University of Michigan continues fine-tuning neuro ExamCards

Transcription

1 I s s u e M a rc h F i e l d Strength Publication for the Philips MRI Community University of Michigan continues fine-tuning neuro ExamCards Drs. Mukherji, Parmar create Achieva 3.0T ExamCards for complex cases This article is part of Field Strength Issue 31 March 2007

2 University of Michigan continues finetuning neuro ExamCards for Achieva 3.0T Neuroradiologists create optimized ExamCards for complex neuro cases Hemant Parmar, M.D., Suresh Mukherji, M.D. and Nancy Dudek, R.T. 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. Aneurysm. Scanned with MOTSA COW ExamCard. MIP 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 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 mm to 512 x 800 mm 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. 10 Field strength Issue 31 - March 2007

3 T2w SENSE T1w fat suppressed 3D T2w DRIVE 3D T2w DRIVE T1w TSE Left cranial nerve V schwannoma. Scanned with skull base ExamCard. Right cochlear nerve schwannoma. Scanned with IAC 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. 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. For cochlear implant candidates, oblique sagittal reformats of the 3D T2 DRIVE images help clinicians distinguish each of the four cranial nerves in the IAC, encompassing the cochlear and vestibular nerves. If a healthy cochlear nerve isn t there due to pathology, there s no point in performing a cochlear implant, Dr. Mukherji observes. 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 Issue 31 - March 2007 Field strength 11

4 SmartExam enhances operational efficiency Since January 2006, the University of Michigan Health Center has been using Philips SmartExam technology to improve MR workflow and increase the precision of inter- and intra-patient examinations on its Achieva 3.0T system. The computational speed of SmartExam s planning algorithm and rapid scan execution with ExamCards are making a significant impact, according to UM clinicians and technologists. SmartExam is available for Achieva 3.0T, Achieva 1.5T, Intera 1.5T and Panorama 1.0T scanners. It also will become available as an upgrade for most Philips MR systems installed since For technologists with moderate or intermediate skills who are planning the more complex studies such as cranial nerve examinations SmartExam saves a lot of time, says Nancy Dudek, lead technologist. Dudek adds that SmartExam frees up technologist time to interact more closely with the patient. Before SmartExam, technologists tended to focus virtually their complete attention on planning slice positions and little on monitoring the patient, she says. Most patients like it if you talk to them it makes them more comfortable. SmartExam enables technologists to develop a rapport with patients. I like the consistency of the image quality on SmartExam studies both between patients and for successive scans of the same patient, says Suresh Mukherji, M.D., UM Chief of Neuroradiology says. It helps me be a better neuroradiologist because the slice angles are always the same between scans. For example, if you wanted to know whether an MS patient was getting better or worse you need to evaluate the exact same slices through time. SmartExam enables us to do this so we can more accurately determine lesion burden. More time for tasks requiring human intelligence According to Dudek, because SmartExam relieves technologists of time-consuming manual planning and scanning, it enables them to spend more time on tasks such as post-processing, which often requires the insight of the human operator. In turn, this helps them improve the overall quality of work. If you re post-processing an MRA, you have to take care to avoid cutting out parts of arteries while you re cutting out fat and tissue that you re not interested in, she says. With SmartExam, the technologist has the time to concentrate on post-processing, resulting in a better job with less likelihood for errors. This makes it much easier for the radiologists to read the results. in a millimeter in size, Dr. Parmar says. We are excited that we can actually start seeing these structures. 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 mm to 256 x 512 mm 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. T1 SE T1 SE dynamic T1 post-contrast 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. Left pituitary microadenoma. Scanned with pituitary ExamCard. 12 Field strength Issue 31 - March 2007

5 3D SENSE 3D SENSE 3D SENSE Patient scanned with TLE ExamCard. No lesions were found. T1w IR CLEAR T2w TSE SENSE T2w FLAIR SENSE 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. 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. "The specificity of each ExamCard is an effort to zero in faster and with more diagnostic precision on the patient s problem" Net Forum w w w. p h i l i p s. c o m /n e t f o r u m Visit the NetForum User Community for viewing more 3.0T articles, clinical cases, application tips or downloading 3.0T ExamCards. Issue 31 - March 2007 Field strength 13