[18F]FDG Positron emission tomography with whole body magnetic resonance imaging ([18F]FDG-PET/MRI) as a diagnosis tool in Schwannomatosis

Schwannomatosis is a rare autosomal dominant genetic syndrome characterized by the presence of multiple schwannomas. The main symptom is neurogenic pain. The diagnosis requires the presence of several schwannomas and whole-body ^[18F]FDG-PET/MRI might help detect extra schwannomas in patients when the diagnosis is uncertain. Among the 25 patients treated for Schwannomatosis in our tertiary center, three men and two women had had a ^[18F]FDG-PET/MRI performed, and the number of schwannomas detected by ^[18F]FDG-PET/MRI outnumbered the number of schwannomas suspected during the clinical examination. The majority of schwannomas exhibited a radiolabeling (median of 66.7%, range 28-93%). Our findings show that ^[18F]FDG-PET/MRI could prove useful when suspecting schwannomatosis to accelerate diagnosis and offer optimal care to patients.

Prediction of overall survival in patients with hepatocellular carcinoma treated with Y-90 radioembolization by imaging response criteria

PURPOSE

To evaluate the potential of imaging criteria in predicting overall survival of patients with hepatocellular carcinoma (HCC) after a first transcatheter arterial yttrium-90 radioembolization (TARE) MATERIALS AND METHODS: From October 2013 to July 2017, 37 patients with HCC were retrospectively included. There were 34 men and 3 women with a mean age of 60.5±10.2 (SD) years (range: 32.7-78.9 years). Twenty-five patients (68%) were Barcelona Clinic Liver Cancer (BCLC) C and 12 (32%) were BCLC B. Twenty-four primary index tumors (65%) were>5cm. Three radiologists evaluated tumor response on pre- and 4-7 months post-TARE magnetic resonance imaging or computed tomography examinations, using Response Evaluation Criteria in Solid Tumors (RECIST) 1.1, modified RECIST (mRECIST), European Association for Study of the Liver (EASL), volumetric RECIST (vRECIST), quantitative EASL (qEASL) and the Liver Imaging Reporting and Data System treatment response algorithm. Kaplan-Meier survival curves were used to compare responders and non-responders for each criterion. Univariate and multivariate Cox proportional hazard ratio (HR) analysis were used to identify covariates associated with overall survival. Fleiss kappa test was used to assess interobserver agreement.

RESULTS

At multivariate analysis, RECIST 1.1 (HR: 0.26; 95% confidence interval [95% CI]: 0.09-0.75; P=0.01), mRECIST (HR: 0.22; 95% CI: 0.08-0.59; P=0.003), EASL (HR: 0.22; 95% CI: 0.07-0.63; P=0.005), and qEASL (HR: 0.30; 95% CI: 0.12-0.80; P=0.02) showed a significant difference in overall survival between responders and nonresponders. RECIST 1.1 had the highest interobserver reproducibility.

CONCLUSION

RECIST and mRECIST seem to be the best compromise between reproducibility and ability to predict overall survival in patients with HCC treated with TARE.

Iterative reconstructions in multiphasic CT imaging of the liver: qualitative and task-based analyses of image quality

AIM

To evaluate the clinical benefits on image quality (IQ) of adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR) in multiphasic liver CT compared to filtered back-projection (FBP), in patients and on phantoms using a novel task-based metric.

MATERIALS AND METHODS

Image data of 65 patients who underwent a routine multiphasic liver CT during a 1-month period were reconstructed with FBP, ASIR50, ASIR80, and MBIR. IQ was assessed qualitatively by ranking the most distal hepatic artery (HA) and portal vein (PV) visible; and quantitatively by measuring contrast-to-noise ratio (CNR) of the liver parenchyma, HA and PV. IQ was compared between each reconstruction and correlated to CNR and detectability index (d') measurements computed on phantoms scanned with the same CT protocol as for patients.

RESULTS

HA and PV were seen more distally on MBIR and ASIR80 compared to FBP (p≤0.001). The CNR correlated weakly between patient and phantom (r=0.76 and 0.80 for HA and PV, respectively), whereas d' correlated strongly with the division order of HA and PV (r=0.96 and 0.95, respectively).

CONCLUSION

MBIR and ASIR significantly improve the IQ of multiphasic liver CT, especially through better distal detection of HA and PV, in agreement with the adapted task-based metric d' estimated on phantoms.

Measurement variability of liver metastases from neuroendocrine tumors on different magnetic resonance imaging sequences

PURPOSE

To assess dimension measurement variability of liver metastases from neuroendocrine tumors (LMNET) on different magnetic resonance imaging (MRI) sequences.

MATERIAL AND METHODS

In this institutional review board-approved retrospective study from January 2011 to December 2012, all liver MRI examinations performed at our department in patients with at least one measurable LMNET according to response evaluation criteria in solid tumors (RECIST1.1) were included. Up to two lesions were selected on T2-weighted MR images. Three reviewers independently measured long axes of 135 hepatic metastases in 30 patients (16 men, 14 women, mean age 61±11.4 (SD) years; range 28-78 years), during two separate reading sessions, on T2-weighted, diffusion-weighted MRI (DWI) (b; 50, 400, 800 s/mm²) and arterial, portal and late phases after intravenous administration of a gadolinium chelate. Intraclass-correlation coefficients and Bland-Altman plots were used to assess intra-and interobserver variability.

RESULTS

Intra- and interobserver agreements ranged between 0.87-0.98, and 0.88-0.97, respectively. Intersequence agreements ranged between 0.92 [95%CI: 0.82-0.98] and 0.98 [95%CI: 0.93-0.99]. 95% limits of agreement for measurements were -10.2%,+8.9% for DWI (b=50s/mm²) versus -21.9%,+24.2% and -15.8,+17.2% for arterial and portal phases, respectively.

CONCLUSION

An increase<9% in measurement and a decrease of -10% on DWI should not be considered as true changes, with 95% confidence, versus 24% and -22% on arterial and 17%, -16% on portal phases, respectively. DWI might thus be the most reliable MR sequence for monitoring size variations of LMNETs.

Imaging of the postoperative liver: review of normal appearances and common complications

Several benign and malignant liver diseases may require surgical treatment for cure, including anatomical resections based on the segmental anatomy of the liver, non-anatomical (wedge) resections, and surgical management of biliary cysts. The type of surgery depends not only on the location and the nature of the disease, but also on the expertise of the surgeon. Whereas ultrasonography is often the first-line imaging examination in case of suspected postoperative complication, multidetector computed tomography (MDCT) is of greater value for identifying normal findings after surgery, early postoperative pathologic fluid collections and vascular thromboses, and tumor recurrence in patients who have undergone hepatic surgery. Magnetic resonance cholangiopancreatography (MRCP) is the imaging modality of choice for depicting early postoperative bile duct injuries and ischemic cholangitis that may occur in the late postoperative phase. Both MDCT and MRCP can accurately depict tumor recurrence. Radiologists should become familiar with these surgical procedures to better understand postoperative changes, and with the normal imaging appearances of various postoperative complications to better differentiate between complications and normal findings.

An automatic respiratory gating method for the improvement of microcirculation evaluation: application to contrast-enhanced ultrasound studies of focal liver lesions

Contrast-enhanced ultrasound (CEUS), with the recent development of both contrast-specific imaging modalities and microbubble-based contrast agents, allows noninvasive quantification of microcirculation in vivo. Nevertheless, functional parameters obtained by modeling contrast uptake kinetics could be impaired by respiratory motion. Accordingly, we developed an automatic respiratory gating method and tested it on 35 CEUS hepatic datasets with focal lesions. Each dataset included fundamental mode and cadence contrast pulse sequencing (CPS) mode sequences acquired simultaneously. The developed method consisted in (1) the estimation of the respiratory kinetics as a linear combination of the first components provided by a principal components analysis constrained by a prior knowledge on the respiratory rate in the frequency domain, (2) the automated generation of two respiratory-gated subsequences from the CPS mode sequence by detecting end-of-inspiration and end-of-expiration phases from the respiratory kinetics. The fundamental mode enabled a more reliable estimation of the respiratory kinetics than the CPS mode. The k-means algorithm was applied on both the original CPS mode sequences and the respiratory-gated subsequences resulting in clustering maps and associated mean kinetics. Our respiratory gating process allowed better superimposition of manually drawn lesion contours on k-means clustering maps as well as substantial improvement of the quality of contrast uptake kinetics. While the quality of maps and kinetics was satisfactory in only 11/35 datasets before gating, it was satisfactory in 34/35 datasets after gating. Moreover, noise amplitude estimated within the delineated lesions was reduced from 62 ± 21 to 40 ± 10 (p < 0.01) after gating. These findings were supported by the low residual horizontal (0.44 ± 0.29 mm) and vertical (0.15 ± 0.16 mm) shifts found during manual motion correction of each respiratory-gated subsequence. The developed technique could be used as a basis for accurate quantification of perfusion parameters for the evaluation and follow-up of patients under antiangiogenic therapies.

Renal blood flow quantification in pigs using contrast-enhanced ultrasound: an ex vivo study

PURPOSE

The aim of the study was to evaluate a new method for the quantification of renal blood flow using contrast-enhanced ultrasound (CEUS) in an ex vivo pig kidney model.

MATERIAL AND METHODS

After approval by the animal ethics committee, 4 pig kidneys were explanted and perfused with Celsior liquid (Imtix Sangstat, Lyon, France) at different flow rates (30, 50, 70 and 90 ml/min) in an ex vivo phantom. A 50 % diluted solution of SonoVue (Bracco, Milano, Italy) was infused in the artery at 0.5 ml/min. CEUS was performed with an Aplio system (Toshiba, Nasu, Japan) using a broadband linear transducer and pulse subtraction imaging. A total of 152 destruction-reperfusion sequences were acquired and cine loops were digitally stored for further quantification. Three different ROIs were placed upon the anterior, posterior cortex and segmental artery. Signal intensity measurements were performed in linear units and perfusion parameters were automatically extracted using dedicated software. Curve fitting was performed using a monoexponential model in which a time delay parameter was introduced. This fit allowed the assessment of the local blood flow into the region of interest (called "contrast-enhanced blood flow" (CEBF)). The artery mean signal intensity was averaged from the ten frames prior to the destruction phase. The normalized CEBF (nCEBF) was calculated as the ratio between CEBF and the mean arterial signal intensity. The CEBF and nCEBF were compared to the true blood flow indicated by the pump flow rate.

RESULTS

The CEBF was correlated to the true blood flow only for the posterior cortical ROI (R(2) = 0.45, p = 0.05). The normalization using arterial signals improved CEBF correlation to true blood flow: nCEBF became correlated to the true blood flow when considering all ROIs (R(2)= 0.94, p < 0.0001) and correlation was improved for both anterior and posterior cortical ROIs (R(2)= 0, 93, p = 0.0004; R(2)= 0, 90, p = 0.0005, respectively). However, a significant kidney-dependent effect was observed for the anterior cortical ROI (p = 0.017) but not for the posterior cortical ROI (p = 0.89).

CONCLUSION

Normalization using arterial signals significantly improved the estimation of blood flow calculated with CEUS.

[Tissue attenuation in small animals on contrast enhanced ultrasound]

Despite recent advances in contrast-enhanced ultrasound imaging, evaluation of tissue perfusion with contrast-enhanced ultrasound is still impaired by shadowing effects. These effects are particularly relevant in small animal studies due to high frequency imaging. Current methods of tissue attenuation correction are not suited for contrast-enhanced ultrasound examinations, because microbubble acoustic response to ultrasound waves is far more complex than that of tissues. A method allowing in vivo tissue attenuation correction in the presence of contrast agents is presented.

Methadone dose, plasma level, and cross-tolerance to heroin in man

The development of cross-tolerance between methadone and heroin was studied in postaddict volunteers who had been drug-free for at least 6 weeks. Two methadone dose schedules were used; each was employed in six subjects. One schedule brought the subjects to a dose of 40 mg, while the other brought them to 80 mg of methadone a day. Subjects received injections of heroin (0.214 mg/kg) and placebo at various times before and during methadone treatment. Pupillary and subjective effects of injections were measured. Plasma levels of methadone were determined concurrently. Subjects on both treatment schedules developed an incomplete cross-tolerance to this dose of heroin. As the dose and plasma level of methadone increased with time, the cross-tolerance to all heroin effects increased. Plasma levels did not affect the development of cross-tolerance independently of methadone dose. The most important contribution to the cross-tolerance to pupillary effects was made by the duration of methadone treatment. Furthermore, the cross-tolerance to the subjective effects of heroin developed earlier than that to the pupil effect.

Methadone in man: pharmacokinetic and excretion studies in acute and chronic treatment

The biologic disposition of methadone in acute and during chronic administration was studied in 12 human volunteers. In the acute study a biexponential methadone plasma level decay was observed. The acute primary half-life (t1/2) of 14.3 hr in combination with the acute secondary t1/2 of 54.8 hr were longer than the single exponential chronic t1/2 of 22.2 hr determined in the same subjects. The urinary and fecal excretion of methadone and its mono-N-demethylated metabolite increased from 22.2% in the acute to 62.0% in the chronic phase of the study. The urinary metabolite 1 to methadone ratio tripled from the acute to the chronic phase. The pupillary effects of methadone monitored throughout 24 hr were nearly the same in magnitude in the acute and the chronic studies, whereas the plasma levels increased 3- to 8-fold following chronic methadone administration. These findings suggest that both dispositional and pharmacologic tolerance are involved in the development of tolerance following chronic administration of methadone.