Aditya Bharatha

Statistical validation of image segmentation quality based on a spatial overlap index.

RATIONALE AND OBJECTIVES To examine a statistical validation method based on the spatial overlap between two sets of segmentations of the same anatomy. MATERIALS AND METHODS The Dice similarity coefficient (DSC) was used as a statistical validation metric to evaluate the performance of both the reproducibility of manual segmentations and the spatial overlap accuracy of automated probabilistic fractional segmentation of MR images, illustrated on two clinical examples. Example 1: 10 consecutive cases of prostate brachytherapy patients underwent both preoperative 1.5T and intraoperative 0.5T MR imaging. For each case, 5 repeated manual segmentations of the prostate peripheral zone were performed separately on preoperative and on intraoperative images. Example 2: A semi-automated probabilistic fractional segmentation algorithm was applied to MR imaging of 9 cases with 3 types of brain tumors. DSC values were computed and logit-transformed values were compared in the mean with the analysis of variance (ANOVA). RESULTS Example 1: The mean DSCs of 0.883 (range, 0.876-0.893) with 1.5T preoperative MRI and 0.838 (range, 0.819-0.852) with 0.5T intraoperative MRI (P < .001) were within and at the margin of the range of good reproducibility, respectively. Example 2: Wide ranges of DSC were observed in brain tumor segmentations: Meningiomas (0.519-0.893), astrocytomas (0.487-0.972), and other mixed gliomas (0.490-0.899). CONCLUSION The DSC value is a simple and useful summary measure of spatial overlap, which can be applied to studies of reproducibility and accuracy in image segmentation. We observed generally satisfactory but variable validation results in two clinical applications. This metric may be adapted for similar validation tasks.

Evaluation of three‐dimensional finite element‐based deformable registration of pre‐ and intraoperative prostate imaging

In this report we evaluate an image registration technique that can improve the information content of intraoperative image data by deformable matching of preoperative images. In this study, pretreatment 1.5 tesla (T) magnetic resonance (MR) images of the prostate are registered with 0.5 T intraoperative images. The method involves rigid and nonrigid registration using biomechanical finite element modeling. Preoperative 1.5 T MR imaging is conducted with the patient supine, using an endorectal coil, while intraoperatively, the patient is in the lithotomy position with a rectal obturator in place. We have previously observed that these changes in patient position and rectal filling produce a shape change in the prostate. The registration of 1.5 T preoperative images depicting the prostate substructure [namely central gland (CG) and peripheral zone (PZ)] to 0.5 T intraoperative MR images using this method can facilitate the segmentation of the substructure of the gland for radiation treatment planning. After creating and validating a dataset of manually segmented glands from images obtained in ten sequential MR-guided brachytherapy cases, we conducted a set of experiments to assess our hypothesis that the proposed registration system can significantly improve the quality of matching of the total gland (TG), CG, and PZ. The results showed that the method statistically-significantly improves the quality of match (compared to rigid registration), raising the Dice similarity coefficient (DSC) from prematched coefficients of 0.81, 0.78, and 0.59 for TG, CG, and PZ, respectively, to 0.94, 0.86, and 0.76. A point-based measure of registration agreement was also improved by the deformable registration. CG and PZ volumes are not changed by the registration, indicating that the method maintains the biomechanical topology of the prostate. Although this strategy was tested for MRI-guided brachytherapy, the preliminary results from these experiments suggest that it may be applied to other settings such as transrectal ultrasound-guided therapy, where the integration of preoperative MRI may have a significant impact upon treatment planning and guidance.

Association Between MRI Exposure During Pregnancy and Fetal and Childhood Outcomes.

IMPORTANCE Fetal safety of magnetic resonance imaging (MRI) during the first trimester of pregnancy or with gadolinium enhancement at any time of pregnancy is unknown. OBJECTIVE To evaluate the long-term safety after exposure to MRI in the first trimester of pregnancy or to gadolinium at any time during pregnancy. DESIGN, SETTING, AND PARTICIPANTS Universal health care databases in the province of Ontario, Canada, were used to identify all births of more than 20 weeks, from 2003-2015. EXPOSURES Magnetic resonance imaging exposure in the first trimester of pregnancy, or gadolinium MRI exposure at any time in pregnancy. MAIN OUTCOMES AND MEASURES For first-trimester MRI exposure, the risk of stillbirth or neonatal death within 28 days of birth and any congenital anomaly, neoplasm, and hearing or vision loss was evaluated from birth to age 4 years. For gadolinium-enhanced MRI in pregnancy, connective tissue or skin disease resembling nephrogenic systemic fibrosis (NSF-like) and a broader set of rheumatological, inflammatory, or infiltrative skin conditions from birth were identified. RESULTS Of 1 424 105 deliveries (48% girls; mean gestational age, 39 weeks), the overall rate of MRI was 3.97 per 1000 pregnancies. Comparing first-trimester MRI (n = 1737) to no MRI (n = 1 418 451), there were 19 stillbirths or deaths vs 9844 in the unexposed cohort (adjusted relative risk [RR], 1.68; 95% CI, 0.97 to 2.90) for an adjusted risk difference of 4.7 per 1000 person-years (95% CI, -1.6 to 11.0). The risk was also not significantly higher for congenital anomalies, neoplasm, or vision or hearing loss. Comparing gadolinium MRI (n = 397) with no MRI (n = 1 418 451), the hazard ratio for NSF-like outcomes was not statistically significant. The broader outcome of any rheumatological, inflammatory, or infiltrative skin condition occurred in 123 vs 384 180 births (adjusted HR, 1.36; 95% CI, 1.09 to 1.69) for an adjusted risk difference of 45.3 per 1000 person-years (95% CI, 11.3 to 86.8). Stillbirths and neonatal deaths occurred among 7 MRI-exposed vs 9844 unexposed pregnancies (adjusted RR, 3.70; 95% CI, 1.55 to 8.85) for an adjusted risk difference of 47.5 per 1000 pregnancies (95% CI, 9.7 to 138.2). CONCLUSIONS AND RELEVANCE Exposure to MRI during the first trimester of pregnancy compared with nonexposure was not associated with increased risk of harm to the fetus or in early childhood. Gadolinium MRI at any time during pregnancy was associated with an increased risk of a broad set of rheumatological, inflammatory, or infiltrative skin conditions and for stillbirth or neonatal death. The study may not have been able to detect rare adverse outcomes.

Quantitative MR Imaging Assessment of Prostate Gland Deformation before and During MR Imaging–Guided Brachytherapy

RATIONALE AND OBJECTIVES The authors performed this study to document the deformations that occur between pretreatment magnetic resonance (MR) imaging and intraoperative MR imaging during brachytherapy. MATERIALS AND METHODS MR images obtained at 1.5 and 0.5 T in 10 patients with prostate cancer were analyzed for changes in the shape and substructure of the prostate. Three-dimensional models of the prostate were obtained. The authors measured anteroposterior dimension; total gland, peripheral zone, and central gland volumes; transverse dimension; and superoinferior height. RESULTS Gland deformations were seen at visual inspection of the three-dimensional models. The anteroposterior dimension of the total gland, central gland, and peripheral zone increased from 1.5- to 0.5-T imaging (median dimension, 4.9, 1.5, and 1.8 mm, respectively), and the increase was greatest in the peripheral zone (P < .05, all comparisons). There was a decrease in the transverse dimension from 1.5- to 0.5-T imaging (median, 4.5 mm; P < .005). The total gland volume and the superoinferior height did not show a statistically significant change. CONCLUSION There were significant deformations in the shape of the prostate, especially in the peripheral zone, between the two imaging studies. The likely causes of the shape change are differences in rectal filling (endorectal coil used in 1.5-T studies vs obturator in 0.5-T studies) and/or changes in patient position (supine vs lithotomy). These findings suggest that pretreatment images alone may not be reliable for accurate therapy planning. It may be useful to integrate pre-and intraoperative data.

Intracranial arterial fenestrations: frequency on CT angiography and association with other vascular lesions

Fenestrations (segmental duplications) of the intracranial arteries are rare anomalies, felt to result from incomplete fusion of primitive embryologic vessels. They have been associated with aneurysms and other vascular lesions. The rate of fenestrations based on published angiographic series has been much lower than that at cadaveric series. The purpose of this study is to determine the frequency of fenestrations and associated vascular lesions at CTA. A total of 504 sequential CTA studies from 2005 to 2006 were retrospectively reviewed for the presence of fenestrations, aneurysms and other vascular lesions. Fenestrations were present in 53 patients (11%). Their frequency was not significantly different in patients referred for aneurysm indications, when compared to those referred for non-aneurysm indications. As expected, there was a much higher frequency of aneurysms in the former group. Associated vascular lesions were relatively uncommon. Aneurysms were present at the fenestration site in three patients, and remote from the fenestration site in eight. One fenestration patient with an associated aneurysm at the fenestration site also had an AVM remote from the fenestration. The frequency of fenestrations in this study was higher than in previously published radiologic studies, suggesting that fenestrations are relatively common, and may be more frequently visualized using cross-sectional imaging. Association with aneurysms and other vascular lesions was relatively uncommon. Our results do not support the theory that fenestrations predispose a patient to aneurysms or vascular malformations remote from the site of the fenestration. Although the association of aneurysms at the site of fenestrations is well documented, our results do not show an overall higher rate of aneurysm formation in patients with fenestrations compared to those without.

Brain Arteriovenous Malformation Multiplicity Predicts the Diagnosis of Hereditary Hemorrhagic Telangiectasia Quantitative Assessment

Background and Purpose— The purpose of this study was to quantitatively estimate the relationship between multiplicity of brain arteriovenous malformations (bAVMs) and the diagnosis of hereditary hemorrhagic telangiectasia (HHT). Methods— We combined databases from 2 large North American bAVM referral centers, including demographics, clinical presentation, and angiographic characteristics, and compared patients with HHT with non-HHT patients. Logistic regression analysis was performed to quantify the association between bAVM multiplicity and odds of HHT diagnosis. Sensitivity, specificity, positive and negative predictive value, and positive and negative likelihood ratios were calculated to determine accuracy of bAVM multiplicity for screening HHT. Results— Prevalence of HHT was 2.8% in the combined group. bAVM multiplicity was present in 39% of patients with HHT and was highly associated with diagnosis of HHT in univariate (OR, 83; 95% CI, 40–173; P<0.0001) and multivariable (OR, 86; 95% CI, 38–195; P<0.001) models adjusting for age at presentation (P=0.013), symptomatic presentation (P=0.029), and cohort site (P=0.021). bAVM multiplicity alone was associated with high specificity (99.2%; 95% CI, 98.7%–99.6%) and negative predictive value (98.3%; 95% CI, 97.6%–98.8%) and low sensitivity (39.3%; 95% CI, 26.5%–53.2%) and positive predictive value (59.5%; 95% CI, 42.1%–75.2%). Positive and negative likelihood ratio was 51 and 0.61, respectively, for diagnosis of HHT. HHT bAVMs were also more often smaller in size (<3 cm), noneloquent in location, and associated with superficial venous drainage compared with non-HHT bAVMs. Conclusions— Multiplicity of bAVMs is highly predictive of the diagnosis of HHT. The presence of multiple bAVMs should alert the clinician to the high probability of HHT and lead to comprehensive investigation for this diagnosis.

Brain arteriovenous malformations associated with hereditary hemorrhagic telangiectasia: Gene–phenotype correlations†‡

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant genetic disease with a wide spectrum of vascular malformations (VMs) involving multiple organs. Nine to 16% of patients with HHT harbor brain arteriovenous malformations (AVMs), which can cause intracranial hemorrhage (ICH). Our objective was to study clinical manifestations of brain AVMs in patients with HHT and correlate these with the specific gene mutated. We reviewed records of 171 patients with HHT and brain AVMs. A history of ICH was found in 27% (41/152) patients, with a mean age of 26 ± 18 range, (0–68) years. All of patients with ICH were neurologically asymptomatic prior to ICH. Multiple brain AVMs were found in 23% (170/39) of patients on initial examination. Genetic test results were available in 109 (64%) patients. Mutations in ENG, ACVRL1, and SMAD4 were present in 75 (69%), 18 (17%), and 2 (2%), respectively. A history of ICH was reported in 24% of patients with an ENG mutation and 27% of patients with an ACVRL1 mutation, with a mean age of 26 ± 16 (range, 2–50) and 18 ± 21 (0–48) years, respectively. No statistically significant differences in age at first brain AVM diagnosis, prevalence of ICH history, age at ICH, or other manifestations of brain AVMs were observed among gene groups. In conclusion, no evidence for differences in brain AVM characteristics was observed among HHT gene groups, although we cannot exclude clinically important differences. Larger studies are needed to further guide brain AVM screening decisions in patients with HHT.

Magnetic resonance imaging of facial nerve schwannoma

This study characterizes the magnetic resonance (MR) appearances of facial nerve schwannoma (FNS). We hypothesize that the extent of FNS demonstrated on MR will be greater compared to prior computed tomography studies, that geniculate involvement will be most common, and that cerebellar pontine angle (CPA) and internal auditory canal (IAC) involvement will more frequently result in sensorineural hearing loss (SNHL).

24 – Advanced Nonrigid Registration Algorithms for Image Fusion

This chapter presents an original method to perform nonrigid registration of multimodal images. This iterative algorithm is composed of two steps: the intensity transformation and the geometrical transformation. Two intensity transformation models are proposed, which assume either monofunctional or bifunctional dependence between the intensity values in the images being matched. Both of these models are built using robust estimators to enable precise and accurate transformation solutions. The chapter describes the image registration strategy applied prospectively during several neurosurgical cases. The enhancement provided by intraoperative nonrigid registration to the surgical visualization environment is shown by matching the corticospinal tract of a preoperatively prepared anatomical atlas to the initial and subsequent intraoperative scans of a subject. This matching was carried out prospectively during the neurosurgery, demonstrating the practical value of the approach and its ability to meet the real-time constraints of surgery. The entire image analysis process can be completed in less than 10 min, which has been adequate to display the information to the surgeon.

CT angiographic depiction of a supraclinoid ICA fenestration mimicking aneurysm, confirmed with catheter angiography

Fenestrations (segmental duplications) of the intracranial arteries are rare anomalies that have been associated with aneurysms. Fenestrations of the supraclinoid ICA are extremely rare, with only a few reported cases. We present a supraclinoid ICA fenestration, which on axial CTA images initially mimicked an aneurysm, but was correctly delineated as a fenestration on multiplanar reformatted and 3D reconstructed images. Confirmation was made with conventional angiography. To our knowledge, this represents the first time that this rare variant has been identified with cross-sectional imaging. A review of the literature including proposed embryology is provided.