Low-dose computed tomography for the diagnosis of pneumonia in elderly patients: a prospective, interventional cohort study.

The diagnosis of pneumonia is challenging. Our objective was to assess whether low-dose computed tomography (LDCT) modified the probability of diagnosing pneumonia in elderly patients.We prospectively included patients aged over 65 years with a suspicion of pneumonia treated with antimicrobial therapy (AT). All patients had a chest radiograph and LDCT within 72 h of inclusion. The treating clinician assessed the probability of pneumonia before and after the LDCT scan using a Likert scale. An adjudication committee retrospectively rated the probability of pneumonia and was considered as the reference for diagnosis. The main outcome was the difference in the clinician's pneumonia probability estimates before and after LDCT and the proportion of modified diagnoses which matched the reference diagnosis (the net reclassification improvement (NRI)).A total of 200 patients with a median age of 84 years were included. After LDCT, the estimated probability of pneumonia changed in 90 patients (45%), of which 60 (30%) were downgraded and 30 (15%) were upgraded. The NRI was 8% (NRI event (-6%) + NRI non-event (14%)).LDCT modified the estimated probability of pneumonia in a substantial proportion of patients. It mostly helped to exclude a diagnosis of pneumonia and hence to reduce unnecessary AT.

Hybrid ultrasound-MR guided HIFU treatment method with 3D motion compensation.

PURPOSE: Treatments using high-intensity focused ultrasound (HIFU) in the abdominal region remain challenging as a result of respiratory organ motion. A novel method is described here to achieve 3D motion-compensated ultrasound (US) MR-guided HIFU therapy using simultaneous ultrasound and MRI. METHODS: A truly hybrid US-MR-guided HIFU method was used to plan and control the treatment. Two-dimensional ultrasound was used in real time to enable tracking of the motion in the coronal plane, whereas an MR pencil-beam navigator was used to detect anterior-posterior motion. Prospective motion compensation of proton resonance frequency shift (PRFS) thermometry and HIFU electronic beam steering were achieved. RESULTS: The 3D prospective motion-corrected PRFS temperature maps showed reduced intrascan ghosting artifacts, a high signal-to-noise ratio, and low geometric distortion. The k-space data yielded a consistent temperature-dependent PRFS effect, matching the gold standard thermometry within approximately 1°C. The maximum in-plane temperature elevation ex vivo was improved by a factor of 2. Baseline thermometry acquired in volunteers indicated reduction of residual motion, together with an accuracy/precision of near-harmonic referenceless PRFS thermometry on the order of 0.5/1.0°C. CONCLUSIONS: Hybrid US-MR-guided HIFU ablation with 3D motion compensation was demonstrated ex vivo together with a stable referenceless PRFS thermometry baseline in healthy volunteer liver acquisitions. Magn Reson Med 79:2511-2523, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Assessment of CT dose to the fetus and pregnant female patient using patient-specific computational models.

PURPOSE: This work provides detailed estimates of the foetal dose from diagnostic CT imaging of pregnant patients to enable the assessment of the diagnostic benefits considering the associated radiation risks. MATERIALS AND METHODS: To produce realistic biological and physical representations of pregnant patients and the embedded foetus, we developed a methodology for construction of patient-specific voxel-based computational phantoms based on existing standardised hybrid computational pregnant female phantoms. We estimated the maternal absorbed dose and foetal organ dose for 30 pregnant patients referred to the emergency unit of Geneva University Hospital for abdominal CT scans. RESULTS: The effective dose to the mother varied from 1.1 mSv to 2.0 mSv with an average of 1.6 mSv, while commercial dose-tracking software reported an average effective dose of 1.9 mSv (range 1.7-2.3 mSv). The foetal dose normalised to CTDIvol varies between 0.85 and 1.63 with an average of 1.17. CONCLUSION: The methodology for construction of personalised computational models can be exploited to estimate the patient-specific radiation dose from CT imaging procedures. Likewise, the dosimetric data can be used for assessment of the radiation risks to pregnant patients and the foetus from various CT scanning protocols, thus guiding the decision-making process. KEY POINTS: • In CT examinations, the absorbed dose is non-uniformly distributed within foetal organs. • This work reports, for the first time, estimates of foetal organ-level dose. • The foetal brain and skeleton doses present significant correlation with gestational age. • The conceptus dose normalised to CTDI vol varies between 0.85 and 1.63. • The developed methodology is adequate for patient-specific CT radiation dosimetry.

Ethylene vinyl alcohol copolymer for occlusion of specific portal branches during preoperative portal vein embolisation with n-butyl-cyanoacrylate.

OBJECTIVES: To evaluate the safety and efficacy of ethylene vinyl alcohol copolymer (EVOH) injection for selective occlusion of portal branches considered at risk for non-target embolisation during preoperative portal vein embolisation (PVE). METHODS: Twenty-nine patients (mean age, 57 ± 17 years) submitted to PVE with n-butyl-cyanoacrylate (NBCA) and additional EVOH for selected portal branches were retrospectively analysed. Indications for the use of EVOH and the selected portal branches were evaluated. Degree of hypertrophy of the future liver remnant (FLR) and kinetic growth were assessed by CT volumetry performed before and 3-6 weeks after PVE. Clinical outcome and histopathological analysis of portal veins occluded with EVOH were reviewed. RESULTS: EVOH was indicated intraoperatively for embolisation of selected portal branches that the operator reported at risk to provoke non-target embolisation with NBCA. Indications for the use of EVOH were embolisation of segment IV (n = 21), embolisation of segmental portal branches with early bifurcation (n = 7) and PVE in a 1-year-old girl with cystic hamartomas. All targeted portal branches were successfully embolised. There were no cases with non-target embolisation by EVOH. The degree of hypertrophy of the FLR was 14.3 ± 8.1% and the kinetic growth rate was 2.7 ± 1.8% per week. CONCLUSION: EVOH is safe and effective for embolisation of selected portal vein branches considered at risk for non-target embolisation. KEY POINTS: • EVOH is another effective liquid embolic agent for preoperative PVE. • EVOH is relatively simple to handle with a minimal risk of non-target embolisation. • During PVE, some portal branches considered complicated to occlude with NBCA may be efficiently embolised with EVOH.

Local recurrence of squamous cell carcinoma of the head and neck after radio(chemo)therapy: Diagnostic performance of FDG-PET/MRI with diffusion-weighted sequences.

PURPOSE: To determine the diagnostic performance of FDG-PET/MRI with diffusion-weighted imaging (FDG-PET/DWIMRI) for detection and local staging of head and neck squamous cell carcinoma (HNSCC) after radio(chemo)therapy. MATERIALS AND METHODS: This was a prospective study that included 74 consecutive patients with previous radio(chemo)therapy for HNSCC and in whom tumour recurrence or radiation-induced complications were suspected clinically. The patients underwent hybrid PET/MRI examinations with morphological MRI, DWI and FDG-PET. Experienced readers blinded to clinical/histopathological data evaluated images according to established diagnostic criteria taking into account the complementarity of multiparametric information. The standard of reference was histopathology with whole-organ sections and follow-up ≥24 months. Statistical analysis considered data clustering. RESULTS: The proof of diagnosis was histology in 46/74 (62.2%) patients and follow-up (mean ± SD = 34 ± 8 months) in 28/74 (37.8%). Thirty-eight patients had 43 HNSCCs and 46 patients (10 with and 36 without tumours) had 62 benign lesions/complications. Sensitivity, specificity, and positive and negative predictive value of PET/DWIMRI were 97.4%, 91.7%, 92.5% and 97.1% per patient, and 93.0%, 93.5%, 90.9%, and 95.1% per lesion, respectively. Agreement between imaging-based and pathological T-stage was excellent (kappa = 0.84, p < 0.001). CONCLUSION: FDG-PET/DWIMRI yields excellent results for detection and T-classification of HNSCC after radio(chemo)therapy. KEY POINTS: • FDG-PET/DWIMRI yields excellent results for the detection of post-radio(chemo)therapy HNSCC recurrence. • Prospective one-centre study showed excellent agreement between imaging-based and pathological T-stage. • 97.5% of positive concordant MRI, DWI and FDG-PET results correspond to recurrence. • 87% of discordant MRI, DWI and FDG-PET results correspond to benign lesions. • Multiparametric FDG-PET/DWIMRI facilitates planning of salvage surgery in the irradiated neck.

Impact of iterative reconstructions on objective and subjective emphysema assessment with computed tomography: a prospective study.

OBJECTIVES: To prospectively evaluate the impact of iterative reconstruction (IR) algorithms on pulmonary emphysema assessment as compared to filtered back projection (FBP). METHODS: One hundred ten unenhanced chest CT examinations were obtained on two different scanners. Image reconstructions from a single acquisition were done with different levels of IR and compared with FBP on the basis of the emphysema index (EI), lung volume and voxel densities. Objective emphysema assessment was performed with 3D software provided by each manufacturer. Subjective assessment of emphysema was performed as a blinded evaluation. Quantitative and subjective values were compared using repeated ANOVA analysis, Bland-Altman analysis and Kendall's coefficient of concordance (W). RESULTS: Lung volumes are stable on both units, throughout all IR levels (P ≥ 0.057). EI significantly decreases on both units with the use of any level of IR (P < 0.001). The highest levels of IR are responsible for a decrease of 33-36 % of EI. Significant differences in minimal lung density are found between the different algorithms (P < 0.003). Intra- and inter-reader concordance for emphysema characterisation is generally good (W ≥ 0.77 and W ≥ 0.86, respectively). CONCLUSIONS: Both commercially available IR algorithms used in this study significantly changed EI but did not alter visual assessment compared to standard FBP reconstruction at identical radiation exposure. KEY POINTS: • Objective quantification of pulmonary emphysema is sensitive to iterative reconstructions • Subjective evaluation of pulmonary emphysema is not influenced by iterative reconstructions • Consistency in reconstruction algorithms is of paramount importance for pulmonary emphysema monitoring.

Emergency assessment of patients with acute abdominal pain using low-dose CT with iterative reconstruction: a comparative study.

OBJECTIVES: To determine if radiation dose delivered by contrast-enhanced CT (CECT) for acute abdominal pain can be reduced to the dose administered in abdominal radiography (<2.5 mSv) using low-dose CT (LDCT) with iterative reconstruction algorithms. METHODS: One hundred and fifty-one consecutive patients requiring CECT for acute abdominal pain were included, and their body mass index (BMI) was calculated. CECT was immediately followed by LDCT. LDCT series was processed using 1) 40% iterative reconstruction algorithm blended with filtered back projection (LDCT-IR-FBP) and 2) model-based iterative reconstruction algorithm (LDCT-MBIR). LDCT-IR-FBP and LDCT-MBIR images were reviewed independently by two board-certified radiologists (Raters 1 and 2). RESULTS: Abdominal pathology was revealed on CECT in 120 (79%) patients. In those with BMI <30, accuracies for correct diagnosis by Rater 1 with LDCT-IR-FBP and LDCT-MBIR, when compared to CECT, were 95.4% (104/109) and 99% (108/109), respectively, and 92.7% (101/109) and 100% (109/109) for Rater 2. In patients with BMI ≥30, accuracies with LDCT-IR-FBP and LDCT-MBIR were 88.1% (37/42) and 90.5% (38/42) for Rater 1 and 78.6% (33/42) and 92.9% (39/42) for Rater 2. CONCLUSIONS: The radiation dose delivered by CT to non-obese patients with acute abdominal pain can be safely reduced to levels close to standard radiography using LDCT-MBIR. KEY POINTS: • LDCT-MBIR (<2.5 mSv) can be used to assess acute abdominal pain. • LDCT-MBIR (<2.5 mSv) cannot safely assess acute abdominal pain in obese patients. • LDCT-IR-FBP (<2.5 mSv) cannot safely assess patients with acute abdominal pain.

Fat suppression techniques for breast MRI: Dixon versus spectral fat saturation for 3D T1-weighted at 3 T.

OBJECTIVE: To compare two fat suppression techniques used for 3D T1-weighted sequence in breast MRI (magnetic resonance imaging), namely Dixon versus spectral fat saturation (fat sat). MATERIALS AND METHODS: All breast MRI examinations performed in a Philips 3 T unit between March 2013 and October 2015 including either a Dixon or a fat sat sequence were retrospectively analyzed. The examinations were subjectively evaluated by two independent experienced readers in a scale of 5 for overall quality of fat suppression, homogeneity of fat suppression, definition of anatomic structures and focal lesions, diagnostic confidence for axillary and internal mammary regions and the presence of artifacts, 1 corresponding to excellent and 5 to non-diagnostic quality. Contrast-to-noise-ratio (CNR) measurements for muscle and focal lesions were also performed. RESULTS: Overall 161 women (mean age 51.6 ± 12.0 years) underwent 189 MR examinations, 113 with the fat saturation and 76 with the Dixon sequence. Interobserver variability was good (kappa = 0.757). In all subjectively evaluated parameters, the Dixon sequence was superior to the fat sat (p < 0.05). Mean values of CNR for muscle and focal lesions were 9.98 (±4.2), 17.9 (±7.53) for the fat sat and 18.3 (±10.4) and 29.3 (±14.1) for the Dixon sequence, respectively (p < 0.001). CONCLUSION: 3D T1 Dixon sequence is superior to fat sat for dedicated breast MRI at 3 T, in terms of efficiency of fat suppression and image quality with the added advantage of optimal exploration of the axillary areas.

Clinical utility of 18F-FDG-PET/MR for preoperative breast cancer staging.

OBJECTIVE: To evaluate the performance of 18F-fluorodeoxyglucose (FDG) positron emission tomography magnetic resonance imaging (PET/MR) for preoperative breast cancer staging. METHODS: Preoperative PET/MR exams of 58 consecutive women with breast cancer were retrospectively reviewed. Histology and mean follow-up of 26 months served as gold standard. Four experienced readers evaluated primary lesions, lymph nodes and distant metastases with contrast-enhanced MRI, qualitative/quantitative PET, and combined PET/MR. ROC curves were calculated for all modalities and their combinations. RESULTS: The study included 101 breast lesions (83 malignant, 18 benign) and 198 lymph node groups, (34 malignant, 164 benign). Two patients had distant metastases. Areas under the curve (AUC) for breast cancer were 0.9558, 0.8347 and 0.8855 with MRI, and with qualitative and quantitative PET/MR, respectively (p = 0.066). Sensitivity for primary cancers with MRI and quantitative PET/MR was 100 % and 77 % (p = 0.004), and for lymph nodes 88 % and 79 % (p = 0.25), respectively. Specificity for MRI and PET/MR for primary cancers was 67 % and 100 % (p = 0.03) and for lymph nodes 98 % and 100 % (p = 0.25). CONCLUSIONS: In breast cancer patients, MRI alone has the highest sensitivity for primary tumours. For nodal metastases, both MRI and PET/MR are highly specific. KEY POINTS: • MRI alone and PET/MR have a similar overall diagnostic performance. • MRI alone has a higher sensitivity than PET/MR for local tumour assessment. • Both MRI and PET/MR have a limited sensitivity for nodal metastases. • Positive lymph nodes on MRI or PET/MR do not require presurgical biopsy.

Emergency Computed Tomography: What is Missed at First Reading?

OBJECTIVES: The aim of this study was to evaluate the accuracy of preliminary computed tomography (CT) interpretations made by radiology residents in the emergency department. METHODS: For 4 periods of 20 consecutive days, attending radiologists prospectively recorded any disparities between their own CT interpretations (reference standard) and the preliminary interpretations of emergency radiology residents. Misinterpretations were defined as major when related to a potentially life-threatening pathology if not immediately managed after CT. The rate of disparities was calculated for all CT examinations, separately for body and neuroradiological cases, and for working and on-call hours. RESULTS: A total of 3044 emergency CT examinations were performed during the survey: 1568 (51%) body scans and 1476 (49%) neurological scans. Disparities were reported in 145 (4.8%) of all CT examinations, with 0.8% (24/3044) defined as major misinterpretations. There were 100 (6.3%) of 1568 disparities in body CT versus 45 (3.0%) of 1476 in neurological CT examinations (P = 0.001). No significant differences were found between disparities recorded during regular working hours (47/1083 [4.3%]) versus on-call hours (98/1961 [5.0%], P = 0.47). CONCLUSIONS: There were typically more disparities between resident and attending interpretations in emergency body CT. Major disparities represented only a small proportion of all misinterpretations. The detailed analysis of our data enables benchmarking over time and offers a reference for optimizing the training of residents in emergency radiology.

Illegal intra-corporeal packets: can dual energy CT be used for the evaluation of cocaine concentration? A cross sectional study.

BACKGROUND: The recent implementation of the dual energy technology on CT-scanners has opened new perspectives in tissue and material characterization. This study aims to evaluate whether dual energy CT can be used to assess the concentration of cocaine of intra-intestinal illegal packets. METHODS: The study was approved by the institutional review board of our institution (CER 13_027_R). From November 2010 to May 2013, all consecutive conveyors in whom a low-dose abdominal CT (LDCT) revealed the presence of illegal intra-corporeal drug packets underwent a dual energy CT series (gemstone spectral imaging) targeted on one container. The mean radiological density (HU) of these packets was measured on the LDCT series, and on the monochromatic dual energy series, at 40 and 140 keV. The difference between the HU at 40 and 140 keV was reported as ∆HU. The effective atomic number Z(eff) was also measured on the monochromatic series. A chemical analysis was performed after expulsion to select cocaine containing packets, and to determine their cocaine concentrations. A correlation analysis was performed between HU, ∆HU and Z(eff), with regard to the percentage of cocaine. RESULTS: Fifty-four cocaine conveyors were included. The mean cocaine content of the packets was 36.8% (range 11.2-80, SD 15.4), the mean radiologic density 105 HU, the mean Z(eff) 8.7 and the mean ∆HU 163. The cocaine content was correlated with the ∆HU (0.57, p < 0.001), with the Z(eff) (r = 0.56, p < 0.001) but not with radiologic density (r = 0.25, p = 0.064). ∆HU >200 was 0.9 (9 of 10) sensitive and 0.82 (36 of 44) specific to predict a cocaine concentration higher than 50%. CONCLUSION: Measuring ∆HU or Z(eff) on dual energy monochromatic CT series can be used to detect ingested packets with cocaine concentration >50%.

Image quality of low mA CT pulmonary angiography reconstructed with model based iterative reconstruction versus standard CT pulmonary angiography reconstructed with filtered back projection: an equivalency trial.

OBJECTIVE: To determine whether CT pulmonary angiography (CTPA) using low mA setting reconstructed with model-based iterative reconstruction (MBIR) is equivalent to routine CTPA reconstructed with filtered back projection (FBP). METHODS: This prospective study was approved by the institutional review board and patients provided written informed consent. Eighty-two patients were examined with a low mA MBIR-CTPA (100 kV, 20 mA) and 82 patients with a standard FBP-CTPA (100 kV, 250 mA). Region of interests were drawn in nine pulmonary vessels; signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. A five-point scale was used to subjectively evaluate the image quality of FBP-CTPA and low mA MBIR-CTPA. RESULTS: Compared to routine FBP-CTPA, low mA MBIR-CTPA showed no differences in the attenuation measured in nine pulmonary vessels, higher SNR (56 ± 19 vs 43 ± 20, p < 0.0001) and higher CNR (50 ± 17 vs 38 ± 18, p < 0.0001) despite a dose reduction of 93 % (p < 0.0001). The subjective image quality of low mA MBIR-CTPA was quoted as diagnostic in 98 % of the cases for patient with body mass index less than 30 kg/m(2). CONCLUSION: Low mA MBIR-CTPA is equivalent to routine FBP-CTPA and allows a significant dose reduction while improving SNR and CNR in the pulmonary vessels, as compared with routine FBP-CTPA. KEY POINTS: • Low mA MBIR-CTPA is equivalent to routine FBP-CTPA. • MBIR-CTPA may be achieved with drastic (93 %) dose reduction. • Low mA MBIR-CTPA should be studied in the setting of suspected PE.

Spatio-temporal quantitative thermography of pre-focal interactions between high intensity focused ultrasound and the rib cage.

OBJECTIVE: The aim of this paper is to quantitatively investigate the thermal effects generated by the pre-focal interactions of a HIFU beam with a rib cage, in the context of minimally invasive transcostal therapy of liver malignancies. MATERIALS AND METHODS: HIFU sonications were produced by a phased-array MR-compatible transducer on Turkey muscle placed on a sheep thoracic cage specimen. The thoracic wall was positioned in the pre-focal zone 3.5 to 6.5 cm below the focus. Thermal monitoring was simultaneously performed using fluoroptic sensors inserted into the medullar cavity of the ribs and high resolution MR-thermometry (voxel: 1 × 1 × 5 mm3, four multi-planar slices). RESULTS: MR-thermometry data indicated nearly isotropic distribution of the thermal energy at the ribs' surface. The temperature elevation at the focus was comparable with the pericostal temperature elevation around unprotected ribs, while being systematically inferior, by more than a factor of four on average, to the intra-medullar values. The spatial profiles of the pericostal and intra-medullar thermal build-up measurements could be smoothly connected using a Gaussian function. The dynamics of the post-sonication thermal relaxation as determined by fluoroptic measurements was demonstrated to be theoretically coherent with the experimental observations. CONCLUSION: The experimental findings motivate further efforts for the transfer towards clinical routine of effective rib-sparing strategies for hepatic HIFU.

Hepatic lymphatics: anatomy and related diseases.

The liver normally produces a large amount of lymph. It is estimated that between 25% and 50% of the lymph received by the thoracic duct comes from the liver. In normal conditions, hepatic lymphatics are not depicted on cross-sectional imaging. They are divided in lymphatics of deep system (lymphatics following the hepatic veins and the portal tract) and those of superficial system (convex surface and inferior surface). A variety of diseases may affect hepatic lymphatics and in general they manifest as lymphedema, lymphatic mass, or cystic lesions. Abnormal distended lymphatics are especially seen in periportal spaces as linear hypoattenuations on CT or strong linear hyperintensities on heavily T2-weighted MR imaging. Lymphatic tumor spread as in lymphoma and lymphangitic carcinomatosis manifests as periportal masses and regional lymph node enlargement. Lymphatic disruption after trauma or surgery is depicted as perihepatic fluid collections of lymph (lymphocele). Lymphatic malformation such as lymphangioma is seen on imaging as cystic spaces of variable size.

An experimental model to investigate the targeting accuracy of MR-guided focused ultrasound ablation in liver.

BACKGROUND: Magnetic Resonance-guided High Intensity Focused Ultrasound (MRgHIFU) is a hybrid technology that aims to offer non-invasive thermal ablation of targeted tumors or other pathological tissues. Acoustic aberrations and non-linear wave propagating effects may shift the focal point significantly away from the prescribed (or, theoretical) position. It is therefore mandatory to evaluate the spatial accuracy of ablation for a given HIFU protocol and/or device. We describe here a method for producing a user-defined ballistic target as an absolute reference marker for MRgHIFU ablations. METHODS: The investigated method is based on trapping a mixture of MR contrast agent and histology stain using radiofrequency (RF) ablation causing cell death and coagulation. A dedicated RF-electrode was used for the marker fixation as follows: a RF coagulation (4 W, 15 seconds) and injection of the mixture followed by a second RF coagulation. As a result, the contrast agent/stain is encapsulated in the intercellular space. Ultrasonography imaging was performed during the procedure, while high resolution T1w 3D VIBE MR acquisition was used right after to identify the position of the ballistic marker and hence the target tissue. For some cases, after the marker fixation procedure, HIFU volumetric ablations were produced by a phased-array HIFU platform. First ex vivo experiments were followed by in vivo investigation on four rabbits in thigh muscle and six pigs in liver, with follow-up at Day 7. RESULTS: At the end of the procedure, no ultrasound indication of the marker's presence could be observed, while it was clearly visible under MR and could be conveniently used to prescribe the HIFU ablation, centered on the so-created target. The marker was identified at Day 7 after treatment, immediately after animal sacrifice, after 3 weeks of post-mortem formalin fixation and during histology analysis. Its size ranged between 2.5 and 4 mm. CONCLUSIONS: Experimental validation of this new ballistic marker method was performed for liver MRgHIFU ablation, free of any side effects (e.g. no edema around the marker, no infection, no bleeding). The study suggests that the absolute reference marker had ultrasound conspicuity below the detection threshold, was irreversible, MR-compatible and MR-detectable, while also being a well-established histology staining technique.

Detection and quantification of focal uptake in head and neck tumours: (18)F-FDG PET/MR versus PET/CT.

PURPOSE: Our objectives were to assess the quality of PET images and coregistered anatomic images obtained with PET/MR, to evaluate the detection of focal uptake and SUV, and to compare these findings with those of PET/CT in patients with head and neck tumours. METHODS: The study group comprised 32 consecutive patients with malignant head and neck tumours who underwent whole-body (18)F-FDG PET/MR and PET/CT. PET images were reconstructed using the attenuation correction sequence for PET/MR and CT for PET/CT. Two experienced observers evaluated the anonymized data. They evaluated image and fusion quality, lesion conspicuity, anatomic location, number and size of categorized (benign versus assumed malignant) lesions with focal uptake. Region of interest (ROI) analysis was performed to determine SUVs of lesions and organs for both modalities. Statistical analysis considered data clustering due to multiple lesions per patient. RESULTS: PET/MR coregistration and image fusion was feasible in all patients. The analysis included 66 malignant lesions (tumours, metastatic lymph nodes and distant metastases), 136 benign lesions and 470 organ ROIs. There was no statistically significant difference between PET/MR and PET/CT regarding rating scores for image quality, fusion quality, lesion conspicuity or anatomic location, number of detected lesions and number of patients with and without malignant lesions. A high correlation was observed for SUVmean and SUVmax measured on PET/MR and PET/CT for malignant lesions, benign lesions and organs (ρ = 0.787 to 0.877, p < 0.001). SUVmean and SUVmax measured on PET/MR were significantly lower than on PET/CT for malignant tumours, metastatic neck nodes, benign lesions, bone marrow, and liver (p < 0.05). The main factor affecting the difference between SUVs in malignant lesions was tumour size (p < 0.01). CONCLUSION: In patients with head and neck tumours, PET/MR showed equivalent performance to PET/CT in terms of qualitative results. Comparison of SUVs revealed an excellent correlation for measurements on both modalities, but underestimation of SUVs measured on PET/MR as compared to PET/CT.

Urinary stone detection and characterisation with dual-energy CT urography after furosemide intravenous injection: preliminary results.

OBJECTIVES: To investigate the added advantage of IV furosemide injection and the subsequent urine dilution in the detection of urinary calculi in the excretory phase of dual-source dual-energy (DE) computed tomography (CT) urography, and to investigate the feasibility of characterising the calculi through diluted urine. METHODS: Twenty-three urinary calculi were detected in 116 patients who underwent DECT urography for macroscopic haematuria with a split bolus two- or three-acquisition protocol, including a true unenhanced series and at least a mixed nephrographic excretory phase. Virtual unenhanced images were reconstructed from contrast-enhanced DE data. Calculi were recorded on all series and characterised based on their X-ray absorption characteristics at 100 kVp and 140 kVp in both true unenhanced and nephrographic excretory phase series. RESULTS: All calculi with a diameter more than 2 mm were detected in the virtual unenhanced phase and in the nephrographic excretory phase. Thirteen of these calculi could be characterised in the true unenhanced phase and in the mixed nephrographic excretory phase. The results were strictly identical for both phases, six of them being recognised as non-uric acid calculi and seven as uric acid calculi. CONCLUSIONS: Mixed nephrographic excretory phase DECT after furosemide administration allows both detection and characterisation of clinically significant calculi, through the diluted urine. KEY POINTS: • Urinary tract stones can be detected on excretory phase through diluted urine. • Urinary tract stone characterisation with dual-energy CT (DECT) is possible through diluted urine. • A dual energy split-bolus CT urography simultaneously enables urinary stone detection and characterisation.

Diagnosis of urothelial tumors with a dedicated dual-source dual-energy MDCT protocol: preliminary results.

OBJECTIVE: The purpose of this study was to evaluate the diagnostic performance of a dedicated dual-source dual-energy MDCT (DECT) protocol for the detection of urothelial tumors. MATERIALS AND METHODS: A DECT protocol including furosemide and split-bolus contrast injection was used in 69 consecutive patients with suspected abnormalities of the urinary system. Thirteen patients were excluded because there was no follow-up available. In 56 patients, the final diagnosis was proven with endoscopy, biopsy, or follow-up and included urothelial tumors (n = 37) in 16 patients, other urinary tract pathologies (n = 9) in eight patients, and absence of lesions of the collecting system in 32 patients. The image series consisted of a dual-energy true unenhanced series, 35-second arterial phase, and 8-minute nephrographic-excretory phase and were analyzed retrospectively. True enhancement of all detected lesions was measured. On the basis of the DECT data of the contrast-enhanced images, virtual unenhanced series were created and iodine concentration was calculated using commercially available software. The attenuation difference between virtual unenhanced and contrast-enhanced images (virtual enhancement) was measured. CT findings were compared with the final diagnosis. RESULTS: Urothelial tumors were identified on 35-second series, 8-minute series, and both series combined, with sensitivity of 91.9% (95% CI, 78.1-98.2%), 83.4% (68.0-93.8%), and 97.3% (85.8-100%), respectively. Urothelial tumors showed stronger virtual enhancement (p = 0.02) and higher iodine concentration (p = 0.03) than lesions of other origin. Distinction between urothelial tumors and nontumoral lesions was possible with sensitivity of 91.9% (78.1-98.2%) when using a threshold concentration of at least 1.0 mg I/mL. CONCLUSION: Dual phase DECT with virtual unenhanced imaging and iodine concentration measurement appears to be a useful diagnostic test for urothelial tumors.

Model-based iterative reconstruction versus adaptive statistical iterative reconstruction in low-dose abdominal CT for urolithiasis.

OBJECTIVE: The purpose of this study was to determine whether there is added benefit to model-based iterative reconstruction as compared with adaptive statistical iterative reconstruction on low-dose abdominal CT in the clinical context of known or suspected urolithiasis. MATERIALS AND METHODS: Fifty-three consecutive patients (35 men, 18 women; mean [SD] age, 52.3 ± 16.6 years) underwent unenhanced low-dose abdominal CT for detection or follow-up of urinary tract stones. Ureteral definition was evaluated subjectively by two blinded readers who scored it from 1 (excellent definition) to 4 (not distinguishable) and objectively by calculating contrast-to-noise ratio (CNR) for soft tissue and fat on a standard 40% adaptive statistical iterative reconstruction and on the corresponding model-based iterative reconstruction series. The position, maximal density, and diameter on the axial plane of stones were also evaluated on both series. RESULTS: There was an almost perfect agreement (κ = 0.872) between readers for subjective evaluation of ureteral definition. The ureteral definition was significantly better for the model-based iterative reconstruction series (mean [SD] score, 1.998 ± 0.839) compared with adaptive statistical iterative reconstruction (mean score, 2.536 ± 0.799) (p < 0.0001). Mean CNR was significantly better on the model-based iterative reconstruction (17.82 ± 4.84) compared with adaptive statistical iterative reconstruction (6.066 ± 1.985) (p < 0.0001). Sixty-nine stones were found in total. Their maximal density measured from model-based iterative reconstruction was significantly higher (754.4 ± 376.5 HU) than that measured from adaptive statistical iterative reconstruction (559.4 ± 352.4 HU) (p < 0.0001). Size of stones was overevaluated on model-based iterative reconstruction (mean diameter, 4.91 ± 2.61 mm) compared with adaptive statistical iterative reconstruction (4.52 ± 2.63 mm) (p < 0.0001). CONCLUSION: Model-based iterative reconstruction of low-dose abdominal CT can offer significantly better ureteral definition than adaptive statistical iterative reconstruction, and its systematic use could thus be recommended. However, it has the tendency to systematically overevaluate the stones' densities and sizes.