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Head and Neck ExamCards - General Hospital St. Jan, Brugge

Best Practice
Casselman, Jan, M.D., Ph.D. Brugge, AZ St. Jan AV Belgium

Although the brain is the head's most prominent organ, there is much more to image at the top of the body than just the cerebrum and cerebellum. Outside of the braincase are the subjects of head and neck MRI: the skull base, cranial nerves, ears, orbits and neck. At General Hospital St. Jan (Brugge, Belgium), radiologist Dr. Jan Casselman is creating a battery of ExamCards that will account for virtually every head and neck MRI study possible. This Master Class set of head and neck ExamCards emphasizes SENSE, CLEAR and close-to-the-skin positioning of surface coils.


Dr. Jan Casselman General Hospital St. Jan (Brugge, Belgium)
Dr. Jan Casselman
General Hospital St. Jan (Brugge, Belgium)

General Hospital St. Jan developing Master Class ExamCards to image diverse region

General Hospital St. Jan is creating at least 15 ExamCards to encompass the diverse anatomy of the head and neck region. Even then, individual ExamCards will vary little, with respect to pulse sequences, due to the imperatives in head and neck imaging to gather maximum signal and homogenize image appearance, according to Jan Casselman, M.D., Ph.D., Clinical Director of MR and Head and Neck Imaging and Chairman of the Department of Radiology.
"All head and neck imaging at St. Jan involves two critical things," he says. "You have to position coils close to the skin and use SENSE or CLEAR. In this way, high resolution images can be acquired in an acceptable time. Other than that, pulse sequences are - with some exceptions - the classic T1- and T2-weighted sequences."
The customary approach for temporal bone, orbits, oral cavity, nasopharynx and salivary glands is to use the SENSE Head/Neck coil to provide an initial overview of the brain or soft tissues of the face and neck, followed by a close-in survey with Flex-S coils (on the ears, mouth, orbits, etc.) positioned next to the skin within the enclosure of the larger coil. The Flex-S coils return maximum signal by virtue of their proximity to the region-of-interest.
"If I used the head and neck coil alone, its detectors are four centimeters from the skin, which causes tremendous signal loss. Even 3.0T probably would not recover that lost signal," he observes. "Since the Flex-S coils are linked, you can also use both SENSE and CLEAR. CLEAR is fantastic because it allows signal homogenization from left to right without a drop-off at the center. With SENSE and CLEAR you can also acquire 1024-matrix images - with excellent SNR and image detail, for anatomy such as the orbits and ears - in just four minutes."  In the inner ear, strong signal combined with a high-resolution matrix helps clinicians distinguish small nerves and the structures of the cochlea, such as the scala tympani and scala vestibuli. In the orbits, high SNR and matrix are necessary to resolve the tiny muscles on the globe of the eyeball and the optic nerve at its entrance to the globe.

Larynx imaging reveals organ's varied anatomy

Imaging of laryngeal anatomy requires some manipulation of Flex-S coils (within the SENSE Head/Neck coil) to optimize signal, Dr. Casselman indicates. "They need to form a collar around the neck," he says. "I even use tape to fix them closer to the neck. The images are far superior to those we've acquired in the past, when we could hardly see the larynx due to low signal and low spatial resolution. We would lengthen sequences to five or six minutes to build signal and resolution, but eventually patients would swallow. Now, we have so much signal that we can reduce scan time to two minutes, or, alternatively, increase scan time to 3.5 minutes in cooperative patients to provide even higher resolution.
With these techniques, we can acquire excellent images that show not only the vocal cords, but also the muscles and ligaments that compose them, as well as ossified and non-ossified cartilage - you can see everything. At General Hospital St. Jan, our surgeons no longer want CT scans of the larynx."
St. Jan's surgeons rely on larynx MRI images to inform interventional choices. For example, if laser therapy is an option, surgeons will want to know the extent of tumor invasion in the muscle to determine if they can still ablate it. Similarly, if cartilage invasion is identified, then surgery is no longer an option and is replaced by possible total laryngectomy. MRI with close-fitting, Flex-S coils positioned bilaterally on the cheek produces superb images to assist in staging tumors in the oral cavity, Dr. Casselman adds. "You will see cortical bone invasion on CT, but not the extent of invasion; it can be five centimeters in and you don't see anything on CT."
With flexible surface coils positioned slightly more posteriorly, St. Jan radiologists image the salivary glands using a 1024 matrix. The most common tumor of the salivary glands is a pleomorphic adenoma (benign mixed tumor). In imaging studies of either the larynx or oral cavity, Dr. Casselman emphasizes that while tumor detection and staging are the primary goals, the final sequence employs the SENSE Head/Neck coil in a coronal sequence covering the entire neck from the skull base to the thoracic inlet and enabling lymph node staging.
1.5T Master Class ExamCards Head & Neck - General Hospital St. Jan, Brugge


Inner ear imaging requires tailored approach

General Hospital St. Jan has developed ExamCards for IAC Routine, IAC Vertigo and IAC Tinnitus, which are available on Philips' NetForum for immediate download to eligible users.


IAC Routine ExamCard

The IAC Routine ExamCard for investigation of hearing loss uses the SENSE Head coil and implements a T2-weighted sequence of the brain to exclude tumor. Subsequently, bilateral Flex-S coils are used and a T2- weighted DRIVE sequence is applied to obtain ultra-high resolution images of small inner ear anatomy, such as the nerves. Use of SENSE is necessary to maintain a reasonable scan time when using a 1024 matrix. The third and final sequence - a 3D, T1-weighted, contrast-enhanced PCA sequence - focuses again on the inner ear and on the cerebropontine angle to exclude enhancing lesions, labyrinthitis and meningeal enhancement.


IAC Vertigo ExamCard

The IAC Vertigo ExamCard adds a high resolution scan to evaluate the brain stem and posterior fossa, where the pathology responsible for vertigo often is found. "Equilibrium changes can usually be traced to nuclei in the brain stem or in the afferent or efferent vestibular pathways in the posterior fossa," Dr. Casselman notes. "The selective proton density T2-weighted sequence ensures we don't miss any infarction, tumor or MS in that area." A recent addition to the IAC Vertigo ExamCard for older patients is a diffusion sequence to improve the likelihood of detecting an acute infarction in the posterior fossa, one of the most frequent causes of acute vertigo.

IAC Tinnitus ExamCard
The IAC Tinnitus ExamCard covers patients with suspected tinnitus, the subjective or objective perception of sound. In addition to the routine T2-weighted brain survey, DRIVE and T1-weighted PCA sequences, IAC Tinnitus employs an MRA sequence with and without contrast to evaluate posterior fossa vessels. "The MRA sequence can reveal vascular lesions, such as glomus tumors, which can cause tinnitus as well as other possible vascular causes of tinnitus, including meningiomas around the temporal bone, dural fistulas and carotid dissections," Dr. Casselman says.
The IAC Tinnitus ExamCard may also be refined in the near future with the addition of a BOLD fMRI sequence. "If you compare people with tinnitus with the normal population, tinnitus sufferers have less activation - from the perceived sound - on the contralateral cortex where in normals you expect activation. In effect, the tinnitus has saturated the contralateral side with sound, so activation migrates to adjacent same-side areas, an effect we can see with BOLD fMRI," he explains. "Therefore, it is easier to confirm if the patient has tinnitus and to identify on which side to direct treatments, such as extracorporeal magnetic stimulation."

Middle ear is site of most common pathology

The most frequent examined middle ear pathology is cholesteatoma, which eventually can completely destroy the ossicles of the middle ear and can subsequently affect the inner ear, resulting in complete deafness. With CT, it is often impossible to confirm the presence of a cholesteatoma in a completely obliterated middle ear, but with specific MRI sequences and Flex-S coils, definitive diagnoses can now be made, Dr. Casselman maintains.
"The two most important sequences are a late-enhancement T1 sequence and a non- EPI diffusion sequence," he says. "If no enhancement is noted after 45 minutes, the lesion is likely a cholesteatoma, unless the lesion under study is a cyst. To rule out a cyst, the diffusion sequence is run and if there is high diffusion signal at a b-value of 1000 then that indicates a cholesteatoma - because cysts have high ADC and thus low signal on the b-1000 images."
In the past, the inability to discern between cholesteatoma and other middle ear pathology compelled exploratory surgery for all patients whose CT scan merely showed an obliterated middle ear with no convincing evidence of a potentially aggressive lesion. "Even more interesting, patients whose middle ear damage was from a cholesteatoma need second-look surgery 6-12 months post-operatively," Dr. Casselman notes. "However, for all cholesteatoma patients, recurrence is less than 10%, so 90% of patients are operated on for nothing. An MRI study specifically geared to help doctors detect cholesteatoma could help reduce the major costs and invasiveness involved in unnecessary second-look surgery."

Microcoils improve "close-to-the surface" head and neck studies

At St. Jan, the preferred RF coils for head and neck studies are the flexible SENSE Flex-S coils, which provide excellent SNR even for centerline anatomy when placed close to the skin. However, when high resolution is needed to visualize known, close-to-the-surface pathology or anatomy, such as nerves, TMJ joint or eyeball, Dr. Casselman uses Philips' 47 mm Microscopy coil.

"We don't even need to use a 2048 matrix, because we can significantly reduce slice thickness and FOV," he says. "So, if I 'smear out' the 1024 matrix over a very small FOV, I can get very high resolution. For example, we acquired some beautiful images of the globe of the eye in which we think we can see the retina. Or, we can visualize the branches of the facial nerve that enter the parotid gland. You can't see this anatomy with regular coils."




Clinical cases will soon be added on NetForum:

- Tumor in oral cavity

- Vocal cord tumor

- Left-sided tinnitus

- Choleastoma



This content has been made possible by NetForum Community.
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May 11, 2006

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