compared the results of AC of the PET data with HCT and ACT. There were 13 tumors in these 8 patients. The 4D CT data were acquired at the following settings: 120 kV, 50-150 mA, cine duration of 1 breathing cycle plus 1 s, collimation of 8 x 1.25 mm, and rotation cycle of 0.5 s. The acquisition was taken when the patient was in the free-breathing state. We averaged the 10 phases of the 4D CT data to obtain ACT for AC of the PET data. Both the ACT and the HCT data were used for AC of the same PET data. RESULTS: There was a misalignment between the HCT and the PET data in 50 of 100 patient studies. In 34 studies, the misalignment was greater than 2 cm. In a comparison of HCT and ACT, 5 tumors had differences in standardized uptake values (SUV) between HCT-and ACT-attenuation-corrected PET of less than 20%, and 4 tumors had differences in SUV of more than 50%. The latter 4 tumors were found in the patient with esophageal cancer and in 2 of the patients with lung cancer. The PET data from these 3 patients had a misalignment of 2-4.5 cm relative to the HCT data. Breathing artifacts were significantly reduced by ACT. Seven of the 8 patients had a lower diaphragm position on HCT than on ACT, suggesting that the patients tended to hold a deeper breath during HCT than during ACT. CONCLUSION: The high rate of misalignment suggested a potential mismatch between the HCT and the PET data with the limited-breath-hold CT protocol. In the comparison of HCT and ACT, significant differences (>50%) in SUV were attributable to different breathing states between HCT and PET. The PET data corrected by ACT did not show breathing artifacts, suggesting that ACT may be more accurate than HCT for AC of the PET data.     

Role of 18F-FDG PET/CT in management of high-grade salivary gland malignancies.

The role of 18F-FDG PET/CT for planning the treatment of high-grade salivary gland malignancies was investigated and was compared with that with using contrast-enhanced CT. METHODS: The subjects chosen for the study had high-grade cancer of the salivary gland, as confirmed by surgical pathology. The diagnostic values from 37 CT and PET/CT scans of 33 subjects were compared. The ability to predict the extent of the disease was compared by performing a subsite-based analysis for the primary lesions and a level-by-level analysis for the neck node levels as well as for the final TNM staging. The surgical pathology (67.6%) and clinical follow-up examinations (32.4%) were used as the reference standards. Furthermore, the changes made in each subject's care, based on a PET/CT examination, were compared with the treatment received without using the PET/CT data. RESULTS: Using a primary subsite-based analysis, the diagnostic accuracy for predicting the pathologic tumor extent was significantly higher for PET/CT (91.0%) compared with that using CT alone (70.1%, P < 0.001). For the neck nodes on a level-by-level analysis, the metastasis could be predicted more accurately on the basis of a PET/CT examination (97.6%) than with using only CT (86.0%, P = 0.01). PET/CT was also far superior to CT in terms of the TNM staging (83.7% vs. 62.1%, P = 0.03). For 43.2% of the subjects, changes in the clinical decision making were made as a result of the PET/CT scan data over what was previously determined by using the CT scans alone. CONCLUSION: PET/CT provides more accurate diagnostic information for the evaluation of high-grade salivary cancer than does CT and it has a major impact on making treatment decisions for patients with a high-grade salivary malignancy.     

CT and MR imaging of primary cardiac malignancies.

Primary cardiac malignancies are rare tumors that are difficult to diagnose clinically. Different primary cardiac malignancies may have different clinical, morphologic, and radiologic features and intracardiac locations. Angiosarcoma is the most common primary cardiac malignancy. It tends to occur in the right atrium and involve the pericardium. Because of its tendency to hemorrhage, angiosarcoma often demonstrates areas of increased signal intensity with T1-weighted sequences. Undifferentiated sarcomas typically occur in the left atrium and have variable epidemiologic and radiologic features. Rhabdomyosarcoma is the most common primary cardiac malignancy in children and is more likely than other primary cardiac sarcomas to involve the valves. Primary cardiac osteogenic sarcoma almost always occurs in the left atrium and frequently demonstrates calcification. Certain features (eg, broad base of attachment, origin at a site other than the atrial septum) help differentiate this tumor from left atrial myxoma. Leiomyosarcoma favors the left atrium and tends to invade the pulmonary veins and mitral valve. Fibrosarcoma also tends to occur in the left atrium and is often necrotic. Liposarcoma is very rare and usually manifests as a large, infiltrating mass. Foci of macroscopic fat are occasionally seen. Primary cardiac lymphoma occurs more commonly in immunocompromised patients, frequently involves the pericardium, and, unlike other primary cardiac malignancies, may respond to chemotherapy. The advent of cross-sectional imaging has allowed earlier detection of primary cardiac malignancies as well as more accurate diagnosis and characterization.     

FDG PET/CT in carcinoma of unknown primary

Carcinoma of unknown primary (CUP) is a heterogeneous group of metastatic malignancies in which a primary tumor could not be detected despite thorough diagnostic evaluation. Because of its high sensitivity for the detection of lesions, combined ¹⁸F-fluoro-2-deoxyglucose positron emission tomography (FDG PET)/computed tomography (CT) may be an excellent alternative to CT alone and conventional magnetic resonance imaging in detecting the unknown primary tumor. This article will review the use, diagnostic performance, and utility of FDG PET/CT in CUP and will discuss challenges and future considerations in the diagnostic management of CUP.     

PET/CT in lymphoma: prospective study of enhanced full-dose PET/CT versus unenhanced low-dose PET/CT.

PET/CT combines functional and morphologic data and increases diagnostic accuracy in a variety of malignancies. This study prospectively compares the agreement between contrast-enhanced full-dose PET/CT and unenhanced low-dose PET/CT in lesion detection and initial staging of Hodgkin's disease and non-Hodgkin's lymphoma. METHODS: Forty-seven biopsy-proven lymphoma patients underwent a 18F-FDG PET/CT study that included unenhanced low-dose CT and enhanced full-dose CT for initial staging. Patients who had undergone previous diagnostic CT for initial staging were excluded. For every patient, each modality of PET/CT images was evaluated by either of 2 pairs of readers, with each pair comprising 1 experienced radiologist and 1 experienced nuclear physician. While evaluating one of the 2 types of PET/CT, the readers were unaware of the results of the other type. Lesion detection, number of sites affected in each anatomic region, and disease stage were assessed. Agreement between techniques was determined by the kappa-statistic, and discordances were studied by the McNemar test. Clinical, analytic, histopathologic, diagnostic CT, and PET data; data from other imaging techniques; and follow-up data constituted the reference standard. RESULTS: For region-based analysis, no significant differences were found between unenhanced low-dose PET/CT and contrast-enhanced full-dose PET/CT, although full-dose PET/CT showed fewer indeterminate findings and a higher number of extranodal sites affected than did low-dose PET/CT. Agreement between the 2 types of PET/CT was almost perfect for disease stage (kappa = 0.92; P < 0.001). CONCLUSION: Our study showed a good correlation between unenhanced low-dose PET/CT and contrast-enhanced full-dose PET/CT for lymph node and extranodal disease in lymphomas, suggesting that unenhanced low-dose PET/CT might suffice in most patients as the only imaging technique for the initial staging of lymphomas, reserving diagnostic CT for selected cases.     

Limitations of CT during PET/CT.

Our aim was to determine the diagnostic limitations of low-dose, unenhanced CT scans performed for anatomic reference and attenuation correction during PET/CT. METHODS: The Radiology Information System at our oncologic hospital was queried during the 9-mo period from July 2002 to April 2003 for patients with PET/CT scans and diagnostic enhanced CT within 2 wk of each other. One radiologist interpreted the CT portion of the PET/CT (CT(p)) unaware of the PET results and the associated enhanced diagnostic CT (CT(d)). A medical student compared this interpretation with the official report of the CT(d) and listed all discrepancies between reports. A separate radiologist compared CT(p) and CT(d) images and classified true discrepant findings as due to lack of intravenous contrast, arm-position artifact, lack of enteric contrast, low milliamperage (mA), and quality of lung images. RESULTS: Among 100 patients, the most common malignancies were lymphoma (n = 37), cancer of the colorectum (n = 31), and esophageal cancer (n = 15). Among 194 true discrepancies in which findings were missed at CT(p), causes were as follows: (a) lack of intravenous contrast (128/194, 66%), (b) arm-down artifact (17/194, 9%), (c) quality of lung images (26/194, 13%), (d) lack of enteric contrast (15/194, 8%), and (e) low mA (8/194, 4%). Discrepancies were seen most commonly in detecting lymphadenopathy and visceral metastases. CONCLUSION: Most missed findings on the unenhanced CT portion of the PET/CT scans were due to technical factors that could be altered. Discrepant findings would have led to altered management in only 2 patients, suggesting a role for limited repeat imaging to reduce radiation and use of valuable resources.     

Metastases to the breast from extramammary malignancies – PET/CT findings

Detection of incidental malignant lesions in the breast has a significant clinical impact not only on healthy individuals but also on patients with known malignant disease. This review describes a spectrum of metastatic breast lesions incidentally detected by FDG PET-CT at staging that may be misinterpreted as second primary malignancy. The common non-mammary malignancies that metastasize to the breast include melanoma, hematopoietic malignancies and epithelial cancers. We present the FDG PET-CT features of incidental non-mammary metastases to the breast that may help distinguish primary breast cancer from metastatic disease and aid in the management of patients with a known malignancy.     

Detection of relevant colonic neoplasms with PET/CT: promising accuracy with minimal CT dose and a standardised PET cut-off

Objective:

To determine the performance of FDG-PET/CT in the detection of relevant colorectal neoplasms (adenomas ≥10 mm, with high-grade dysplasia, cancer) in relation to CT dose and contrast administration and to find a PET cut-off.

Methods:

84 patients, who underwent PET/CT and colonoscopy (n?=?79)/sigmoidoscopy (n?=?5) for ${\left( {{\hbox{79}} \times {\hbox{6}} + {\hbox{5}} \times {\hbox{2}}} \right)} = {\hbox{484}}$ colonic segments, were included in a retrospective study. The accuracy of low-dose PET/CT in detecting mass-positive segments was evaluated by ROC analysis by two blinded independent reviewers relative to contrast-enhanced PET/CT. On a per-lesion basis characteristic PET values were tested as cut-offs.

Results:

Low-dose PET/CT and contrast-enhanced PET/CT provide similar accuracies (area under the curve for the average ROC ratings 0.925 vs. 0.929, respectively). PET demonstrated all carcinomas (n?=?23) and 83% (30/36) of relevant adenomas. In all carcinomas and adenomas with high-grade dysplasia (n?=?10) the SUV_max was ≥5. This cut-off resulted in a better per-segment sensitivity and negative predictive value (NPV) than the average PET/CT reviews (sensitivity: 89% vs. 82%; NPV: 99% vs. 98%). All other tested cut-offs were inferior to the SUV_max.

Conclusion:

FDG-PET/CT provides promising accuracy for colorectal mass detection. Low dose and lack of iodine contrast in the CT component do not impact the accuracy. The PET cut-off SUV_max?≥?5 improves the accuracy.     

Detection of unknown primary neuroendocrine tumours (CUP-NET) using 68Ga-DOTA-NOC receptor PET/CT

Purpose

This bi-centric study aimed to determine the role of receptor PET/CT using ⁶⁸Ga-DOTA-NOC in the detection of undiagnosed primary sites of neuroendocrine tumours (NETs) and to understand the molecular behaviour of the primarily undiagnosed tumours.

Methods

Overall 59 patients (33 men and 26 women, age: 65?±?9 years) with documented NET and unknown primary were enrolled. PET/CT was performed after injection of approximately 100 MBq (46–260 MBq) of ⁶⁸Ga-DOTA-NOC. The maximum standardised uptake values (SUV_max) were calculated and compared with SUV_max in known pancreatic NET (pNET) and ileum/jejunum/duodenum (SI-NET). The results of PET/CT were also correlated with CT alone.

Results

In 35 of 59 patients (59%), ⁶⁸Ga-DOTA-NOC PET/CT localised the site of the primary: ileum/jejunum (14), pancreas (16), rectum/colon (2), lungs (2) and paraganglioma (1). CT alone (on retrospective analyses) confirmed the findings in 12 of 59 patients (20%). The mean SUV_max of identified previously unknown pNET and SI-NET were 18.6?±?9.8 (range: 7.8–34.8) and 9.1?±?6.0 (range: 4.2–27.8), respectively. SUV_max in patients with previously known pNET and SI-NET were 26.1?±?14.5 (range: 8.7–42.4) and 11.3?±?3.7 (range: 5.6–17.9). The SUV_max of the unknown pNET and SI-NET were significantly lower (p?<?0.05) as compared to the ones with known primary tumour sites; 19% of the patients had high-grade and 81% low-grade NET. Based on ⁶⁸Ga-DOTA-NOC receptor PET/CT, 6 of 59 patients were operated and the primary was removed (4 pancreatic, 1 ileal and 1 rectal tumour) resulting in a management change in approximately 10% of the patients. In the remaining 29 patients, because of the far advanced stage of the disease (due to distant metastases), the primary tumours were not operated. Additional histopathological sampling was available from one patient with bronchial carcinoid (through bronchoscopy).

Conclusion

Our data indicate that ⁶⁸Ga-DOTA-NOC PET/CT is highly superior to ¹¹¹In-OctreoScan (39% detection rate for CUP according to the literature) and can play a major role in the management of patients with CUP-NET.     

Nonossifying fibroma can mimic residual lymphoma in FDG PET: additional value of combined PET/CT

A 12-year-old girl was diagnosed with Hodgkin's lymphoma and underwent conventional cross-sectional imaging for initial staging. Chemotherapy was given according to standard pediatric protocols. At the end of therapy, an F-18 FDG PET/CT examination was performed to evaluate the therapeutic response. The scan demonstrated focal uptake of FDG in the right distal femur and residual lymphoma was taken into consideration. However, findings in the coregistered CT scan were consistent with nonossfiying fibroma, a common benign skeletal lesion. Combined PET/CT imaging can be helpful to identify benign bone lesions mimicking metastatic or residual disease in F-18 FDG PET as illustrated by this case.