Measurement of apparent diffusion coefficient with simultaneous MR/positron emission tomography in patients with peritoneal carcinomatosis: comparison with 18F-FDG-PET.

PURPOSE: To characterize peritoneal carcinomatosis (PC) of different histologically proven primary tumors based on diffusion-weighted imaging (DWI) and (18) F-FDG positron emission tomography (PET). MATERIALS AND METHODS: Forty-one patients underwent simultaneous MR/PET after clinically indicated (18) F-FDG-PET/CT. For all patients, histology of the primary tumor was obtained. MR protocol comprised anatomical imaging and axial DWI. Apparent diffusion coefficient (ADC) maps and FDG-PET were co-registered for evaluation of ADC and standard uptake value (SUV) of peritoneal lesions. Both lesion- and patient-based analysis was performed. Up to four peritoneal lesions were evaluated per patient. Mean and maximum standard uptake value (SUVmean , SUVmax ), mean and minimum ADC (ADCmean , ADCmin ) of each lesion were assessed. Spearman rank correlation (rs ) of ADC and SUV were calculated. SUV and ADC of ovarian and colorectal cancer lesions were compared using Wilcoxon test. RESULTS: Measurable lesions (n = 52) were found in 20 of 41 PC patients. Moderate, but significant correlation existed between ADC and SUV in the lesion-based as well as the patient-based analysis (lesion-based: SUVmean versus ADCmean rs = -0.58; SUVmax versus ADCmin rs = -0.56, all P < 0.0001; patient-based: SUVmean versus ADCmean rs = -0.64, P = 0.002; SUVmax versus ADCmin rs = -0.60, P = 0.005). ADC and SUV differed significantly between ovarian and colorectal cancer lesions (ADCmin : P < 0.0001; ADCmean : P < 0.0001; SUVmax : P = 0.002; SUVmean : P = 0.005). Overall, mucinous tumor entities showed a tendency to higher ADC and lower SUV. CONCLUSION: PC lesions showed significant differences in glucose uptake and diffusion characteristics depending on primary tumor histology. These differences should be considered when interpreting FDG-PET and DWI in PC patients.

Pulmonary lesion assessment: comparison of whole-body hybrid MR/PET and PET/CT imaging--pilot study.

PURPOSE: To compare the performance of magnetic resonance (MR)/positron emission tomography (PET) imaging in the staging of lung cancer with that of PET/computed tomography (CT) as the reference standard and to compare the quantification accuracy of a new whole-body MR/PET system with corresponding PET/CT data sets. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. Ten patients in whom bronchial carcinoma was proven or clinically suspected underwent clinically indicated fluorine 18 fluorodeoxyglucose (FDG) PET/CT and, immediately thereafter, whole-body MR/PET imaging with a new hybrid whole-body system (3.0-T MR imager with integrated PET system). Attenuation correction of MR/PET images was segmentation based with fat-water separation. Tumor-to-liver ratios were calculated and compared between PET/CT and MR/PET imaging. Tumor staging on the basis of the PET/CT and MR/PET studies was performed by two readers. Spearman rank correlation was used for comparison of data. RESULTS: MR/PET imaging provided diagnostic image quality in all patients, with good tumor delineation. Most lesions (nine of 10) showed pronounced FDG uptake. One lesion was morphologically suspicious for malignancy at CT and MR imaging but showed no FDG uptake. MR/PET imaging had higher mean tumor-to-liver ratios than did PET/CT (4.4 ± 2.0 [standard deviation] for PET/CT vs 8.0 ± 3.9 for MR/PET imaging). Significant correlation regarding the tumor-to-liver ratio was found between both imaging units (ρ = 0.93; P < .001). Identical TNM scores based on MR/PET and PET/CT data were found in seven of 10 patients. Differences in T and/or N staging occurred mainly owing to modality-inherent differences in lesion size measurement. CONCLUSION: MR/PET imaging of the lung is feasible and provides diagnostic image quality in the assessment of pulmonary masses. Similar lesion characterization and tumor stage were found in comparing PET/CT and MR/PET images in most patients.

Single and dual energy attenuation correction in PET/CT in the presence of iodine based contrast agents.

In present positron emission tomography (PET)/computed tomography (CT) scanners, PET attenuation correction is performed by relying on the information given by a single CT scan. The scaling of the linear attenuation coefficients from CT x-ray energy to PET 511 keV gamma energy is prone to errors especially in the presence of CT contrast agents. Attenuation correction based upon two CT scans at different energies but performed at the same time and patient position should reduce such errors and therefore improve the accuracy of the reconstructed PET images at the cost of introduced additional noise. Such CT scans could be provided by future PET/CT scanners that have either dual source CT or energy sensitive CT. Three different dual energy scaling methods for attenuation correction are introduced and assessed by measurements with a modified NEMA 1994 phantom with different CT contrast agent concentrations. The scaling is achieved by differentiating between (1) Compton and photoelectric effect, (2) atomic number and density, or (3) water-bone and water-iodine scaling schemes. The scaling method (3) is called hybrid dual energy computed tomography attenuation correction (hybrid DECTAC). All three dual energy scaling methods lead to a reduction of contrast agent artifacts with respect to single energy scaling. The hybrid DECTAC method resulted in PET images with the weakest artifacts. Both, the hybrid DECTAC and Compton/photoelectric effect scaling resulted also in images with the lowest PET background variability. Atomic number/density scaling and Compton/photoelectric effect scaling had problems to correctly scale water, hybrid DECTAC scaling and single energy scaling to correctly scale Teflon. Atomic number/density scaling and hybrid DECTAC could be generalized to reduce these problems.

Fixation devices for whole-body 18F-FDG PET/CT: patient perspectives and technical aspects.

OBJECTIVE: To evaluate the use of a fixation device in whole-body postiron emission tomography/computed tomography (PET/CT). METHODS: Two hundred and thirty patients were prospectively included over a period of 3 months. Different single-phase and multiphase contrast-enhanced PET/CT protocols were used for whole-body examination. An unforced expiration state was applied as breathing protocol for CT examination. Patients were placed on a deflating device (1.0 m x 1.5 m) with arms elevated but supported in order to prevent full extension in shoulders and elbows providing comfortable positioning. Image quality was assessed by means of alignment of the liver quantitatively on co-registered PET/CT images. After the examination, patients were asked to complete a survey on subjective sensations such as pain in different body regions (yes/no). They were asked to give a final evaluation for the whole-body PET/CT examination (comfortable/not comfortable). Additionally, a control group (n=30) was assessed without the aid of additional devices. RESULTS: Examination protocols using the device showed minor misalignment of 5 mm. Different protocols did not reveal significant differences in misalignment. When comparing the control group misalignment was significantly higher with approx. 7 mm. The majority (75%) evaluated the positioning as comfortable despite 46% of the patients in this group feeling more or less severe pain in at least one body region. For controls, misalignment was slightly higher whereas only 39% found the positioning comfortable (chi(2)=13.03; P<0.0005) and 61% reported pain (NS). CONCLUSION: Both the technical aspects and patient evaluations favour the use of the vacuum device in whole-body PET/CT examinations. In particular, in time consuming protocols using multiphase CT examination the fixation device leads to excellent co-registration quality and patient compliance.

Low dose non-enhanced CT versus standard dose contrast-enhanced CT in combined PET/CT protocols for staging and therapy planning in non-small cell lung cancer.

PURPOSE: To evaluate low dose non-enhanced CT and standard dose contrast-enhanced CT in combined PET/CT protocols for staging and therapy planning of non-small cell lung cancer (NSCLC). METHODS: Retrospective analysis was performed of 50 consecutive patients with proven NSCLC who had been referred for primary staging (n=41) or restaging (n=9). All patients underwent a multi-phase PET/CT consisting of a low dose non-enhanced attenuation scan and an arterial and portal-venous contrast-enhanced CT scan followed by whole-body PET. Fused datasets of non-enhanced and contrast-enhanced PET/CT were compared per patient by using the TNM staging system, and per lesion regarding localisation, characterisation and delineation of tumour lesions. The staging results were validated either by histopathology or by clinical-radiological follow-up for >or=6 months. RESULTS: In 47/50 patients, the results of T staging did not differ between the two PET/CT protocols. Three patients could only be correctly classified as having T4 tumours after contrast application. Regarding N staging, both protocols yielded the same results. In M staging, there was only one patient with an improvement of the results as a result of contrast application. The lesion-based analysis of 92 sites showed no difference in the accuracy of lesion localisation and only one revision of lesion characterisation by contrast-enhanced PET/CT. The assessment of tumour delineation was altered by contrast application in 58/92 sites (p<0.0001). In 10/50 patients, contrast-enhanced PET/CT detected additional clinically important findings. CONCLUSION: In patients with advanced NSCLC, contrast-enhanced CT as part of the PET/CT protocol more accurately assessed the TNM stage in 8% of patients compared with non-contrast PET/CT. However, for planning of 3D conformal radiotherapy and non-conventional surgery, contrast-enhanced PET/CT protocols are indispensable owing to their superiority in precisely defining the tumour extent.

Optimized contrast-enhanced CT protocols for diagnostic whole-body 18F-FDG PET/CT: technical aspects of single-phase versus multiphase CT imaging.

UNLABELLED: The purpose of this study was to compare various PET/CT examination protocols that use contrast-enhanced single-phase or contrast-enhanced multiphase CT scans under different breathing conditions. METHODS: Sixty patients with different malignant tumors were randomized into 4 different PET/CT protocols. Single-phase protocols included an intravenous contrast-enhanced (Ultravist 370; iodine at 370 mg/mL) single-phase whole-body CT scan (90 mL at 1.8 mL/min; delay, 90 s) during shallow breathing (protocol A) or during normal expiration (NormExp; protocol B). Multiphase protocols included 2 separate CT scans in the arterial contrast enhancement phase (90 mL at 2.5-2.8 mL/min; bolus tracking; scan range, base of the skull to the kidneys) and the portal-venous contrast enhancement phase (delay, 90 s; scan range, base of the lungs to the proximal thighs) during shallow breathing (protocol C) or during NormExp (protocol D) followed by a low-dose CT scan during shallow breathing for attenuation correction and whole-body PET. Feasibility was assessed by comparing the misalignment of the upper abdominal organs quantitatively by means of the craniocaudal, lateral, and anterior-posterior differences on coregistered PET/CT images. For image quality, the occurrence of CT artifacts and mismatching of rigid body points were evaluated qualitatively. RESULTS: Misalignment was significantly lower for protocol B in almost all organs and represented the best coregistration quality. Surprisingly, protocol A showed significantly better alignment than the multiphase CT scans during NormExp. Misalignment values between the multiphase protocols were not significantly different, with a trend toward lower values for protocol D. The best CT image quality, with a significantly lower occurrence of artifacts, was found for protocols B and D (NormExp). The levels of mismatching of rigid body points because of patient movement in between the transmission and emission scans were similar for all protocols. CONCLUSION: Multiphase CT protocols presented a technical disadvantage represented by suboptimal image coregistration compared with single-phase protocols. Nevertheless, multiphase protocols are technically feasible and should be considered for patients who will benefit from a contrast-enhanced multiphase CT examination for diagnosis.

The benefit of functional-anatomical imaging with [18F]fluorodeoxyglucose utilizing a dual-head coincidence gamma camera with an integrated X-ray transmission system in non-small cell lung cancer.

AIM: To evaluate functional-anatomical imaging with 2-[F]fluoro-2-deoxy-D-glucose (F-FDG) utilizing a dual-head coincidence gamma camera with an integrated X-ray transmission system for attenuation correction, anatomical mapping, and image fusion compared to conventional diagnostics by computed tomography (CT) in non-small cell lung cancer (NSCLC). METHODS: Thirty-five patients with NSCLC underwent FDG imaging of the thoracic area using a dual-head coincidence gamma camera (DHC) with an integrated X-ray transmission system. State-of-the-art CT scans had been performed before. Whole-body dedicated FDG positron emission tomography (PET) was performed immediately prior to DHC. Staging by CT and DHC, and DHC with integrated image fusion (FDHC) were re-evaluated with regard to detectable lesions, correct anatomical diagnoses, and clinical impact. Results of DHC and PET were compared for analysis of limitations of DHC. RESULTS: One hundred and thirteen tumour lesions were identified by CT. DHC detected 128 lesions overall: 102 true positive CT lesions were confirmed, 25 additional lesions were detected which affected staging in eight patients, and one false positive lung lesion did not show up in DHC. Nine CT lesions were missed by DHC (lymph node and lung). PET detected 150 areas of focally enhanced uptake, delivering two false positive results (nuchal muscles, pneumonia). Final evaluation confirmed 148 malignant lesions. Compared to CT, the results of DHC changed staging or treatment in 8/35 patients (23%). Lesion detection by DHC was limited by tumour size and intensity of FDG uptake. Image fusion provided relevant clinical information in 9/35 patients (26%). CONCLUSION: Functional imaging in NSCLC with this dual-head gamma camera is superior to morphological imaging by CT, although inferior to dedicated PET imaging. Combined functional-anatomical imaging has the potential to improve staging and localization procedures before surgery or radiotherapy.

The role of [(18)F] FDG-PET, CT/MRI and tumor marker kinetics in the evaluation of post chemotherapy residual masses in metastatic germ cell tumors--prospects for management.

The purpose of this study was to assess the ability of [(18)F]FDG-PET, CT/MRI and serum tumor marker (TM) to predict the viability of residual masses after high-dose chemotherapy (HD-Ctx) in patients with metastatic germ cell tumors (GCT). In a prospective study, 60 residual tumors in 28 GCT patients were classified as viable/nonviable by FDG-PET, CT/MRI and TM levels. The results were validated either by histological examination of a resected mass and/or biopsy or by clinical/radiological follow-up for at least 6 months. There were no significant differences among the sensitivities observed with PET, CT/MRI and TM, but PET was significantly more specific than CT/MRI in predicting residual mass viability. TM showed the highest specificity. The highest accuracy in classification of residual tumors was achieved by a combination of PET, CT/MRI and TM (area under the ROC curve =0.91). All mature teratomas showed false-negative PET results with SUVs in the same range as necrosis. For classification of residual masses after HD-Ctx of metastatic GCT, [(18)F]FDG-PET is a valuable diagnostic method to complement the established procedures CT and TM. Positive PET results are highly correlated with the presence of viable tumor, but residual masses with negative PET findings still require resection. In cases of tumor progression diagnosed by CT and elevated TM, additional PET examinations are without benefit. PET seems useful in patients with stable disease or partial remission in CT/MRI and normalized TM as well as in marker-negative disease.