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University of Michigan finetuning Achieva 3.0T neuro ExamCards

Best Practice
Prof. Mukherji, Suresh, M.D. Ann Arbor, University of Michigan USA
Dr. Parmar, Hemant, M.D. Ann Arbor, University of Michigan USA
Mrs. Dudek, Nancy, R.T. Ann Arbor, University of Michigan USA

University of Michigan continues finetuning Achieva 3.0T neuro ExamCards

Clinicians at the University of Michigan (UM) Health Center (Ann Arbor, Mich., USA) have been optimizing five Achieva 3.0T neuro ExamCards, creating UM's neuro Master Class ExamCards for MRA of the circle-of-Willis, pituitary, cranial nerve VIII (IAC) and V (skull base) and temporal lobe epilepsy. These five protocols were designed based on patients' presenting symptoms to sharpen the focus on the abnormal area. For example, implementing the cranial nerve V ExamCard for trigeminal neuralgia, instead of the comprehensive brain protocol, increases the MR study's "diagnostic yield" and avoids recalls, says Dr. Hemant Parmar, UM neuroradiologist.

Neuroradiologists create optimized ExamCards for complex neuro cases

Nearly half of University of Michigan (UM) Health Center's daily volume of about 123 neuro MR (brain, spine, head & neck) cases are steered to the institution's Achieva 3.0T system - versus its 1.5T scanner - to take advantage of the 3.0T system's higher SNR for complex cases. Five areas in particular, circle-of-Willis, IAC, skull base, pituitary and scans to evaluate epileptogenic foci merited creation of a set of ExamCards.


The specificity of each ExamCard is an effort to zero in faster and with more diagnostic precision on the patient's problem, says Hemant Parmar, M.D., UM neuroradiologist. "As radiologists, we can't supervise each and every case and employ all the sequences we have at our disposal," he remarks. "To get the right information in the 45-60 minute time slot, we need to maximize the information we obtain for a particular study. To that end, we need to instruct our referring physicians to precisely specify the patient's presenting symptoms, so we can isolate the area of the brain we need to study and apply the appropriate ExamCard."

Tuned-up ExamCard sharpens focus in circle-of-Willis imaging

When UM clinicians shifted many of their circle-of-Willis MRA cases from their 1.5T imager to Achieva 3.0T, they assumed they would be obtaining considerably better quality images due to the SNR boost alone. "The ExamCard for Achieva 3.0T specified many of the same imaging parameters for circle-of-Willis that we were using at 1.5T, so we weren't particularly happy because we wanted the 3.0T MRAs to look different and provide more information than 1.5T," Dr. Parmar says.


Accordingly, he adds, for the Achieva 3.0T ExamCard for the circle-of-Willis, they increased the 3.0T matrix from 256 x 192 to 512 x 800 and reduced the slice thickness from 0.7 mm to 0.6 mm. Clinicians also employed the 8-channel SENSE Head coil, enabling the use of SENSE to avoid incurring additional minutes on the time-of-flight sequence.


"With this 3.0T Brain MRA ExamCard, we can see structures previously not visualized at 1.5T and even subtle differences we didn't appreciate on the original ExamCard, such as small aneurysms, small vascular malformations, tertiary branches and vessels with better clarity," adds Suresh Mukherji, M.D., UM Chief of Neuroradiology.

Aneurysm. Scanned with MOTSA COW ExamCard.

ExamCard seeks information on many skull base pathologies

UM physicians apply the Cranial Nerve V ExamCard for patients with trigeminal (fifth) nerve pathologies, suspected cavernous sinus and Meckel's cave abnormalities, suspected clival diseases and suspected perineural tumor spread.


"Whenever we use this protocol we are looking for very specific information at the base of skull," he says. "At 3.0T, we modified the ExamCard to reduce slice thickness, because we are dealing with very thin structures, such as cavernous sinuses, Meckel's cavity and branches of the fifth nerve - so we need high resolution images with a smaller FOV."


Clinicians also added an T2-weighted axial 3D DRIVE sequence to enhance visualization of the cisternal segments of the trigeminal nerve. "If there is a lesion along that nerve segment, the T2 DRIVE sequence helps us to define it much better against the bright CSF background," Dr. Parmar notes. "Additionally, for this particular application, it is far better than any of the other axial T2 sequences we run, because it's a 3D sequence that provides submillimeter resolution and enables multiplanar reformatting."


The Cranial Nerve V ExamCard also is useful below the skull base, such as in the upper masticator space and even for imaging paranasal sinus abnormalities, he adds.

T2w SENSE T1w fat suppressed
T1w fat suppressed
T1w TSE Post contrast
Post contrast
Left cranial nerve V schwannoma. Scanned with skull base ExamCard.

IAC-level structures visualized with Cranial Nerve VIII ExamCard

Just a few slices inferior to the Cranial Nerve V imaging zone, UM's Cranial Nerve VIII ExamCard focuses on visualization of IAC structures and pathology and on other anatomy in the IAC region. This ExamCard is applied for patients with sensorineural hearing loss due to suspected acoustic neuroma; other cerebellopontine angle tumors; atypical Bell's palsy; and suspected membranous labyrinth abnormalities. The Cranial Nerve VIII ExamCard also is used for pre-cochlear assessment of the cochlear nerve and in cases of hemi-facial spasms.


UM radiologists also optimized this ExamCard by adding the axial T2-weighted 3D DRIVE sequence. "We see very subtle differences on the DRIVE sequence that we would not have seen on other sequences," Dr. Parmar says. "A patient here had three scans on the 1.5T system where the patient's symptoms were attributed to a schwannoma arising from the vestibular nerve, the most common point of origin for these tumors. Based on the DRIVE sequence on Achieva 3.0T, however we were able to determine that the tumor was originating from the cochlear nerve."


The alternative to T2 DRIVE, he adds, is to perform a separate sequence through the IAC in the oblique sagittal plane. "Using DRIVE avoids the need to do a separate sequence - we just reformat in the angle we want and still get the same information."


Using its Achieva 3.0T and the Cranial Nerve VIII ExamCard, UM clinicians hope to study the anatomy of the membranous labyrinth in more detail than ever


"We were not aware that we would one day see this structure, which is less than in a millimeter in size," Dr. Parmar says. "We are excited that we can actually start seeing these structures."

Post contrast Post contrast
Post contrast
Post contrast
Right cochlear nerve schwannoma. Scanned with IAC ExamCard.

ExamCard for pituitary features high-resolution, small FOV

Imaging of the sella tursica and pituitary gland requires high-resolution and a small FOV to appreciate small structural pathology, such as micro- or macroadenomas; suspected suprasellar or hypothalamic masses; and abnormalities of the optic chiasm or infundibular stalk.


UM clinicians optimized the original Exam Card for this application by increasing the matrix from 256 x 192 to 256 x 512 and employing a smaller FOV (18 cm), and by reducing the slice thickness from 3 mm to 2 mm. They also reduced the flip angle on the spin echo sequences from 90° to 70° to increase the grey-white differentiation and reduce SAR. "In the pituitary, the main issue is to obtain higher resolution in a very small area of the brain," Dr. Parmar says. "There are so many interrelated structures in this region, including the optic chiasm, the infundibular stalk and the pituitary gland per se. And there is the hypothalamic regions. All these areas need to be studied in detail when patients come in with specific complaints."


UM neuroradiologists are not necessarily seeing pathology they wouldn't have encountered before using the previous ExamCard, but their diagnostic confidence is higher with the optimized version, he adds.

T1SE T1 SE dynamic T1 post-contrast
T1 SE dynamic
T1 post-contrast
Left pituitary microadenoma. Scanned with pituitary ExamCard.

Grey/white differentiation is key in temporal lobe epilepsy cases

Assessing the presence and extent of cortical dysplasia associated with temporal lobe epilepsy (TLE) depends on the ability to differentiate grey matter from white matter, Dr. Parmar notes. While the University of Michigan's Achieva 3.0T TLE ExamCard is not unlike other TLE protocols in the sequences it employs, the coronal 3D FFE sequence (scan 8 of 10) has been modified to increase grey/white differentiation. This change helps surgeons discern areas of abnormality and is one step closer to the ultimate assessment using surface coil imaging of targeted (e.g., left frontal lobe only) regions.


"With the 3D FFE sequence, we wanted to match the degree of inherent grey/white differentiation that we routinely see in the inversion recovery sequences [scans 9, 10], which provide images that appear as close to actually seeing a cut brain section as possible," Dr. Parmar observes. "We were able to make this modification on the TLE ExamCard for UM's Achieva 3.0T with the help of a former Philips physicist, Dr. Xavier Golay. We worked together in Singapore at the National Neuroscience


Institute on an Achieva 3.0T system and he made a similar modification to that sequence, which I simply appropriated for our 3D FFE sequence. And, we have a reciprocal arrangement with that site."


"In addition, on all sequences, the slice thickness was increased from 0.9 mm to 1.0 mm," he says. "They look smoother with 1.0 mm thick slices. Conversely, the coronal T2-weighted and coronal FLAIR sequences [scans 6-7] use a higher matrix in this Achieva 3.0T ExamCard to facilitate study of small hippocampi."

Patient scanned with TLE ExamCard. No lesions were found.

Neuro ExamCard list to grow

These initial five neuro ExamCards represent a fraction of the number the University of Michigan Health Center will ultimately refine for use with Achieva 3.0T. "Our standards are extremely high, so these five are the ones we are completely satisfied with the results we're getting," Dr. Mukherji says. "Obviously, for this ExamCard series to be complete, we are concentrating intensely on refining our cranial nerve ExamCard and even the routine standard brain imaging ExamCard. The spine ExamCard also is being developed - but we're working on it and we're progressing."




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May 22, 2007

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Best Practice
Achieva 3.0T
Release 1, Release 2
Quasar, Quasar Dual
Brain, Brain stem, IAC, Neuro, Pituitary, Vascular

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