Teslascan Enhanced Hepatobiliary MR Imaging Technique

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Teslascan is an isotonic, clear, yellow solution that is available as a ready-to-use formulation at a concentration of 0.01 mmol/ml in 50ml glass vials. The clinical dose is 5 µmol/kg body weight, which equals 0.5 ml/kg body weight.  The mode of administration is intravenous infusion at a slow rate of 2-3 ml/min.

Prior to the administration of any contrast material, breath-hold axial and coronal half-Fourier acquisition single-shot turbo spin echo (HASTE) images are acquired using the following parameters: TR/effective TE/refocusing angle = ¥ /62 ms/140-160 ° , imaging matrix of 128-192 x 256, field of view 300 - 375 mm, 4 mm slice thickness, rectangular field of view depending on body habitus, 15 – 20 slices per breath hold . At least three oblique coronal heavily T2-weighted turbo spin echo imaging (TR/effective TE/flip angle, 2800/1100/150-180 ° , matrix 240 x 256, field of view 300-375 mm, 20-60 mm section thickness with optional rectangular field-of-view) is also performed, each within a single breath hold acquisition.

At the end of the routine MRCP exam, an intravenous injection of Teslascan at a standard dose of 5 m mol/kg (0.1 ml/kg, up to a maximum of 15 ml) is administered via a slow injection over 1 to 2 minutes followed by a 10 ml saline flush. Ten to 15 minutes after injection, axial and coronal volumetric 3D spoiled gradient echo acquisitions of the liver and biliary system is performed using two volumetric interpolated breath-hold exam sequences with intermittent fat-suppression pulses: a higher resolution sequence acquired coronally with limited coverage through the biliary ducts: TR/TE/flip angle = 6.8/2.3/25-40 ° , 128-256 x 512 matrix, 350-450 mm FOV using rectangular field-of-view depending on body habitus, 24 partitions interpolated to 48 slices with £ 1.5 mm thickness; and, a lower resolution sequence performed axially to include the entire liver: TR/TE/flip angle = 4.5/1.9/25-40 ° , 128-160 x 256 matrix, 300-375 mm FOV using rectangular field-of-view, and 80-112 partitions for £ 2 mm slice thickness (18) . Imaging time for all sequences is kept less than 25 seconds to facilitate breath-holding during the acquisition. Subsequent post-processing such as subtraction and multiplanar reconstructions can be performed on the post-Teslascan sequence for better delineation of hepatobiliary anatomy.

READ MORE:
Dynamic Coronal MRCP
Secretin-Enhanced MRCP Protocol
3D MRCP Pancreas Technique

MR Cholangiopancreatography (MRCP) PROTOCOLS

MRCP reference line for 3D biliary imaging

Random direction of nuclear spins outside a magnetic field.

(A) Random direction of nuclear spins outside a magnetic field.  When spins are placed in a large magnetic field (oriented here along the z axis), they begin to (B) precess about that direction and (C) slowly align themselves until (D) they are all aligned parallel to the applied field.  A radio frequency pulse coherently rotates these spins perpendicular to the applied field so that they (E) precess coherently, producing a detectable magnetic field.  Over time (F) the spins realign themselves with the magnetic field until they are again in the state shown in Figure D.

Dynamic MRI imaging of the TM joint

Current MR technology allows dynamic near-cinematic imaging of the disc. We have found that these studies have provided information additive to routine static imaging in some cases. 26 Advantages include a near real-time assessment of the true range of motion, shortduration of acquisition (35 seconds), and the ability to acquire imaging in a head coil without a dedicated jaw-opening appliance, which allows it to be included in most imaging protocols. Despite a reduced matrix, the disc and its relative position are well assessed . A side benefit of the half-Fourier acquisition single-shot turbo spino-echo (HASTE) imaging protocol is generally reduced susceptibility artifact, which can improve diagnostic yield in the setting of extensive dental hardware.
As imaging is performed in a direct sagittal plane, and not a sagittal oblique plane, the position of the disc is assessed by observing the intermediate zone. One expects its position to be interposed between the radial centers of the articular eminence and the mandibular condyle. In the setting of anterior disc displacement, the authors have seen dynamic imaging findings of visualization of reduction of disc material and of bulging of the anterior margin of the anterior band , even in cases where routine static imaging is normal. On dynamic imaging, a normal range of motion is present when the condyle has translated to the apex of the articular eminence. Normal individuals will often be able to translate beyond this point on a transient basis.

Read more:

Temporomandibular joint Anatomy(T-M Joint Anatomy)

MRI TM joint Benifits & Common Positive Findings
TM joint MRI Reference lines

TM Joint MRI Protocol

The frequency of Adverse Reactions Gadolinium-Based Contrast Media

The frequency of all acute adverse events after an injection of 0.1 or 0.2 mmol/kg of gadolinium chelate ranges from 0.07% to 2.4%. The vast majority of these reactions are mild, including coldness at the injection site, nausea with or without vomiting, headache, warmth or pain at the injection site, paresthesias, dizziness, and itching. Reactions resembling an “allergic” response are very unusual and vary in frequency from 0.004% to 0.7%. A rash hives, or urticaria are the most frequent of this group, and very rarely there may be bronchospasm. Severe, life-threatening anaphylactoid or nonallergic anaphylactic reactions are exceedingly rare (0.001% to 0.01%). In an accumulated series of 687,000 doses there were only 5 severe reactions. In another survey based on 20 million administered doses there were 55 cases of severe reactions. Fatal reactions to gadolinium chelate agents occur but are extremely rare.
Gadolinium chelates administered to patients with acute renal failure or severe chronic kidney disease can result in a syndrome of nephrogenic systemic fibrosis (NSF). (See the Chapter on Nephrogenic Systemic Fibrosis – NSF)

Extravasation of Gadolinium-Based Contrast Media

-->  The incidence of extravasation in one series of 28,000 doses was 0.05%. Laboratory studies in animals have demonstrated that both gadopentetate dimeglumine and gadoteridol are much less toxic to the skin and subcutaneous tissues than are equal volumes of iodinated contrast media. The small volumes typically injected for MR studies limit the chances for a compartment syndrome. For these reasons the likelihood of a significant injury resulting from extravasated MR contrast media is extremely low. Nonionic MR contrast media are less likely to cause symptomatic extravasation than hypertonic agents such as gadopentate dimeglumine.

The Safety of Gadolinium-Based Contrast Media (GBCM) in Patients with Sickle Cell Disease

Early in vitro research dealing with the effects of MRI on red blood cells (erythrocytes) suggested that fully deoxygenated sickle erythrocytes align perpendicularly to a magnetic field. It was hypothesized that this alignment could further restrict sickle erythrocyte flow through small vessels and, thus conceivably could promote vaso-occlusive complications in sickle cell patients . The further supposition that the IV administration of GBCM might potentiate sickle erythrocyte alignment, thereby additionally increasing the risk of vaso-occlusive complications, is mentioned in the FDA package inserts (as of 2009) for two GBCM approved for use in the United States (gadoversetamide [OptiMARK, Mallinckrodt] and gadoteridol [Prohance, Bracco Diagnostics]). To the best of our knowledge and noted in a review  of the literature, there has been no documented in vivo vaso-occlusive or hemolytic complication directly related to the IV administration of a GBCM in a sickle cell disease patient. A small retrospective study by Dillman et al with a control group showed no significantly increased risk of vaso-occlusive or hemolytic adverse events when administering GBCM to sickle cell disease patients . Additionally, several small scientific studies  of patients with sickle cell disease have employed MR imaging with GBCM without reported adverse effects. Therefore, it is our opinion that any special risk to sickle cell patients from IV administered GBCM at currently approved dosages must be extremely low, and there is no reason to withhold these agents from patients with sickle cell disease. However, as in all patients, GBCM should be administered only when clinically indicated.

Gadolinium-Based Intravascular Contrast Agents in Children

There are only a few published studies that address adverse reactions to IV gadolinium-based contrast media in children. The guidelines for IV use of gadolinium-based contrast agents are generally similar in both the pediatric and adult populations. There are currently six gadolinium-based contrast agents approved for IV use in the United States. These agents are commonly used “off-label” in children as several of these agents are not approved for use in pediatric patients and no agent is approved for administration to individuals less than two years of age. A few pediatric-specific issues regarding these contrast agents are discussed below.
Osmolality and Viscosity

--> As with iodinated contrast media, there is a significant range in osmolality and viscosity of gadolinium-based MR contrast agents. Osmolality of gadolinium-based contrast media ranges from approximately 630 mosm/kg H2O for gadoteridol (Prohance) to 1,970 mOsm/kg H2O for gadobenate dimeglumine (Multihance). Viscosities (at 37 degrees Celsius) range from 1.3 cps for gadoteridol (Prohance) to 5.3 cps for gadobenate dimeglumine (Multihance). These physical properties, however, are less important when using gadolinium-based contrast agents in children compared to iodinated contrast agents. The much smaller volumes of gadolinium-based contrast agents that are typically administered to pediatric patients’ likely result in only minimal fluid shifts. The slower injection flow rates generally used for gadolinium-based contrast agents result in lower injection-related pressures and decreased risk for vessel injury and extravasation.
Allergic-Like Reactions and Other Adverse Events
While rare, allergic-like reactions to intravascular gadolinium-based contrast media in children do occur. A study by Dillman et al  documented a 0.04% allergic-like reaction rate to these contrast agents in children. While mild reactions are most common, more significant reactions that require urgent medical management may occur . Pediatric allergic-like reactions to gadolinium-based contrast media are treated similarly to those reactions to iodinated contrast agents. A variety of physiologic side effects may also occur following administration of gadolinium-based contrast media, including coldness at the injection site, nausea, headache, and dizziness (see package inserts). There is no evidence for pediatric renal toxicity from gadolinium-based contrast media at approved doses. Extravasation of gadolinium-based contrast media is usually of minimal clinical significance because of the small volumes injected.
Nephrogenic Systemic Fibrosis (NSF) and Gadolinium-Based Contrast Media
There are only a small number of reported case of NSF in children (fewer than 10 as of 2008), the majority of which were described prior to this condition’s known apparent association with gadolinium-based contrast agents . The youngest reported affected pediatric patient is 8 years of age, and all reported pediatric patients had significant renal dysfunction. As there are no evidence-based guidelines for the prevention of NSF in children, we recommend that adult guidelines for identifying at-risk patients and administering gadolinium-based contrast media in the presence of impaired renal function be followed. While there has been no reported case of NSF in a very young child, caution should be used when administering these contrast agents to preterm neonates and infants  due to renal immaturity and potential glomerular filtration rates under 30 ml/min/1.73 m2

Secretin MRCP Procedure

Coronal T2-weighted fast, thick-section section, spin-echo MR sequences with no post-processing are used allowing for repeated breath-holds for a dynamic series. These images allow for direct visualization of the pancreatic duct in a few seconds. A negative oral contrast agent, such as superparamagnetic nanoparticles suspensions (ferumoxil oral suspension, e.g Lumirem, GastroMARK) is given 10 minutes before dynamic imaging. The negative oral contrast suppresses gastrointestinal overlap and prevents confusion between pancreatic fluid outflow and possible gastric emptying, i.e. nulls the fluid signal in the stomach and duodenum. Our institution has been using pineapple juice as a negative oral contrast agent, given at a dose of 3 cups (approximately 500-600 cc) 5-10 minutes before the imaging study. Pineapple juice is very inexpensive, easily available, and well accepted by most patients. Compared to certain commercially available superparamagnetic oral contrast agents, pineapple juice offers a more subtle shortening of T2 by our observation, therefore avoiding the susceptibility artifacts associated with these standard superparamagnetic contrast agents. The mechanism of pineapple juice to shorten T2 is due to its relatively high manganese concentration. There have been reports to administer blueberry juice as oral contrast in the past for the same mechanism, however, we use pineapple juice because of its easy availability. Our institution does not give an antiperistaltic drug to eliminate motion artifact, since each image acquistion takes only 3 seconds and motion artifact is not a big issue.

Next, the patient is placed in supine position for imaging. A set of images is acquired before secretin stimulation to allow for optimal positioning of the imaged section. After administration of IV secretin (dose of 1 clinical unit per kilogram body weight or dose stated on the specific secretin brand insert), image acquisition of the optimal section is repeated every 30 seconds. This dynamic procedure is conducted for 10 minutes. The delay between ingestion of the oral contrast and the acquisition of the secretin dynamic images is less than 5 minutes. The overall study time is approximately 15 minutes. It is assumed that once the pancreatic fluid reaches the duodenum its signal is not dramatically suppressed by the negative oral contrast agent. In fact, the density of the negative oral contrast agents is different from the density of the pancreatic fluid, thus, the two liquid phases may coexist without mixing. The pancreatic outflow after secretin stimulation in healthy subjects is in the range of 2-5 mL per minute, presumably low enough to allow the two liquid phases to coexist without mixing. The extent of pancreatic fluid secretion is then classified using the above duodenal filling scoring system.

MRI scan, safe on patients with implanted cardiac devices: study

Patients with implantable cardioverter defibrillator (ICD) and/or cardiac pacemakers should no longer worry going for MR imaging, for various medical conditions that they have: a study report

The study overruled following concerns: movement of device inside the body (due to MRI electromagnetic radiation/waves); device heating up, and affecting/burning tissues; device malfunctioning etc.!

 Defibrillators help to restore normal rhythm of the heart, during fibrillation of heart muscles; on the other, the battery-powered cardiac pacemaker, embed under skin provides normal heartbeat (timed electrical pulses) stimulating the muscle, during specific heart conditions.With specific procedures require to be followed – patients with newly implanted cardiac devices can definitely undergo MR imaging (securely), for cancer and other disorders/irregularities. (Courtesy: Johns Hopkins University)

For specific MRI procedures – pacemakers produced in 1999 (or later), and defibrillator in 2000 (or later), with cardiologist and other skilled professionals to program the device, to make it MRI-safe, and observe the heart rhythm during the scan, will do!

Of various patients (with implanted cardiac devices – either cardiac pacemaker or defibrillator) that were studied by, no significant issues were reported after they have had MRI done (except for less than 1% of subjects).

Researchers did both during MRI examination: turned the device off, and turned down the sensitivity of the equipment to electromagnetic fields; study authors found the device being set again (reset to default settings), and/but this did not cause harm to any of the patients with implanted cardiac devices that were scanned through.

No patient was required cardiac device replacement, as the devices were re-programmed after the process (MRI) was successfully done on all of them.

Experts say, during an MRI, the study required skilled nurse and Electro-physiologists to tackle any emergency, and due to extra resources required for it, not all care facilities would be able to manage the process (MR imaging) on patients with implanted cardiac devices.

Heart devices compatible with MRI (nowadays) are widely available from various manufacturers; stay tuned with MedicExchange for details about companies/vendors with MRI-safe cardiac devices, and other related!

Signal-to-noise ratio (SNR), imaging time, and resolution: Three factors of MRI image quality

Three factors of image quality, however, are well characterized: the signal-to-noise ratio (SNR), imaging time, and resolution. SNR is the ratio of the strength of the magnetism of precessing spins (MR image signal) relative to the random magnetic fields produced within the patient (noise). Resolution indicates the level of detail that can be seen in an image and is obtained by sampling wave patterns with a wavelength equal to the desired resolution distance (in all directions) as well as a complete set of waves that vary more slowly. The three quantities are related by the following equation:

SNR

a  (voxel size)*(imaging time)1/2

where the size of a voxel (short for volume element, the three-dimensional equivalent of a picture element, or pixel) is given by the product of the two in-plane resolutions multiplied by the slice thickness. For example, if an MR image is collected with in-plane resolution decreased from 1.0 mm2 to 0.5 mm2, SNR is reduced by a factor of four but can be restored by increasing imaging time sixteenfold.

The equation represents an unbreakable physical barrier. Technological barriers, however, lower the SNR from its optimal state for a given voxel size and imaging time and limit the minimum resolution and imaging time. These issues are addressed below, and some current and future solutions are considered.

Increasing SNR 

A high SNR for a fixed voxel size and imaging time can be obtained by increasing in vivo magnetization or the efficiency of detection. Magnetization can be increased by increasing the magnetic field B0 in which the patient is being scanned. The fraction of parallel, or detectable spins (roughly 10/million), is proportional to B0. Doubling the magnet strength of a scanner doubles this fraction and doubles the MR imaging signal to a first approximation. Higher manufacturing costs, patient safety, and other field strength-related phenomena are hindrances to using higher field strengths, but the simple notion that doubling the SNR can reduce scan time by a factor of four (from the above equation) for many scans is a powerful motivator.

The efficiency of detection can be increased by the proper choice of RF coils. Small coils are less noisy than large ones, but they can only detect signal from a limited area. Recent advances have led to phased array coils,[9] sets of coils that act independently but together measure signal from a wide area. Signal detection with a large set of small coils is typically less noisy than that obtained with one large coil. The drawback of phased array coils is the added hardware and computer power necessary to process multiple signals.

Imaging Time 

Imaging time is limited by how fast all the spatial waves in k-space necessary to complete an image with the desired resolution can be collected. These waves are produced by turning on the field gradients. Stronger field gradients can produce a greater variety of waves in a shorter amount of time than can weaker field gradients. To measure a two-dimensional set of waves, these gradients must be able to change direction rapidly so that the signal can be sampled over all of k-space. Thus, larger gradient amplitudes and gradients with higher slew rates (the rate at which the gradient can change direction) allow data to be collected more rapidly. Smarter sampling strategies (e.g., sampling trajectories through k-space) also help reduce imaging time. A recent advance is `real-time' MR imaging. Still in its infancy, this technique includes real-time tracking of interventional devices, interactive movement of the imaging plane, and monitoring the passage of a bolus of contrast agent.

At least two factors involving patient safety may ultimately impose lower limits on imaging time: the specific absorption rate (SAR) and field gradient-induced nerve stimulation. The first factor, SAR, relates to patients becoming heated from exposure to the RF pulses. The RF pulses stimulate charged matter to vibrate at the Larmor frequency and add thermal energy to the patient. Current guidelines from the Food and Drug Administration limit power deposition to an amount which, if the patient had absolutely no cooling mechanisms at all, would heat the patient about 1º C/hour. Consequently, the amount of RF that can be used to excite and refocus spins is limited. The second factor, nerve stimulation, occurs when the field gradients are switched too rapidly, inducing current flow in the affected nerves. Although many have experienced peripheral nerve stimulation, which is probably harmless, ventricular fibrillation must not be induced. Proper design of the coils that create field gradients can minimize, but not eliminate, this effect.

Resolution 

Other than limited SNR, which is a significant limitation to high-resolution MR images, other barriers are surmountable. Higher resolution scans require more computer memory and faster computer processing. A set of 128 slices, each producing a 512 x 512 pixel image and sampled from a four-element phased array coil set, requires about a gigabyte of memory. This is now possible but was less feasible just 5 years ago. Component stability, necessary for precise spatial encoding, is also improving through the use of shielded gradient coils, an innovation that is critical to obtaining advanced sequences such as EPI and spiral scanning.

Another barrier to improved resolution is physiologic motion from bulk motion, peristalsis, respiratory motion, and cardiac motion. The different time scales of these motions present different challenges for collecting data. Physiological motion can be circumvented in three ways. First, the motion can be monitored and the imaging data collected only during a quiescent period when tissues are assumed to return to the same state. Second, the motion can be monitored and corrected when the image is reconstructed. Finally, the image data can be collected fast enough to avoid the motion. The first scheme has been the basic way to obtain routine images in the abdomen, with the use of cardiac and respiratory gating. An effective application of the second scheme is the use of navigator echoes[2] in cardiac examinations to correct for respiratory motion. The third scheme is the most robust because motion can often be too unrepeatable and too complex for the first two schemes. Again, however, high-resolution scans collected in a brief time have a limited SNR.

Fat-saturated coronal postcontrast T1-weighted Pituitary gland

Fat-saturated coronal postcontrast T1-weighted magnetic resonance image is useful for assessing the pituitary gland for residual tumor or for a recurrence after surgery.

Image Contrast in MRI

Basic contrast in MR imaging relies on the differences in the density of water and fat, T1, and T2 of different tissues. The strongest signal is achieved with a long TR (allowing full spin realignment between excitations) and short TE (measuring the signal before significant T2 decay). Because the resulting image contrast is based mostly on the density of protons, such images are appropriately called proton density weighted (Fig. 5A). Beyond this, contrast is added only by making tissues darker. Adding image contrast based on differences in the T1 of tissues is achieved by reducing TR to a value about equal to the average T1 of the tissues of interest. Images with this modification are called T1-weighted images (Fig. 5B). This TR shortening preferentially darkens spins with longer T1 values, which do not recover as quickly as those with shorter T1 values. The addition of contrast based on differences in T2 is best achieved by measuring the MR image signal at a TE about equal to the average T2 of the tissues of interest, resulting in T2-weighted images

Figure 6.  Illustration of slice selection.  (A) Spins at rest are oriented vertically with the magnetic field.  A magnetic field gradient causes the magnetic field strength to be weaker on the left and stronger on the right so that the corresponding Larmor frequency is lower on the left and higher on the right.  Application of a radio frequency (RF) pulse excites a (B) plane of spins whose Larmor frequency falls within the frequency range of that RF pulse.

This increase in TE preferentially darkens spins with shorter T2 values, which decay more rapidly than those with longer T2 values. T1 and T2 contrasts are rarely combined because objects that remain bright on a T1-weighted image tend to be dark on a T2-weighted image and vice versa. Thus, the combination of these weightings would result in an image where all tissues are dark—some from insufficient T1 recovery of spin alignment with B0, others from T2 decay of the precessing magnetization.

Total Imaging Matrix(TIM) technology in MRI

Total Imaging Matrix(TIM) technology in MRI 
TIM is a Revolutionary new Advanced MRI System which is faster, quieter and wider, allowing the ultimate flexibility for coverage of the body in a much less confining environment. The new technology utilizes a Total Imaging Matrix, which allows scanning multiple parts of the body without interrupting the exam for equipment or patient repositioning. The spacious system allows many procedures to be performed feet first without requiring the patient to have their head inside the tunnel. As a result the whole MRI experience is significantly quieter and more comfortable especially for claustrophobic patients.

Non-Breathhold Liver MRI (TurboFLASH and HASTE)

Introduction

The main reasons for investigating the use of non-breathhold techniques is the fact that many patients are older and non-cooperative such that they cannot hold their breath for twenty seconds, the time required for most available breathhold techniques. Other reasons include patient debilitation, language barriers, and hearing disabilities, which prevent patients from understanding and performing proper breathhold techniques.

Non-breathhold techniques are based on single-shot sequences such as turbo fast low-angle shot (turboFLASH) and half-Fourier acquisition single shot turbo spin echo (HASTE) sequences. With the image acquisition duration of about one second, these sequences are rendered relatively breathing independent. Newer techniques for non-breath hold patients include respiration triggered sequences, such as, PACE 

Tips For Non-Breath Hold Patients

With proper coaching and instructions, most patients are able to hold their breath for longer than 20 seconds. The goal is to have patients perform a breath-hold for 20 seconds to acquire artifact-free images. The technologists should assess each patient's breath holding capacity as they are setting up the patient and coach them on instructions. Remember that some patients cannot do a breath-hold because they cannot understand or cannot hear the instructions. It is important to make use of family members and friends to translate or relay instructions to the patient if needed. Also, in patients with hearing impairments, the room lights can be used to signal breath-holding instructions to the patient.

All studies, except prostate and some pelvic studies are best done using a breath-hold technique. If the patient cannot hold their breath, most breath-hold sequences can be replaced by non-breath hold sequences. However, non-breath hold sequences usually are of inferior quality.

Before resorting to a single shot sequence, try the following steps:

1. Provide supplemental oxygen via a nasal cannula, especially if the patient seems to have borderline breath-holding capacity or is over the age of 70.
2. Shorten breath-hold without sacrificing too much resolution, e.g. a VIBE sequence with 6-7 mm section thickness is better than a turboFLASH sequence.
3. Try to run the normal sequences on inspiration.

Shorter acquisition times can be achieved by:

1. Decrease the number of slices on some 2D sequences, which allows you to decrease the TR.
2. Try parallel imaging, if available.
3. On 3D sequences, minimize slab thickness in order to reduce the number of partitions while maintaining a reasonable effective thickness.
4. Enlarge the FOV and increase the rectangular FOV. Note that resolution decreases in the read direction.
5. Try to use an alternative plane. The sagittal plane may allow better use of rectangular FOV.
6. Decrease the matrix size, i.e. the number of phase-encoding steps. Note that the resolution will decrease.

TurboFLASH Technique For T1-Weighted Imaging

Fast T1-weighted imaging can be accomplished with magnetization-prepared GRE sequences (e.g., TurboFLASH). A section-selective 180-degree inversion pulse is applied as part of this sequence, and then the data acquisition occurs during the T1 recovery of tissues following the inversion pulse. The inversion pulse provides flexible image contrast. When appropriate inversion time is selected, effective T1 contrast can be achieved for abdominal imaging. In such an approach, images are acquired sequentially, each slice requiring less than 1.5 seconds acquisition time. Using this technique, rapid T1-weighted images of the abdomen can be obtained in a single breath-hold. However, since the images are acquired sequentially with very fast acquisition time on a per-slice basis, this sequence can be used in patients with very limited breath-hold capacity. In and out-of-phase images can be obtained by the use of appropriate TE values so that two separate image sets can be acquired, one when fat and water are in phase and the other when fat and water are out of phase.

When performed with contrast administration, the timing of a triple phase turboFLASH acquisition should aim to achieve arterial, portal venous, and equilibrium phases. The arterial phase acquisition can be performed with a scan delay equal to the patient circulation time.

HASTE For T2-Weighted Imaging

Fast T2-weighted imaging can be performed using single shot turbo spin echo sequences such as HASTE. Typically, images are acquired in less than 1-1.5 seconds each. Note that because of the long echo train, T2-weighting is not as good with conventional spin echo or fast spin echo sequences. This is particularly important caveat in the setting of suspected hepatocellular carcinoma.

Helium in MRI systems

Most MRI systems use a superconducting magnet (in short term being called: MRI Magnet), which consists of many coils or windings of wire through which a current of electricity is passed, creating a magnetic field of up to 3.0 tesla. Maintaining such a large magnetic field requires a good deal of energy, which is accomplished by superconductivity, or reducing the resistance in the wires to almost zero.
To do this, the wires are continually bathed in liquid helium at 452.4 degrees below zero Fahrenheit (269.1 below zero degrees Celsius).
In order to reach and maintain such a low degree, the Magnet casing of MRI system and its cooling system must be filled by Helium (H2) in liquid form. Each MRI machine in avarage needs 1700 litters of liquid Helium and the Helium must be refilled from time to time. Usually mass density of liquid Helium is 1.25 Kg/L, Which approximately means an operational MRI system needs over 2 metric tons of liquid helium with 99.999% purity.

MR spectroscopy in Epilepsy MRI

A normal mesial temporal lobe showing high levels of choline presumably reflects a difference in the cellular composition between the allocortex and neocortex. Thus regional metabolic variations must be considered when pathologic conditions involving the mesial temporal lobe are evaluated. There is some evidence to suggest that the distribution of N-acetyl aspartate (NAA) in the hippocampal neurons is not uniform. Mouritzen found an increase in the number of cells from the anterior to the posterior in the pyramidal cells, whereas Babb et al., did not find statistically significant difference in the number of cells between the posterior and anterior sections. According to Vermathan et al., the anteroposterior difference could be due to fewer neurons in the anterior hippocampus compared with the posterior or due to increasing thickness from the posterior to the anterior leading to different contributions from adjacent tissue.

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Proton magnetic resonance spectroscopy (1H-MRS) has been used to assess metabolite abnormalities in the seizure focus, and the reduction of NAA is a typical finding a-c. In addition, metabolite changes can also be identified outside the seizure focus in patients with HS, reflecting a widespread disorder.MRS not only helps in the diagnosis but also in the prediction of antiepileptic drug response in patients with temporal lobe epilepsy


A patient with left mesial temporal sclerosis. High-resolution (HR) T2 coronal image (a) showing T2 prolongation and atrophy involving left hippocampal head. There is also evidence of collateral white matter atrophy on the left side. Proton spectroscopy metabolic map. (b) shows reduced NAA (N-acetyl aspartate) in left hippocampal head and body. Spectroscopy map (c) from a normal subject shows similar NAA on both sides. (d–f) A young female patient with temporal lobe epilepsy and right mesial temporal sclerosis. HR T2-weighted image. (d) showing signal changes involving right hippocampal head. Atrophy is appreciated in 3D SPGR. (e) Apparent diffusion coefficient. (f) in the right hippocampus is high, secondary to gliosis (arrow)

Dynamic contrast-enhanced (DCE)-MRI

Dynamic contrast-enhanced (DCE)-MRI is a technique whereby a standard low-molecular weight Gadolinium agent is administered intravenously at a standard rate, followed by sequential imaging of a region of interest (ROI) within the target lesion for up to 30 minutes. Signal intensity changes are measured within the ROI relative to normal tissue and plotted against time, allowing analysis of contrast "wash-in" and "wash out" components of the enhancement curve. Simple semi-quantitative analysis is performed by assessing the nature of such curves, an example being the evaluation of breast lesions. The slope of the wash-in and wash-out components of the curve, time to maximal enhancement or time to peak (TTP)] and area under the curve (AUC) provide semi-quantitative data that can be utilized to derive information on tumor blood flow, concentration, and tissue permeability.From these data, additional metrics such as mean transit time (MTT), a measure of the time taken for blood to perfuse a tissue, can be derived. Drawbacks of this method include the influence of protocol parameters such as contrast agent concentration, rate of injection, and variation in imaging hardware settings.
Alternatively, post-processing techniques based on kinetic modeling can be applied wherein a computer analyzes the contrast enhancement patterns on a pixel-by-pixel basis to derive quantitative measures of permeability . Parameters such as Ktrans (a measure of blood flow and permeability) and kep (the reverse flow constant) are obtained, thereby serving as markers of angiogenesis. DCE-MRI benefits from the widespread availability of MR, a lack of ionizing radiation, the transferability of protocols to existing scanners, and the use of standard gadolinium-based agents. Indeed, DCE-MRI has been studied in Phase II and III chemotherapeutic trials of anti-angiogenic agents and remains the most widely adopted imaging method for quantifying angiogenesis. However, DCE-MRI is not without its problems. The required post-processing and additional interpretation add to the reporting time; realistically an MR physicist needs to be on site, which is not possible in every center. In addition, the relationship of gadolinium concentration to signal intensity is not linear and depends on the T1 relaxivity of the tissue imaged - this can be partially overcome by the acquisition of a T1 map. Furthermore, there is disagreement on the optimal kinetic model to use and although the selection of an arterial input function should aid standardization, it often results in an additional variable. These problems mean that standardization is still an issue, making comparison between centers problematic.

Dynamic contrast-enhanced (DCE)-MRI enhancement curves

Dynamic contrast-enhanced (DCE)-MRI enhancement curves 

Dynamic contrast-enhanced (DCE)-MRI enhancement curves for normal tissue (red) and malignant tumor tissue (blue). TTP = time to peak enhancement within tissue; area under the curve (AUC) = shaded region. Wash-in and wash-out rates represent the velocity of enhancement and velocity of loss of enhancement, respectively, and together with AUC reflect underlying characteristics of tumor microvasculature that facilitate tumor classification and differentiation.

MRI LUNG PERFUSION

MRI pulmonary angiogram is a medical diagnostic test to obtain images of the pulmonary arteries.
On this healty individual:
the 3D reconstrution of the MRA image (1) allows the visualization of the entire pulmonary vasculature, identifying the subsegmental pulmonary arteries.
Dinamic contrast-enhanced MRA image in the oblique axial plane (2, 3, 4) allow the evaluation of pulmonary circulation, including perfusion of the lung fields,
which is homogeneous and symmetric.

MRI Spectroscopy Quality factors

Several effects can affect the quality of the processed spectra:

• Large residual fat signal can reduce the quality of the fit. The analysis range can be chosen such that fat is excluded.
• If residual fat is not present, increasing the analysis range can improve the quality of the baseline correction.
• Broader linewidth can cause the fit to fail if too many baseline polynomials are used. Improve by reducing the number of polynomials. Always check the quality of baseline correction in the spectral display.
• Lock relative frequency and/or lock relative width can be used if one or more peaks cannot be detected properly due to low signal.
• Lock relative frequency and/or lock relative width should not be used if fine control of the fitting is required. 

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Upper spectrum: Increased analysis range. Lwer spectrum: lock relative frequency is not used. The fit for choline and creatine is more accurate.