Introduction

MR Protocols for Central Nervous System (CNS) MR Imaging

Central Nervous System (CNS) MR Imaging Protocols were developed by an expert consensus panel for use on Philips MR systems.

These protocols provide field strength‐specific parameters for 1.5T and 3T. Attention has also been given to patient preparation, exam streamlining, special notes on coil choice and placement, and making the best use of Vueway/Elucirem (gadopiclenol), a recently FDA‐approved, high‐relaxivity, extracellular gadolinium‐based contrast agent (GBCA).

The consensus panel consisted of the following experts in radiology:

Matthew White, MD and Candice M. Maack, RT(R)(MR)(CT) – University of Washington School of Medicine, Seattle, Washington
Mahmud Mossa-Basha, MD, DABR and Noah Briller, RT(R)(MR)(CT) – University of Washington School of Medicine, Seattle, Washington

The MR imaging protocols for CNS presented here include individual sets optimized specifically for 1.5T and 3T systems on Ingenia software release 5.6. The sequences provided are specialized and may be intended for use with reduced field of view to better assess particular structures. They may be used on their own, or combined with basic sequences to provide a more comprehensive study.

The imaging parameters that are listed can generally be modified to work with other releases and platforms, in most cases requiring only small adjustments that should be within the capabilities of a knowledgeable technologist. However, scan times may increase slightly in some circumstances—for instance, when parallel imaging (SENSE) is not available.

• Brain
  • Comprehensive Brain 3T
  • Multiple Sclerosis Brain 1.5T and 3T
  • Tumor Brain 3T
  • Brain Magnetic Resonance Venography (MRV) 3T
  • Seizure Brain 1.5T and 3T
• Specialty Brain
  • Pituitary 1.5T and 3T
  • Internal Auditory Canals 1.5T and 3T
• Head and Neck
  • Orbits 1.5T and 3T
  • Neck Soft Tissue 1.5T and 3T
  • Maxillofacial 1.5T and 3T
• Spine
  • Cervical Spine With/Without IV Contrast 1.5T and 3T
  • Thoracic Spine With/Without IV Contrast 1.5T and 3T
  • Lumbar Spine With/Without IV Contrast 1.5T and 3T

Imaging protocols for the brain should utilize at a minimum an 8 channel head coil and SENSE parallel imaging techniques to optimize SNR while minimizing imaging time. Dedicated spine coils should be used for spine exams. A dedicated neurovascular coil should be used for angiography imaging and imaging of the soft tissue in the neck unless a dedicated neck coil is available. Some Philips platforms are supplied with dStream integrated head-and-spine or head-neck-spine coil systems that can be used instead of standard coils. Each protocol contains a brief summary of study-specific patient preparation, notes on coil choice, and recommendations for contrast dose and administration. Wherever appropriate, optional scan sequence descriptions are included that may be either substituted for or added to the listed protocol for special clinical circumstances.

General Notes

• Brain imaging. T1-weighted images postcontrast should generally be acquired in multiple planes. These can be acquired as 2D image sets in multiple planes or as a single 3D image set that is reformatted to display the additional planes. Both options are provided in the various protocols and may be used interchangeably according to the clinical indication. Fat saturation may be added to postcontrast T1 images to provide better visualization of skull-base lesions or bony metastases. T2 FLAIR images can be acquired as a pseudo 3D image set by using very thin (1.5 mm) slices and then reformatting them into orthogonal planes, or performed as a 3D acquisition with multi-planar reformats. This approach is especially useful in cases of trauma and in multiple sclerosis (MS) patients
• MS patients. MS patients are evaluated with an additional Sagittal FLAIR, 3D FLAIR or with a pseudo 3D FLAIR sequence that is then reformatted in the Sagittal plane for better evaluation of callosal plaques and periventricular “Dawson fingers.” Not uncommon, some MS patients are evaluated and followed with both brain and cervical spine imaging to evaluate the total plaque load in these 2 regions. If this combination is planned, the 16 channel neurovascular array, which can provide great brain and cervical spine imaging, then becomes the preferred RF coil
• Spine imaging. Cervical, thoracic, and lumbar imaging all use Sagittal and Axial T1- and T2-weighted sequences. TSE short tau inversion recovery (STIR) imaging is valuable for detection of bone abnormalities and intramedullary lesions and for evaluation of ligamentous injury in trauma patients. Postcontrast Sagittal and Axial images are performed with a fat saturation technique using an adiabatic RF saturation pulse (SPAIR) whenever possible

General Notes Relevant for All Neurological Evaluations by MR Imaging

• Contrast. To optimize visualization of disorders of the blood‐brain barrier, most neurologic examinations with contrast are acquired at least 3 to 5 minutes after injection. In most cases, the method of injection is not important, and a slow bolus injection may be administered either manually or with an injector. Dosing of gadopiclenol is weight‐based and at 0.05 mmol/kg (half the dose of other extracellular agents) for most protocols aimed at standard extracellular fluid (ECF) distribution. The dose for an individual injection may be lower for split‐dose protocols (e.g. involving multiple first‐pass MRA acquisitions), keeping overall dose within the standard 0.05 mmol/kg guideline. The ACR has recommended that the lowest dose feasible be used for diagnostic purposes; because standard dosing recommendations are mostly influenced by lean body mass, and ECF volume in fatty tissues is low, it is reasonable to cap the upper limit of gadopiclenol for heavier adults at 15 mL total (the largest single‐dose vials and pre‐filled syringes are 15 mL)
• Susceptibility. A T2-weighted gradient echo sequence or 3D susceptibility-weighted imaging (SWI) can be used to detect blood products and microhemorrhages. This approach is especially useful in cases of possible stroke and in trauma patients
• Diffusion. Most brain protocols include a diffusion-weighted imaging sequence that is useful for evaluation of stroke, infection, and tumor. Apparent diffusion coefficient (ADC) maps should be included to evaluate actual diffusion properties and eliminate misinterpretation of T2 shine-through
• Perfusion. Perfusion-weighted imaging is increasingly used in stroke and tumor imaging to visualize ischemia versus penumbra. In patients with cerebral tumors, the level of perfusion before treatment correlates with tumor aggressiveness and prognosis, whereas the level of perfusion after treatment correlates with neoangiogenesis and thereby helps to distinguish tumor recurrence or progression from radiation necrosis. Good perfusion imaging requires a very rapid bolus injection (4-5 mL/sec) through a large-gauge IV (preferably 18-Ga) needle placed in the antecubital fossa. It should be noted that high-relaxivity agents also increase T2* relaxivity. Thus, to increase the susceptibility of the contrast bolus and to produce the best perfusion maps with a single dose of contrast, high-relaxivity agents should be considered