Monica S. Pearl

Practical techniques for reducing radiation exposure during cerebral angiography procedures

Purpose DSA remains the gold standard imaging method for the evaluation of many cerebrovascular disorders, in particular cerebral aneurysms and vascular malformations. The purpose of this study was to demonstrate the effect of modifying DSA frame rate, fluoroscopic and roadmap pulse rates, and flat panel detector (FPD) position on the radiation dose delivered during routine views for a cerebral angiogram in a phantom model. Materials and methods Adult skull and abdomen/pelvis anthropomorphic phantoms were used to compare the radiation dose metrics Ka,r (in mGy), PKA (in μGym2), and fluoroscopy time (in minutes) after modification of fluoroscopic pulses per second (p/s), DSA frames per second (f/s), and FPD position and collimation in three components of a cerebral angiogram: (1) femoral artery access, (2) roadmap guidance, and (3) biplane cerebral DSA. Results For femoral artery access, DSA protocols resulted in significantly higher doses than those utilizing fluoroscopy alone (p=0.007). Roadmaps using 3 p/s or 4 p/s delivered significantly less dose than higher pulse rates (p=0.008). The ranges of delivered doses for biplane cerebral DSA were 347.3–1188.5 mGy and 3914.54–9518.78 μGym2. The lowest radiation doses were generated by the variable frame rate DSA protocols. Conclusions Replacing femoral arterial access evaluations by DSA with fluoroscopy, utilizing lower pulse rates during fluoroscopy and roadmap guidance, and choosing variable frame rates for DSA are simple techniques that may be considered by operators in their clinical practices to lower radiation dose during cerebral angiography procedures.

High-Resolution Secondary Reconstructions with the Use of Flat Panel CT in the Clinical Assessment of Patients with Cochlear Implants

SUMMARY: Radiologic assessment of cochlear implants can be limited because of metallic streak artifacts and the high attenuation of the temporal bones. We report on 14 patients with 18 cochlear implants (17 Med-El standard 31.5-mm arrays, 1 Med-El medium 24-mm array) who underwent flat panel CT with the use of high-resolution secondary reconstruction techniques. Flat panel CT depicted the insertion site, cochlear implant course, and all 216 individual electrode contacts. The calculated mean angular insertion depth for standard arrays was 591.9° (SD = 70.9; range, 280°). High-resolution secondary reconstructions of the initial flat panel CT dataset, by use of a manually generated field of view, Hounsfield unit kernel type, and sharp image characteristics, provided high-quality images with improved spatial resolution. Flat panel CT is a promising imaging tool for the postoperative evaluation of cochlear implant placement.

Cerebral Venous Development in Relation to Developmental Venous Anomalies and Vein of Galen Aneurysmal Malformations

Cerebrovascular venous development and intracranial vascular malformations are extensive topics for which volumes of text may be devoted. However, a basic knowledge of the embryology of cerebral venous system and venous architecture is essential for understanding of cerebral vascular malformations. The aim of this work is to provide the reader with a brief overview of the development of the cranial venous anatomy. We will highlight the superficial and deep venous systems with special attention to developmental venous anomalies and vein of Galen aneurysmal malformations.

Real-time MRI for precise and predictable intra-arterial stem cell delivery to the central nervous system

Stem cell therapy for neurological disorders reached a pivotal point when the efficacy of several cell types was demonstrated in small animal models. Translation of stem cell therapy is contingent upon overcoming the challenge of effective cell delivery to the human brain, which has a volume ∼1000 times larger than that of the mouse. Intra-arterial injection can achieve a broad, global, but also on-demand spatially targeted biodistribution; however, its utility has been limited by unpredictable cell destination and homing as dictated by the vascular territory, as well as by safety concerns. We show here that high-speed MRI can be used to visualize the intravascular distribution of a superparamagnetic iron oxide contrast agent and can thus be used to accurately predict the distribution of intra-arterial administered stem cells. Moreover, high-speed MRI enables the real-time visualization of cell homing, providing the opportunity for immediate intervention in the case of undesired biodistribution.

Salicylic acid analogues as chemical exchange saturation transfer MRI contrast agents for the assessment of brain perfusion territory and blood-brain barrier opening after intra-arterial infusion

The blood–brain barrier (BBB) is a major obstacle for drug delivery to the brain. Predicted, focal opening of the BBB through intra-arterial infusion of hyperosmolar mannitol is feasible, but there is a need to facilitate imaging techniques (e.g. MRI) to guide interventional procedures and assess the outcomes. Here, we show that salicylic acid analogues (SAA) can depict the brain territory supplied by the catheter and detect the BBB opening, through chemical exchange saturation transfer (CEST) MRI. Hyperosmolar SAA solutions themselves are also capable of opening the BBB, and, when multiple SAA agents were co-injected, their locoregional perfusion could be differentiated.

Deeper Cochlear Implant Electrode Insertion Angle Improves Detection of Musical Sound Quality Deterioration Related to Bass Frequency Removal.

Background: Cochlear implant (CI) electrode arrays typically do not reach the most apical regions of the cochlea that intrinsically encode low frequencies. This may contribute to diminished implant-mediated musical sound quality perception. The objective of this study was to assess the effect of varying degrees of apical cochlear stimulation (measured by angular insertion depth) on musical sound quality discrimination. Hypothesis: Increased apical cochlear stimulation will improve low-frequency perception and musical sound quality discrimination. Methods: Standard (31.5 mm, n = 17) and medium (24 mm, n = 8) array Med-EL CI users, and normal hearing (NH) listeners (n = 16) participated. Imaging confirmed angular insertion depth. Participants completed a musical discrimination task in which they listened to a real-world musical stimulus (labeled reference) and provided sound quality ratings to versions of the reference, which included a hidden reference and test stimuli with increasing amounts of low-frequency removal. Scores for each CI users were calculated on the basis of how much their ratings differed from NH listeners for each stimulus version. Results: Medium array and standard users had significantly different insertion depths (389.4±64.5 and 583.9 ± 78.5 degrees, respectively; p < 0.001). A significant Pearsons correlation was observed between angular insertion depth and the hidden reference scores (p < 0.05). Conclusion: CI users with greater apical stimulation made sound quality discriminations that more closely resembled those of NH controls for stimuli that contained low frequencies (<200 Hz of information). These findings suggest that increased apical cochlear stimulation improves musical low-frequency perception, which may provide a more satisfactory music listening experience for CI users.

Analysis of radiation doses incurred during diagnostic cerebral angiography after the implementation of dose reduction strategies

Background One goal of increasing awareness of radiation dose is to encourage personal and technical modifications in order to reduce the radiation exposure of patients and staff. Objective To analyze the radiation doses incurred during diagnostic cerebral angiography and the angiographic techniques practiced over a 4-year period, in order to demonstrate the effectiveness of implementing radiation dose reduction strategies. Methods A retrospective review of the first 50 consecutive adult and pediatric patients undergoing diagnostic cerebral angiography each year from 2010 to 2013 was performed. Angiograms and procedure examination protocols were reviewed for patient age, gender, diagnosis, angiography techniques, fluoroscopy time, reference point air kerma (Ka,r in mGy), and kerma-area product (PKA in μGym2). Results From January 2010 to June 2013, a total of 231 diagnostic cerebral angiograms were reviewed (200 adults, 31 children). Adult patients were aged from 19 to 94 years and included 77 men and 123 women. Pediatric patients were aged from 2 to 18 years and comprised 11 boys and 20 girls. Median Ka,r and PKA significantly decreased from 2010 to 2013 in adults (1867 mGy; 21 231 µGym2 vs 653 mGy; 7860 µGym2) and children (644 mGy; 6495 µGym2 vs138 mGy; 1465 µGym2), (p<0.001). Conclusions Increased awareness and implementation of dose reduction strategies resulted in decreased radiation doses for diagnostic cerebral angiography both in adult and pediatric patients. The use of lower and variable digital subtraction angiography frame rates and tailored examinations contributed significantly to the reduced radiation doses observed during diagnostic cerebral angiography.

Flat-Panel CT Imaging for Individualized Pitch Mapping in Cochlear Implant Users.

Objective: This study aims to identify electrode contact location and to assess frequency deviation between predicted and actual frequency allocation maps in cochlear implant (CI) users. Study Design and Methods: This is a retrospective clinical study. Flat-panel computed tomography (FPCT) scans were collected for 17 CI users. Cochlear length was measured using three-dimensional curved multiplanar reconstruction on high-resolution secondary reconstructions. Each electrodes percentage of distance from the base of the helicotrema was measured, and a modified Greenwoods function was applied. The patients’ frequency allocation maps were retrieved from electronic medical records and compared with their calculated characteristic frequencies. Results: Our results revealed that reprogramming based on FPCT imaging findings might improve 83% (n = 216) of 260 electrode contacts. The most basal and apical electrodes (12, 11, 10, 5, 4, 3, 2, and 1) most consistently deviated (>83% of the time) from their theoretical characteristic frequencies; the basal electrodes undershot and the apical electrodes overshot their theoretical values. Frequency mismatch between the characteristic frequencies of auditory neurons and programmed center frequencies ranges from 0.41 to 1.51 in octave bands. Conclusions: Using FPCT imaging and a modified Greenwoods function, we identify a mathematical discrepancy between theoretical and actual CI placement with respect to frequency–place mapping. We demonstrate a clinically reproducible and direct assessment of frequency–place mismatch. Our individualized calculations account for inter-individual variability in cochlear lengths, operative differences in insertion depths, and electrode array kinking within the cochlea. The benefits of allocating electrode contact frequencies to their tonotopy-derived locations in the cochlea were not investigated in this study, and future prospective trials are needed to demonstrate the consequences of personalized pitch mapping for CI users with respect to speech and pitch perception.

Neuroimaging findings in children with Keutel syndrome

BackgroundKeutel syndrome is a rare autosomal-recessive condition characterized by abnormal cartilage calcification. Neuroimaging findings associated with this condition have been randomly described in the literature.ObjectiveTo systematically evaluate the neuroimaging findings in a series of children with Keutel syndrome to broaden our base of knowledge.Materials and methodsFour children with confirmed Keutel syndrome were reviewed for the brain, head and neck imaging findings.ResultsThree of the four children, all siblings, showed evidence of moyamoya syndrome. All four siblings had pinna cartilage calcification.ConclusionWe propose that Keutel syndrome be considered and included among the secondary causes of moyamoya syndrome. In children with petrified auricle and neurological symptoms, Keutel syndrome should be considered and brain MRI with MRA is required.

Diagnostic quality and accuracy of low dose 3D-DSA protocols in the evaluation of intracranial aneurysms

Background 3D-DSA is the ‘gold standard’ imaging technique for the diagnosis and characterization of intracranial aneurysms. Objective To compare the image quality and accuracy of low dose 3D-DSA protocols in patients with unruptured intracranial aneurysms. Materials and methods The standard manufacturer 5 s 0.36 μGy/f protocol and one of three low dose 3D-DSA protocols (5 s 0.10 μGy/f, 5 s 0.17 μGy/f, 5 s 0.24 μGy/f) were performed in 12 patients with unruptured intracranial aneurysms. Three interventional neuroradiologists, two neurosurgeons, and two neurologists rated the image quality of all 3D reconstructions as good, acceptable, or poor. Three interventional neuroradiologists measured two dimensions of each aneurysm for all protocols. The radiation dose metric Ka,r (reference point air kerma, in mGy) was recorded for each 3D-DSA protocol. Results The standard 5 s 0.36 μGy/f protocol earned the highest average subjective rating of 2.76, followed by the 5 s 0.24 μGy/f (2.72), and 5 s 0.17 μGy/f (2.59) protocols. The ranges of differences in aneurysm measurements between the 5 s 0.24 μGy/f protocol and the standard were <0.5 mm. The median Ka,r metrics for each protocol were as follows: 5 s 0.36 μGy/f (89.0 mGy), 5 s 0.24 μGy/f (57.7 mGy), 5 s 0.17 μGy/f (45.9 mGy), and 5 s 0.10 μGy/f (27.6 mGy). Conclusions Low dose 3D-DSA protocols with preserved image quality are achievable, and can help reduce exposure of patients and operators to unnecessary radiation. The 5 s 0.24 μGy/f protocol generates one-third smaller radiation dose than the standard 5 s 0.36 μGy/f protocol without compromising diagnostic image quality or accuracy.