Cross-dimensional transfer learning in medical image segmentation with deep learning.

Over the last decade, convolutional neural networks have emerged and advanced the state-of-the-art in various image analysis and computer vision applications. The performance of 2D image classification networks is constantly improving and being trained on databases made of millions of natural images. Conversely, in the field of medical image analysis, the progress is also remarkable but has mainly slowed down due to the relative lack of annotated data and besides, the inherent constraints related to the acquisition process. These limitations are even more pronounced given the volumetry of medical imaging data. In this paper, we introduce an efficient way to transfer the efficiency of a 2D classification network trained on natural images to 2D, 3D uni- and multi-modal medical image segmentation applications. In this direction, we designed novel architectures based on two key principles: weight transfer by embedding a 2D pre-trained encoder into a higher dimensional U-Net, and dimensional transfer by expanding a 2D segmentation network into a higher dimension one. The proposed networks were tested on benchmarks comprising different modalities: MR, CT, and ultrasound images. Our 2D network ranked first on the CAMUS challenge dedicated to echo-cardiographic data segmentation and surpassed the state-of-the-art. Regarding 2D/3D MR and CT abdominal images from the CHAOS challenge, our approach largely outperformed the other 2D-based methods described in the challenge paper on Dice, RAVD, ASSD, and MSSD scores and ranked third on the online evaluation platform. Our 3D network applied to the BraTS 2022 competition also achieved promising results, reaching an average Dice score of 91.69% (91.22%) for the whole tumor, 83.23% (84.77%) for the tumor core and 81.75% (83.88%) for enhanced tumor using the approach based on weight (dimensional) transfer. Experimental and qualitative results illustrate the effectiveness of our methods for multi-dimensional medical image segmentation.

Frontline thrombectomy strategy and outcome in acute basilar artery occlusion.

BACKGROUND: Novel thrombectomy strategies emanate expeditiously day-by-day counting on access system, clot retriever device, proximity to and integration with the thrombus, and microcatheter disengagement. Nonetheless, the relationship between native thrombectomy strategies and revascularization success remains to be evaluated in basilar artery occlusion (BAO). PURPOSE: To compare the safety and efficacy profile of key frontline thrombectomy strategies in BAO. METHODS: Retrospective analyses of prospectively maintained stroke registries at two comprehensive stroke centers were performed between January 2015 and December 2019. Patients with BAO selected after MR imaging were categorized into three groups based on the frontline thrombectomy strategy (contact aspiration (CA), stent retriever (SR), or combined (SR+CA)). Patients who experienced failure of clot retrieval followed by an interchanging strategy were categorized as a fourth (switch) group. Clinicoradiological features and procedural variables were compared. The primary outcome measure was the rate of complete revascularization (modified Thrombolysis in Cerebral Infarction (mTICI) grade 2c-3). Favorable outcome was defined as a 90 day modified Rankin Scale score of 0-2. RESULTS: Of 1823 patients, we included 128 (33 underwent CA, 35 SR, 35 SR +CA, and 25 switch techniques). Complete revascularization was achieved in 83/140 (59%) primarily analyzed patients. SR +CA was associated with higher odds of complete revascularization (adjusted OR 3.04, 95% CI 1.077 to 8.593, p=0.04) which was an independent predictor of favorable outcome (adjusted OR 2.73. 95% CI 1.152 to 6.458, p=0.02). No significant differences were observed for symptomatic intracranial hemorrhage, functional outcome, or mortality rate. CONCLUSION: Among BAO patients, the combined technique effectively contributed to complete revascularization that showed a 90 day favorable outcome with an equivalent complication rate after thrombectomy.

Radiotherapy Target Volume Definition in Newly Diagnosed High-Grade Glioma Using 18F-FET PET Imaging and Multiparametric MRI: An Inter Observer Agreement Study.

Background: The aim of this prospective monocentric study was to assess the inter-observer agreement for tumor volume delineations by multiparametric MRI and 18-F-FET-PET/CT in newly diagnosed, untreated high-grade glioma (HGG) patients. Methods: Thirty patients HGG underwent O-(2-[18F]-fluoroethyl)-l-tyrosine(18F-FET) positron emission tomography (PET), and multiparametric MRI with computation of rCBV map and K2 map. Three nuclear physicians and three radiologists with different levels of experience delineated the 18-F-FET-PET/CT and 6 MRI sequences, respectively. Spatial similarity (Dice and Jaccard: DSC and JSC) and overlap (Overlap: OV) coefficients were calculated between the readers for each sequence. Results: DSC, JSC, and OV were high for 18F-FET PET/CT, T1-GD, and T2-FLAIR (>0.67). The Spearman correlation coefficient between readers was ≥0.6 for these sequences. Cross-comparison of similarity and overlap parameters showed significant differences for DSC and JSC between 18F-FET PET/CT and T2-FLAIR and for JSC between 18F-FET PET/CT and T1-GD with higher values for 18F-FET PET/CT. No significant difference was found between T1-GD and T2-FLAIR. rCBV, K2, b1000, and ADC showed correlation coefficients between readers <0.6. Conclusion: The interobserver agreements for tumor volume delineations were high for 18-F-FET-PET/CT, T1-GD, and T2-FLAIR. The DWI (b1000, ADC), rCBV, and K2-based sequences, as performed, did not seem sufficiently reproducible to be used in daily practice.

Four-dimensional computed tomography angiography analysis of internal carotid arteries opacification at the skull base to detect delayed cerebral ischemia: a feasibility study.

PURPOSE: Delayed cerebral ischemia represents a significant cause of poor functional outcome for patients with vasospasm after subarachnoid hemorrhage. We investigated whether delayed cerebral ischemia could be detected by the arterial opacification of internal carotid artery at the level of the skull base. METHODS: In this exploratory, nested retrospective cohort diagnostic accuracy study, patients with clinical and/or transcranial Doppler suspicion of vasospasm who underwent four-dimensional computed tomography angiography were included. They were split into two groups for the main endpoint analysis, according to the actually adopted morphological (cerebral infarction) and clinical criteria (neurologic deterioration) of delayed cerebral ischemia. Opacification with a temporal resolution of 0.15 s of both internal carotid arteries at the skull base level was obtained through a semi-automated segmentation method based on skeletonization, and analyzed by a wavelet transform (rbio2.2, level 1). The results obtained by k-means clustering were analyzed with regard to the state of delayed cerebral infarction. RESULTS: Over ten patients included and analyzed, five patients presented a delayed cerebral ischemia, two of them in both side. The semi-automated processing and analysis clustered two different types of opacification curves. The obtaining of a nonlinear opacification pattern was associated (p < 0.001) with delayed cerebral ischemia. CONCLUSIONS: The analysis of arterial opacification of internal carotid arteries at skull base by the proposed processing is feasible and leads to cluster two types of opacification that may help to early detect and prevent delayed cerebral ischemia, in particularly when examinations are artifacted by aneurysm treatment materials.

Radiotherapy target volume definition in newly diagnosed high grade glioma using 18F-FET PET imaging and multiparametric perfusion MRI: A prospective study (IMAGG).

PURPOSE: The aim of this study was to prospectively investigate tumor volume delineation by amino acid PET and multiparametric perfusion magnetic resonance imaging (MRI) in patients with newly diagnosed, untreated high grade glioma (HGG). MATERIALS AND METHODS: Thirty patients with histologically confirmed HGG underwent O-(2-[18F]-fluoroethyl)-l-tyrosine (18F-FET) positron emission tomography (PET), conventional Magnetic Resonance Imaging (MRI) as contrast-enhanced (CE) and fluid-attenuated inversion recovery (FLAIR) and multiparametric MRI as relative cerebral blood volume (rCBV) and permeability estimation map (K2). Areas of MRI volumes were semi-automatically segmented. The percentage overlap volumes, Dice and Jaccard spatial similarity coefficients (OV, DSC, JSC) were calculated. RESULTS: The 18F-FET tumor volume was significantly larger than the CE volume (median 43.5 mL (2.5-124.9) vs. 23.8 mL (1.4-80.3), p = 0.005). The OV between 18F-FET uptake and CE volume was low (median OV 0.59 (0.10-1)), as well as spatial similarity (median DSC 0.52 (0.07-0.78); median JSC 0.35 (0.03-0.64)). Twenty-five patients demonstrated both rCBV and CE on MRI: The median rCBV tumor volume was significantly smaller than the median CE volume (p < 0.001). The OV was high (median 0.83 (0.54-1)), but the spatial similarity was low (median DSC 0.45 (0.04-0.83); median JSC 0.29 (0.07-0.71)). Twenty-eight patients demonstrated both K2 and CE on MRI. The median K2 tumor volume was not significantly larger than the median CE volume. The OV was high (median OV 0.90 (0.61-1)), and the spatial similarity was moderate (median DSC 0.75 (0.01-0.83); median JSC 0.60 (0.11-0.89)). CONCLUSION: We demonstrated that multiparametric perfusion MRI volumes (rCBV, K2) were highly correlated with CE T1 gadolinium volumes whereas 18F-FET PET provided complementary information, suggesting that the metabolically active tumor volume in patients with newly diagnosed untreated HGG is critically underestimated by contrast enhanced MRI. 18F-FET PET imaging may help to improve target volume delineation accuracy for radiotherapy planning.

Consensus Guidelines of the French Society of Neuroradiology (SFNR) on the use of Gadolinium-Based Contrast agents (GBCAs) and related MRI protocols in Neuroradiology.

Gadolinium-based contrast agents (GBCAs) are used in up to 35% of magnetic resonance imaging (MRI) examinations and are associated with an excellent safety profile. Nevertheless, two main issues have arisen in the last two decades: the risk of nephrogenic systemic fibrosis and the risk of gadolinium deposition and retention. As a first step, this article reviews the different categories of GBCAs available in neuroradiology, their issues, and provides updates regarding the use of these agents in routine daily practice. Recent advances in MRI technology, as well as the development of new MRI sequences, have made GBCA injection avoidable in many indications, especially in patients with chronic diseases when iterative MRIs are required and when essential diagnostic information can be obtained without contrast enhancement. These recent advances also lead to changes in recommended MRI protocols. Thus, in a second step, this review focuses on consensus concerning brain MRI protocols in 10 common situations (acute ischemic stroke, intracerebral hemorrhage, cerebral venous thrombosis, multiple sclerosis, chronic headache, intracranial infection, intra- and extra-axial brain tumors, vestibular schwannoma and pituitary adenoma). The latter allowing the standardization of practices in neuroradiology. Recommendations were also made concerning the use of GBCAs in neuroradiology, based on evidence in the literature and/or by consensus between the different coauthors.

A Collet-Sicard syndrome due to internal carotid artery dissection associated with cerebral amyloid angiopathy-related inflammation.

BACKGROUND: Cerebral amyloid angiopathy-related inflammation is a rare condition with approximately 100 reported cases. Its clinical manifestations are varied. We report here a novel presentation of this disease. CASE PRESENTATION: A 61-year-old Caucasian man presented with rapidly progressive paralysis of the IX, X, XI and XII right cranial nerves associated with right central facial nerve palsy. Brain computed tomography angiography and cerebral catheter angiography found a focal fusiform enlargement of the distal cervical portion of the right internal carotid artery, related to a pseudo-aneurysm suggesting an evolution of a dissection and intra-cranial vessel dysplasia. Brain magnetic resonance imaging showed multiple asymmetrical subcortical regions of hyperintensity on T2 fluid-attenuated inversion recovery sequences. Punctiform cortical hyposignals on T2-weighted gradient echo magnetic resonance imaging sequences were mostly congruent with the white matter hyperintensities. There was a decreased cerebral perfusion at the frontal hyperintense fluid-attenuated inversion recovery region. Spectrometry identified a lactate-lipid peak. A brain biopsy showed intravascular amyloid deposits. Corticosteroid therapy was initiated, leading to a dramatic improvement of both clinical condition and magnetic resonance imaging brain lesions. CONCLUSION: This case report suggests that extra-cranial vasculitis and dysplasia can exceptionally be found in patients satisfying cerebral amyloid angiopathy-related inflammation criteria.

Imaging and identification of brown adipose tissue on CT scan.

Two types of adipose tissue (AT) have been described in the field of physiology: white (W) and brown (B) AT. Although WAT is well identified on human imaging, BAT imaging aspect remains to be further explored. The aim of this study was to investigate imaging aspect of BAT and its identification on CT (computed tomography) with iodine-based contrast media injection. We retrospectively reviewed 464 positron emission tomography (PET)/CT, performed during 21 months on adults younger than 37 years. In 39 cases only, the PET revealed the presence of activated BAT. ROI was placed on both white and brown adipose tissue simultaneously on both PET and CT. Several patients' characteristics (blood sugar level, gender, age, body mass index) as well as BAT and WAT parameters were assessed. Mean CT densities for WAT and BAT were -99·5 HU versus -32·6, mean SUV were 1·38 versus 13·2 and SUVmax were 1·79 versus 16·57, respectively. We found a statistically significant inverse relation between BMI and BAT density. BAT has a higher density than WAT. In this manner, BAT can be misinterpreted as an infiltration of adipose tissue in neoplasic and inflammatory context. Contrast-enhanced CT scan allows visualization and identification of BAT.

Oculomotor Nerve Palsy Complicates Third Ventricle Colloid Cyst Endoscopic Removal: Case Report.

BACKGROUND: A colloid cyst is a rare benign tumor. If indicated, surgical treatment can be realized using a microsurgical technique or an endoscopic technique. We report an uncommon complication of a third ventricle colloid cyst endoscopic removal. CASE DESCRIPTION: The cyst was incidentally discovered on computed tomography scan workup for mild head trauma in a 20-year-old male. Minor headache and minor memory loss were noted on clinical examination. Magnetic resonance imaging workup revealed obstructive hydrocephaly of the lateral ventricles associated with left uncal herniation. Surgery was uneventful. However, left oculomotor palsy was noted postoperatively. Workup revealed oculomotor nerve injury and isolated left mammillary body ischemia, secondary to worsened uncal herniation. This worsening might be caused by acute left ventricle hydrocephaly ascribed to interventricular foramen obstruction during cyst removal. CONCLUSION: Therefore, in similar presentation, realizing septum fenestration before cyst removal should relieve the pressure in the lateral ventricles thus decreasing the risk of herniation.

Bone marrow fat quantification of osteoporotic vertebral compression fractures: comparison of multi-voxel proton MR spectroscopy and chemical-shift gradient-echo MR imaging.

BACKGROUND: Only a few studies have used in/opposed phase method for a quantitative evaluation of fat fraction in the spine. PURPOSE: To compare multivoxel proton MR spectroscopy and chemical-shift gradient-echo MR imaging for bone marrow fat quantification in vertebral compression fractures (VCF). MATERIAL AND METHODS: Vertebral marrow fat quantification in fifteen patients was measured at 3.0-T. Multi-voxel proton spectroscopy (MRS) and in/opposed-phase MR imaging using a fat map build with a triple-echo gradient-echo sequence was used. All the patients had benign vertebral collapse. Bone marrow fat content was evaluated by both techniques in compressed (acute or chronic) and in non-compressed vertebrae. RESULTS: The percentage of fat fraction measured by the triple-echo sequence was well correlated with those calculated by MRS (r(2) = 0.85; P < 10(-4)). There was a significant decrease of fat fraction in acute VCF versus both chronic VCF (P < 10(-9)) and non-fractured vertebrae (P < 10(-7)). There was no significant difference in fat fraction evaluated by both techniques between non-fractured vertebrae and chronic VCF. CONCLUSION: We have validated the in/opposed phase method compared with MRS for vertebral bone marrow fat quantification. The fat mapping using a triple-echo gradient-echo sequence allows distinguishing acute and chronic benign VCF.

Tumor volume and metabolism of prostate cancer determined by proton magnetic resonance spectroscopic imaging at 3T without endorectal coil reveal potential clinical implications in the context of radiation oncology.

PURPOSE: To determine whether a relationship exists between the tumor volume (TV) or relative choline content determined using magnetic resonance spectroscopy imaging (MRSI) at 3T and the clinical prognostic parameters for patients with localized prostate cancer (PCa). METHODS AND MATERIALS: A total of 72 men (mean age, 67.8 ± 6.2 years) were stratified as having low-risk (n = 26), intermediate-risk (n = 24), or high-risk (n = 22) PCa. MRSI was performed at 3T using a phased-array coil. Spectra are expressed as the total choline/citrate, total choline plus creatine/citrate, and total choline plus polyamines plus creatine/citrate ratios. The mean ratio of the most pathologic voxels and the MRSI-based TV were also determined. RESULTS: The mean values of the total choline/citrate, total choline plus creatine/citrate, and total choline plus polyamine plus creatine/citrate ratios were greater for Stage T2b or greater tumors vs. Stage T2a or less tumors: 7.53 ± 13.60 vs. 2.31 ± 5.65 (p = .018), 8.98 ± 14.58 vs. 2.56 ± 5.70 (p = .016), and 10.32 ± 15.47 vs. 3.55 ± 6.16 (p = .014), respectively. The mean MRSI-based TV for Stage T2b or greater and Stage T2a or less tumors was significantly different (2.23 ± 2.62 cm(3) vs. 1.26 ± 2.06 cm(3), respectively; p = .030). This TV correlated with increased prostate-specific antigen levels (odds ratio, 1.293; p = .012). Patients with high-risk PCa had a larger TV than did the patients with intermediate-risk PCa. A similar result was found for the intermediate-risk group compared with the low-risk group (odds ratio, 1.225; p = .041). CONCLUSION: Biomarkers expressing the relative choline content and TV were significant parameters for the localization of PCa and could be helpful for determining the prognosis more accurately.

Multiple cerebral and spinal cord cavernomas in Klippel-Trenaunay-Weber syndrome.

Klippel-Trenaunay-Weber syndrome (KTWS) is a rare syndrome in which patients harbor cutaneous hemangiomas, venous varicosities, and osseous-soft tissue hypertrophy of the affected limb. The clinical presentation of this syndrome is variable and the etiopathogenesis is presumably genetic in view of recent discoveries of RASA1 gene mutations in KTWS patients. Similarly, the KRIT1 gene is involved in pathogenesis of cavernous angiomas. Both RASA1 and KRIT1 genes interact with Rap1a protein, a member of the Ras family of guanosine triphosphatases (GTPases) signalling cellular adhesion. We report a 55-year-old male with KTWS harboring multiple cavernous angiomas in the thoracic spinal cord and the brainstem, as revealed by MRI. Angiography ruled out arteriovenous malformation. The patient was managed conservatively. The rarity of cavernous angiomas in KTWS and the possibilities of shared genetic pathways between KTWS and cavernous angiomas are discussed.

Multiple cysts of the corpus callosum and psychomotor delay in a patient with a 3.1 Mb 15q24.1q24.2 interstitial deletion identified by array-CGH.

We describe a 46-month-old child presenting with developmental delay, mild facial dysmorphism, micropenis, strabismus and striking multiple cysts of the corpus callosum who was found to have a de novo interstitial 3.1 Mb 15q24.1q24.2 microdeletion using a 244 K microarray-based comparative genomic hybridization (array-CGH). The cystic lesions were located in the anterior half of the corpus callosum and did not take up gadolinium contrast. There was no other brain abnormality, and the gyral pattern and myelination were normal. There was no history of infectious disease or vascular injury and a metabolic disease was ruled out. Such cystic lesions of the corpus callosum are exceptional in the pediatric literature. Although these brain abnormalities have not been described in other reports with 15q24 microdeletion, we believe that they might be related to the cytogenetic abnormality since the work-up for other causes was negative. We suggest that a chromosomal rearrangement should be ruled out when such corpus callosum lesions are identified.

Nasopharyngeal cysts.

INTRODUCTION: Nasopharyngeal cysts are uncommon, and are mostly asymptomatic. However, these lesions are infrequently found during routine endoscopies and imaging studies. In even more rare cases, they may be the source for unexplained sinonasal symptoms, such as CSF rhinorrhea, visual disturbances and nasal obstruction. PURPOSE OF REVIEW: This presentation systematically reviews the different nasopharyngeal cysts encountered in children, emphasizing the current knowledge on pathophysiology, recent advances in molecular biology and prenatal diagnosis, clinical presentation, imaging and treatment options. SUMMARY: With the advent of flexible and rigid fiber-optic technology and modern imaging techniques, and in particularly prenatal diagnostic techniques, nasopharyngeal cysts recognition is more common than previous times and requires an appropriate consideration. Familiarity with these lesions is essential for the pediatric otolaryngologist.

Combined SPIO-gadolinium magnetic resonance imaging in cirrhotic patients: negative predictive value and role in screening for hepatocellular carcinoma.

BACKGROUND: The objective of our study was to assess the negative predictive value (NPV) of double-contrast MRI (DC-MRI) with SPIO and gadolinium, and to determine the role of DC-MRI in screening for hepatocellular carcinoma (HCC) in cirrhotic patients. METHODS: We retrospectively included 160 DC-MRI scans done as second-line investigations in 119 patients with cirrhosis over a 25-month period. Two radiologists independently classified the MRI scans as strongly suggesting HCC (HCC Group), showing benign nodules (benign nodules Group), showing no nodules (no-nodules Group) or indeterminate; they assigned a diagnostic confidence score (DCS) using a 0-10 scale. The reference standard was histology or results of follow-up investigations. Mean follow-up was 16.9 months (12-28 months). RESULTS: The radiologists disagreed for two scans (kappa = 0.98). Of 112 scans [benign nodules Group (n = 32) and no-nodules Group (n = 80)], 11 were excluded (3 patients lost to follow-up and 8 who died with no known cancer) while a HCC was detected during follow-up in 8 patients, yielding a NPV of 92% (93/101) (95% confidence interval, 85%-97%). The DCS was in the 4-6 range (indicating uncertainty) for only 6 (3.75%) scans. CONCLUSIONS: DC-MRI is reliable and reproducible. Its high NPV suggests a role as a second-line investigation after ultrasonography, for HCC screening.

Imaging of nasopharyngeal cysts and bursae.

Cysts and bursae of the nasopharynx are uncommon and seldom symptomatic when compared with malignant tumors of this region. However, it is noteworthy that in the presence of symptoms, a good knowledge of their radiological appearance is useful to establish the correct diagnosis. Cysts of Rathke's pouch, pharyngeal bursa of Luschka, Tornwaldt's cysts, retentional cysts of the seromucinous glands, oncocytic cysts, intra-adenoid cysts, branchial cysts, prevertebral or retropharyngeal abscess and pseudocysts of the nasopharynx will be discussed in this paper.

Chronic mesenteric ischemia: imaging and percutaneous treatment.

Chronic mesenteric ischemia (CMI) is rare and is often diagnosed late. Fatal malabsorption-related complications or acute ischemic events occur in the absence of treatment. Diagnosis depends on careful acquisition of a medical history and elimination of other conditions. No sensitive and specific tests are available for functional diagnosis of CMI. If other causes of abdominal pain and weight loss have been confidently ruled out, evidence of visceral artery occlusion at noninvasive imaging (Doppler ultrasonography, computed tomographic angiography, and magnetic resonance angiography) suggests CMI. Until the 1990s, open surgery was considered the treatment of choice; percutaneous transluminal angioplasty (PTA) was reserved for patients for whom surgery carried a high risk. However, open surgery carries a nonnegligible risk of morbidity and mortality. In recent years, PTA with stent placement has been recognized as a minimally invasive means of obtaining good long-term results with an acceptable recurrence rate and consequently has been suggested for primary treatment of CMI. New treatments including administration of fibrinolytic agents before PTA of chronic occlusions, routine revascularization of one or more arteries, and stent placement will probably be validated in the near future. Similarly, new data on selection of the best approach will become available soon.