Comparison of three-dimensional fast spin echo and gradient echo sequences for high-resolution temporal bone imaging

Zero Echo Time vs. T1-Weighted MRI for Assessment of Cortical and Medullary Bone Morphology Abnormalities Using CT as the Reference Standard

BACKGROUND

Conventional MR pulse sequences result in poor signal from low T2 cortical bone because the minimum achievable echo time is limited. A sequence resulting in improved bone contrast is desirable.

PURPOSE

To evaluate the image quality and diagnostic performance of grayscale inversion zero echo time imaging (GI-ZTE) and grayscale inversion T1-weighted imaging (GI-T1WI) compared with computed tomography (CT).

STUDY TYPE

Prospective.

SUBJECTS

A total of 50 patients with musculoskeletal tumors or tumor-like diseases of the lower extremities having MRI and CT studies.

FIELD STRENGTH/SEQUENCE

GI-T1WI and GI-ZTE sequences at 1.5 T.

ASSESSMENT

Assessed cortical and medullary bone morphology abnormalities using CT as the reference standard. Three radiologists scored the images quality and recorded nine metrics to assess the diagnostic performance.

STATISTICAL TESTS

Differences in image quality were calculated using the Wilcoxon signed-rank test. The intraclass correlation coefficient (ICC) was used to analyze the agreement of quantitative lesion parameters between CT and MR sequences, as well as the interobserver reliability. A P value <0.05 was considered statistically significant.

RESULTS

Image quality score was significantly higher for CT images than GI-TIWI images. Except for radiologist 3 [4(0) vs 4 (1)], there was no significant difference in scores between CT and GI-ZTE [radiologist 1: 4 (0) vs 4 (0), P = 0.133; radiologist 2: 4 (0) vs 4 (0), P = 0.085]. There was good-excellent agreement between both MR sequences and CT for size, lesion number, location, sclerotic rim, expanded shell, destruction pattern, and matrix mineralization for all radiologists (ICC: 0.636-1.000). The consistency of periosteal reaction and penetration of the cortex was fair to good (0.481-0.729) between GI-T1WI and CT and good to excellent between GI-ZTE and CT (0.682-0.852).

DATA CONCLUSIONS

GI-ZTE images had superior intermodality agreement with CT images and allowed visualization of more cortical bone detail than GI-T1WI images.

EVIDENCE LEVEL

1.

TECHNICAL EFFICACY

Stage 2.

Cochlear Implantation: Systematic Approach to Preoperative Radiologic Evaluation

Sensorineural hearing loss results from abnormalities that affect the hair cells of the membranous labyrinth, inner ear malformations, and conditions affecting the auditory pathway from the cochlear nerve to the processing centers of the brain. Cochlear implantation is increasingly being performed for hearing rehabilitation owing to expanding indications and a growing number of children and adults with sensorineural hearing loss. An adequate understanding of the temporal bone anatomy and diseases that affect the inner ear is paramount for alerting the operating surgeon about variants and imaging findings that can influence the surgical technique, affect the choice of cochlear implant and electrode type, and help avoid inadvertent complications. In this article, imaging protocols for sensorineural hearing loss and the normal inner ear anatomy are reviewed, with a brief description of cochlear implant devices and surgical techniques. In addition, congenital inner ear malformations and acquired causes of sensorineural hearing loss are discussed, with a focus on imaging findings that may affect surgical planning and outcomes. The anatomic factors and variations that are associated with surgical challenges and may predispose patients to periprocedural complications also are highlighted. ^© RSNA, 2023 Quiz questions for this article are available through the Online Learning Center. Online supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article.

Measuring 3D Cochlear Duct Length on MRI: Is It Accurate and Reliable?

BACKGROUND AND PURPOSE

Prior studies have evaluated cochlear length using CT to select the most suitable cochlear implants and obtain patient-specific anatomy. This study aimed to test the accuracy and reliability of cochlear lateral wall length measurements using 3D MR imaging.

MATERIALS AND METHODS

Two observers measured the cochlear lateral wall length of 35 patients (21 men) with postlingual hearing loss using CT and MR imaging. The intraclass correlation coefficient (with 95% confidence intervals) was used to evaluate intraobserver and interobserver reliability for the 3D cochlear measurements.

RESULTS

The mean age of the participants was 39.85 (SD, 16.60) years. Observer 1 measured the mean lateral wall length as 41.52 (SD, 2.25) mm on CT and 41.44 (SD, 2.18) mm on MR imaging, with a mean difference of 0.08 mm (95% CI, -0.11 to 0.27 mm), while observer 2 measured the mean lateral wall length as 41.74 (SD, 2.69) mm on CT and 42.34 (SD, 2.53) mm on MR imaging, with a mean difference of -0.59 mm (95% CI, -1.00 to -0.20 mm). An intraclass correlation coefficient value of 0.90 (95% CI, 0.84-0.94) for CT and 0.69 (95% CI, 0.46-0.82) for MR imaging was obtained for the interobserver reliability for the full-turn cochlear lateral wall length.

CONCLUSIONS

CT-based 3D cochlear measurements show excellent intraobserver and interobserver reliability, while MR imaging-based lateral wall length measurements have good-to-excellent intraobserver reliability and moderate interobserver reliability. These results corroborate the use of CT for 3D cochlear measurements as a reference method and demonstrate MR imaging to be an alternative acquisition technique with comparably reliable results.

Compressed-sensing accelerated magnetic resonance imaging of inner ear

Objective

To compare conventional method and compressed‐sensing (CS) accelerated 3D balanced fast field echo imaging (bFFE) of inner ear.

Methods

Twenty patients with suspected inner ear disease underwent CS accelerated 3D‐bFFE (CS‐bFFE) and conventional 3D‐bFFE (Con‐bFFE) by a 3T MRI. The overall image quality, motion artifacts, and image quality of specific structures of inner ear were assessed on ordinal scales by three radiologists who were blinded to the scan protocols. Kendall W test was used to evaluate interobserver agreement and Wilcoxon test was performed to compare the image quality and motion artifacts between CS‐bFFE and Con‐bFFE.

Results

The acquisition duration of CS‐bFFE (1 min 53 s) was 49% faster than Con‐bFFE. Three radiologists had good inter‐observer agreement of image quality (Kendall W value of 0.829 for CS‐bFFE and 0.815 for Con‐bFFE) and motion artifacts evaluation (Kendall W value of 0861 for CS‐bFFE and 0.707 for Con‐bFFE). The better overall image quality of CS‐bFFE was assessed (4.93 ± 0.23 for CS‐bFFE, 4.53 ± 0.70 for Con‐bFFE, Z = −2.254, p = 0.024). The image quality score of facial and cochlear nerve gained higher in CS‐bFFE (4.93 ± 0.23 for CS‐bFFE, 4.58 ± 0.64 for Con‐bFFE, Z = −2.094, p = 0.036). No significant difference of motion artifacts (p = 0.050) between CS‐bFFE and Con‐bFFE.

Conclusions

The CS‐bFFE improves image quality and reduces acquisition time significantly, and it is a feasible MRI protocol for inner ear imaging.

MRI of the Internal Auditory Canal, Labyrinth, and Middle Ear: How We Do It

MRI is firmly established as an essential modality in the imaging of the temporal bone and lateral skull base. It is used to evaluate normal anatomic structures, evaluate for vestibular schwannomas, assess for inflammatory and/or infectious processes, and detect residual and/or recurrent cholesteatoma. It is also extensively used in pre- and postoperative evaluations, particularly in patients with vestibular schwannomas and candidates for cochlear implantation. Nevertheless, despite the widespread use of MRI for these purposes, many radiologists remain unfamiliar with the complex anatomy and expected imaging findings with such examinations. The purpose of this review is to provide an overview of the most useful MRI sequences for internal auditory canal and labyrinthine imaging, review the relevant anatomy, and discuss the expected appearances of the most commonly encountered pathologic entities. In addition, the features at pre- and postprocedural MRI will be discussed to help ensure that diagnostic radiologists may be of greatest use to the ordering physicians. © RSNA, 2020.

Diagnostics and therapy of vestibular schwannomas - an interdisciplinary challenge

Vestibular schwannomas (VS) expand slowly in the internal auditory canal, in the cerebellopontine angle, inside the cochlear and the labyrinth. Larger tumors can displace and compress the brainstem. With an annual incidence of 1:100,000 vestibular schwannoma represent 6-7% of all intracranial tumors. In the cerebellopontine angle they are by far the most neoplasm with 90% of all lesions located in this region. Magnetic resonance imaging (MRI), audiometry, and vestibular diagnostics are the mainstays of the clinical workup for patients harboring tumors. The first part of this paper delivers an overview of tumor stages, the most common grading scales for facial nerve function and hearing as well as a short introduction to the examination of vestibular function. Upholding or improving quality of life is the central concern in counseling and treating a patient with vestibular schwannoma. Preservation of neuronal function is essential and the management options - watchful waiting, microsurgery and stereotactic radiation - should be custom-tailored to the individual situation of the patient. Continuing interdisciplinary exchange is important to monitor treatment quality and to improve treatment results. Recently, several articles and reviews have been published on the topic of vestibular schwannoma. On the occasion of the 88^th annual meeting of the German Society of Oto-Rhino-Laryngology, Head and Neck surgery a special volume of the journal "HNO" will be printed. Hence this presentation has been designed to deviate from the traditional standard which commonly consists of a pure literature review. The current paper was conceptually woven around a series of interdisciplinary cases that outline examples for every stage of the disease that show characteristic results for management options to date. Systematic clinical decision pathways have been deduced from our experience and from results reported in the literature. These pathways are graphically outlined after the case presentations. Important criteria for decision making are size and growth rate of the tumor, hearing of the patient and the probability of total tumor resection with preservation of hearing and facial nerve function, age and comorbidity of the patient, best possible control of vertigo and tinnitus and last but not least the patient's preference and choice. In addition to this, the experience and the results of a given center with each treatment modality will figure in the decision making process. We will discuss findings that are reported in the literature regarding facial nerve function, hearing, vertigo, tinnitus, and headache and reflect on recent studies on their influence on the patient's quality of life. Vertigo plays an essential role in this framework since it is an independent predictor of quality of life and a patient's dependence on social welfare. Pathognomonic bilateral vestibular schwannomas that occur in patients suffering from neurofibromatosis typ-2 (NF2) differ from spontaneous unilateral tumors in their biologic behavior. Treatment of neurofibromatosis type-2 patients requires a multidisciplinary team, especially because of the multitude of separate intracranial and spinal lesions. Off-label chemotherapy with Bevacizumab can stabilize tumor size of vestibular schwannomas and even improve hearing over longer periods of time. Hearing rehabilitation in NF2 patients can be achieved with cochlear and auditory brainstem implants.

Depicting the semicircular canals with inner-ear MRI: a comparison of the SPACE and TrueFISP sequences

PURPOSE

To assess the ability of magnetic resonance imaging (MRI) to depict the semicircular canals of the inner ear by comparing results from the sampling perfection with application-optimized contrasts by using different flip angle evolutions (SPACE) sequence with those from the true free induction with steady precession (TrueFISP) sequence.

MATERIALS AND METHODS

A 1.5-T MRI system was used to perform an in vivo study of 10 healthy volunteers and 17 patients. A three-point visual score was employed for assessing the depiction of the semicircular canals and facial and vestibulocochlear nerves and the contrast-to-noise ratio (CNR) was computed for the vestibule and pons on images with the SPACE and TrueFIPS sequences.

RESULTS

There were no susceptibility artifact-related filling defects with the SPACE sequence. However, the TrueFISP sequence showed filling defects for at least one semicircular canal on both sides in seven cases for healthy subjects and in 10 cases for patients. The CNR with the SPACE sequence was significantly higher than with the TrueFISP sequence (P < 0.05). There was no statistically significant difference in depicting the facial and the vestibulocochlear nerves (P = 0.32).

CONCLUSION

For the depiction of the semicircular canal, the SPACE sequence is superior to the TrueFISP sequence.

MR imaging of the internal auditory canal and inner ear at 3T: comparison between 3D driven equilibrium and 3D balanced fast field echo sequences

Objective

To compare the use of 3D driven equilibrium (DRIVE) imaging with 3D balanced fast field echo (bFFE) imaging in the assessment of the anatomic structures of the internal auditory canal (IAC) and inner ear at 3 Tesla (T).

Materials and Methods

Thirty ears of 15 subjects (7 men and 8 women; age range, 22-71 years; average age, 50 years) without evidence of ear problems were examined on a whole-body 3T MR scanner with both 3D DRIVE and 3D bFFE sequences by using an 8-channel sensitivity encoding (SENSE) head coil. Two neuroradiologists reviewed both MR images with particular attention to the visibility of the anatomic structures, including four branches of the cranial nerves within the IAC, anatomic structures of the cochlea, vestibule, and three semicircular canals.

Results

Although both techniques provided images of relatively good quality, the 3D DRIVE sequence was somewhat superior to the 3D bFFE sequence. The discrepancies were more prominent for the basal turn of the cochlea, vestibule, and all semicircular canals, and were thought to be attributed to the presence of greater magnetic susceptibility artifacts inherent to gradient-echo techniques such as bFFE.

Conclusion

Because of higher image quality and less susceptibility artifacts, we highly recommend the employment of 3D DRIVE imaging as the MR imaging choice for the IAC and inner ear.

Fluorine-19 fast recovery fast spin echo imaging for mapping 5-fluorouracil

We investigated the effects of fast recovery (FR) to increase the sensitivity of fluorine-19 ((19)F) fast spin echo (FSE) in mapping 5-fluorouracil (5-FU) and its metabolites. We added an additional 90 degrees pulse (which flips back longitudinal magnetization at the end of the sequence) to the chemical shift selective (19)F FSE pulse sequence. In 5-FU solution, FR remarkably improved the signal-to-noise (S/N) ratio of (19)F 5-FU images, having higher effects with shorter repetition time and smaller echo train numbers. In animal studies, FR produced a conspicuous increase in (19)F signals in the urinary bladder. FR effects for (19)F signals in the liver were smaller than those in other organs but still substantial. Utilization of FR in (19)F FSE images promises more sensitive observation of (19)F metabolite maps of 5-FU and other (19)F-containing compounds that have relatively long relaxation times.

Magnetic Resonance Cisternography

PURPOSE

To assess the detectability of the inner ear structures using both 3-dimensional (3D) balanced fast-field echo (bFFE) and 3D driven equilibrium (DRIVE) sequences in conjunction with parallel imaging and to compare the image quality of those sequences.

MATERIALS AND METHODS

Thirty-eight healthy volunteers were examined using a 1.5-T magnetic resonance unit. The 3D bFFE and the 3D DRIVE sequences were compared. The relative contrast between the cranial nerves and the cisternal space was calculated. The detectability of the cranial nerves and the cochlear and semicircular canals was graded on a 3-point scale (1, poor; 2, fair; 3, excellent).

RESULT

The relative contrast for the cranial nerve in 3D bFFE and 3D DRIVE was 4.31 +/- 1.53 and 5.73 +/- 4.60, respectively. The 2.5 turns of the cochlea, spiral lamina, and all 3 semicircular canals were better visualized using the 3D DRIVE.

CONCLUSION

The 3D DRIVE is superior to the 3D bFFE in evaluation of the structures of the inner ear.

Use of ultra-high-resolution data for temporal bone dissection simulation

OBJECTIVES

For the past 5 years, our group has been developing a virtual temporal bone dissection environment for training otologic surgeons. Throughout the course of our development, a recurring challenge is the acquisition of high-resolution, multimodal, and multi-scale data sets that are used for the visual as well as haptic (sense of touch) display. This study presents several new techniques in temporal bone imaging and their use as data for surgical simulation.

METHODS

At our institution (OSU), we are fortunate to have a high-field (8 Tesla) magnetic resonance imaging (MRI) research magnet that provides an order of magnitude higher resolution compared to clinical 1.5T MRI scanners. Magnetic resonance imaging has traditionally been superb at delineating soft tissue structure, and certainly, the 8T unit does indeed do this at a resolution of 100-200 microm(3). To delineate the bony structure of the mastoid and middle ear, computed tomography (CT) has traditionally been used because of the high signal-to-noise ratio delineating bone signal from air and soft tissue. We have partnered with researchers at other institutions (CCF) to make use of a "microCT" that provides a resolution of 214 x 214 x 390 micrometers of bony structure.

RESULTS

This report provides a description of the 2 methodologies and presentation of the striking image data capable of being generated. See images presented.

CONCLUSIONS

Using these 2 new and innovative imaging modalities, we provide an order of magnitude greater resolution to the visual and haptic display in our temporal bone dissection simulation environment.

Registration and Fusion of CT and MRI of the Temporal Bone

OBJECTIVE

To present and evaluate a registration method to fuse complementary information of CT and MRI of the temporal bone.

METHODS

CT and MRI of the temporal bone of 26 patients were independently registered 4 times. A manual, iterative, intrinsic, rigid, and retrospective registration method was used. Mean CREm (consistency registration error) was calculated as a reproducibility measurement.

RESULTS

CREm was 0.6 mm (95% CI = 0.52-0.68 mm). T-test revealed no difference between pathologic and normal cases (t[102] = -1.71; P = 0.09). Time needed: 13 minutes. In the registered and fused datasets, important bony surgical landmarks (eg, facial nerve canal, inner ear) could be assessed in 3 dimensions relatively to tumor tissue (eg, acoustic schwannoma). Fluid distribution within partially obliterated cochleae could be assigned to either scalae.

CONCLUSION

An accurate, reproducible registration and fusion method that improves tumor surgery and cochlea implantation planning with only minor changes to the clinical workflow was presented and described. We suggest this method in selected cases.

Pediatric and adult cochlear implantation

The frequency of cochlear implantation has increased tremendously over the past decade. Cochlear implantation is often performed as an outpatient procedure and is considered an acceptable treatment for severe to profound sensorineural hearing loss in patients who are refractory to conventional hearing augmentation. Imaging plays an important part in the work-up of cochlear implant candidates, and an understanding of imaging evaluation procedures is essential. The radiologist must be familiar with imaging findings that contraindicate implantation (absence of the cochlea or cochlear nerve) and with those that could significantly alter surgery (facial nerve dehiscence, cochlear ossification). It is also imperative to be familiar with the growing number of imaging options (particularly magnetic resonance [MR] imaging pulse sequences) to optimize evaluation of cochlear implant candidates. Imaging choices will be substantially influenced by the manufacturer of the computed tomographic scanner or MR imager. Radiologists will assume an expanding role in evaluating affected patients as the frequency of cochlear implantation continues to increase.

[Evaluation of the increase in signal intensity from applying the fast recovery technique to fast spin echo images]

The aim of the present study was to evaluate the increase in signal intensity caused by applying the fast recovery (FR) technique to fast spin echo (FSE) images, that is, the fast recovery fast spin echo (FR-FSE) method. All images of phantoms, whose T(2) values were different, were acquired with a Signa 1.5 Tesla system (GE Medical Systems) using the three-dimensional (3D) FSE and 3D FR-FSE sequences. We assessed the increased signal intensity as follows: (signal intensity on the FR-FSE image - FSE image) / FSE image (%). Our results showed that the increased signal intensity became high when 1) T(2) of the phantom was prolonged, 2) TR was shortened, and 3) echo train length (ETL) was decreased. By utilizing the results of this study, the increased signal caused by the FR technique could be estimated quantitatively when the TR, ETL, and T(2) of investigated substances were determined. For example, when TR, ETL, and T(2) were 1500 msec, 16-64, and 1500 msec, respectively, the increase in signal intensity was estimated to be approximately 70%. In addition, when T(2) was less than approximately 250 msec, signal intensity was not significantly increased by the FR pulses, that is, the FR-FSE image was the same as the FSE image. Accordingly, the FR-FSE method was confirmed to enhance the signal in substances with longer T(2), while maintaining the same contrast of the image as that obtained by the conventional FSE method. Our results are useful for evaluating the increased signal intensity caused by employing the FR technique.

Hybrid phased array for improved internal auditory canal imaging at 3.0-T MR

PURPOSE

To develop and evaluate a hybrid phased array for internal auditory canal (IAC) imaging at 3.0 T.

MATERIALS AND METHODS

A hybrid phased array was designed and built as two circular surface receive-only coils combined with a volume transmit-receive birdcage head coil for simultaneous image acquisition. Phantom and volunteer images were obtained to assess the coil performance.

RESULTS

The phantom data show that significant signal-to-noise ratio (SNR) improvement was achieved in the region corresponding to the inner ear, i.e., by a factor of 2.5 compared to the standard head coil data. Volunteer IAC image quality was deemed superior as compared to images acquired at 3.0 T using a standard head coil.

CONCLUSION

This hybrid array combined with three-dimensional fast spin-echo (FSE) acquisition resulted in improved high spatial resolution IAC imaging.