Sequestration
In cases of bronchopulmonary sequestration, parts of the pulmonary parenchyma may be found without or with an atypical connection to the tra-cheobronchial tree. Pulmonary sequestration may be classified as either extralobar or intralobar sequestration. Extralobar sequestration is usually located in the posterior costodiaphragmal recessus and is typically more left sided than right sided. Less frequently it is located in the upper abdomen or the mediastinum. In about 50 of cases, extralobar...
Accuracy of Renal MRA Techniques in Literature
Table 1 shows sensitivity and specificity data reported for diagnosing renal artery stenosis using non-contrast MR angiography. Many of the limitations due to flow and saturation artifacts on flow-based techniques are eliminated by using gadolinium contrast to enhance the renal MRA examina tion. Gadolinium contrast agents enormously increase the SNR allowing for higher resolution in short scan times. Using conventional angiography as a reference standard, the reported sensitivity and...
Portal Hypertension
DSA in patients with portal hypertension is often performed to measure portal venous pressures and the portal-systemic pressure gradient. These measurements can not be made directly using Fig. 2a-c. 44-year-old patient with hepatic cirrhosis and repeated gastrointestinal haemorrhage. Three rotated MIP displays of the portal venous phase 3D data set depict the portal venous morphology to good advantage. The splenic vein is dilated and is draining into a convolute of gastroesophageal collaterals...
Patient Preparation
As with any MR scan, proper patient preparation will minimize exam duration and improve clinical Fig. 3. Vascular Image Contrast on CE MRA. On CE MRA, the repetitive application of radiofrequency pulses generates the necessary image contrast to distinguish Gd-enhanced blood from unenhanced structures. Proper timing of imaging to occur during the phase of preferential arterial enhancement will thus result in the selective visualization of Gd-enhanced arteries over adjacent un-enhanced veins and...
Tricks
Korosec et al 2 described yet another method for time-resolved 3D MRA called TRICKS Time-Re solved Imaging with Contrast Kinetics . TRICKS is, however, vastly different than sub-second 3D MRA. The TRICKS algorithm consists of an alternative temporal k-space sampling scheme that repetitively samples low and high spatial frequency k-space views in a interleaved and slightly asymmetric fashion Fig. 5 . The low spatial frequency data i.e. central k-space data is updated at a much faster rate i.e....
Celiac Pseudostenosis
Extrinsic compression of the celiac axis by the median arcuate ligament can simulate a celiac axis stenosis. Often this has a characteristic appearance in which the celiac axis is pulled inferiorly. This extrinsic compression varies with respiration, and thus may appear more or less severe, depending on the patient's degree of inspiration or expiration. Although usually asymptomatic, there have been reports of relief of abdominal symptoms following surgical release of a severe extrinsic...
Hypogenetic Lung Syndrome Scimitar Syndrome
In scimitar syndrome one lung is hypoplastic and drained by an anomalous pulmonary vein. The feeding pulmonary artery might be hypoplastic or atretic with systemic collaterals. Abnormal bronchial branching or bronchial hypoplasia in coexistance with abnormal pulmonary segmentation might occur. It is located predominantly on the right and is associated with congenital heart disease in approximately 25 of the patients. Most commonly the atrial septum is involved 22 . If the scimitar vessel drains...
Renal Vascular Malformation
Renal arteriovenous malformations AVMs and fistulae are abnormal communications between the intrarenal arterial and venous systems. Renal AVMs are usually identified during the evaluation of gross hematuria. Two types of congenital renal AVMs are described, including cirsoid AVM and cavernous congenital AVM which is the less common type. Acquired AVM or fistula can occur following trauma, especially from renal biopsy. An-giographic embolization is the preferred treatment for symptomatic AVMs....
ContrastEnhanced MRA
With the introduction of CE-MRA, it became feasible to generate high-quality images of the mesen-teric vasculature 14-16 . Imaging in the coronal plane permits evaluation of the aorta, splanchnic arteries and portal vein in one examination. A partition thickness of 3 or 4 mm or even 5 mm is acceptable if zero padding is available for interpolation. In the absence of an interpolation algorithm, the slice thickness should be kept to less than 3 mm. To determine stenotic disease of the proximal...
Coronary Vessel Wall Imaging using MRI
Imaging of the coronary artery vessel wall is probably the most challenging task in cardiac MRI because of the small dimension and constant motion of the coronary arteries. Simultaneously, the need for high contrast between the coronary lumen blood pool and the surrounding coronary vessel wall is mandatory. However, this is very similar to the challenges faced by coronary MRA in general. The first successful implementation of coronary vessel wall imaging in humans involved the use of a...
Normal Anatomy Figs 1 2
The abdominal aorta bifurcates at L4 level into the common iliac arteries. The common iliac artery bifurcates into internal iliac and external iliac arteries in front of the sacro-iliac joints at the level of L5 S1. The internal iliac artery travels inferiorly towards the sciatic foramen and divides into the anterior trunk which supplies via numerous named arteries the pelvic viscera and the posterior trunk which supplies the muscles of the lateral pelvis . The external iliac artery becomes the...
Contrast Administration
CE MRA has traditionally been performed using one of the commercially available extracellular Gd-chelate contrast agents. The rate of injection affects the peak Gd concentration and thus the achievable arterial SNR. Generally, a faster injection rate will result in higher arterial SNR, but shorter bolus duration and earlier venous enhancement. Injection rates of 2 mL sec are ideal for most CE MRA applications, with little benefit shown for higher rates 63 . Slower injection rates result in...
Receiver Bandwidth
Receiver bandwidth is another pulse sequence parameter. As with other applications, higher SNR can be achieved with narrower bandwidth, but generally at the expense of scan time. SNR is inversely related to the square root of the receiver bandwidth. Thus, a doubling of the receiver bandwidth results in a reduction of the SNR by the square root of 2. In patients with reduced breath holding capacity, a wider bandwidth e.g. increase in kHz on a General Electric MR scanner less water fat shift on a...
Pulmonary MRA
Time resolved imaging can be useful for optimization of a pulmonary 3D CE MRA. Pulmonary 3D CE MRA has become particularly popular for pre-procedural pulmonary venous mapping in patients with paroxysmal atrial tachycardias in whom electrophysiological pulmonary venous ablation procedures are contemplated. In this case, time resolved imaging can be used as a bolus timing scan to ensure proper timing of imaging for peak pulmonary venous imaging. This can be performed using a fast 2D or 3D...
Paramagnetic Contrast Agents Blood Pool Contrast Agents
The so-called paramagnetic blood pool contrast agents are agents for which the intra-vascular residence time is considerably extended compared to the conventional first pass only gadolinium agents. With these agents the intravascular signal remains high for an extended period of time thereby permitting MR imaging during a more prolonged steady-state timeframe in addition to conventional first pass CE-MRA. There are two principal types of paramagnetic blood pool contrast agent those whose...
Normal Variants
Aberrant or accessory renal arteries may arise off the aorta or iliac arteries. They are present in up to 25 of patients, originating above or below the main renal artery Fig. 2a, b . Accessory renal arteries will be seen coursing into the renal hilum usually perfusing the upper or lower polar regions. If an aberrant artery enters the upper or lower pole directly, without passing through the renal hilum, it is called a polar artery Fig. 3 . These aberrant Fig. 2a, b. Renal MRA with single dose...
Surface Rendering
Surface rendering Fig. 6 uses the boundary voxels between the object to be displayed and the background to create a 3D surface. Hence, it requires preliminary segmentation. Accurate segmentation methods capable of precisely delineating the vascular structures and of separating them from other tissues are still being developed. However, for an approximate visualization, segmentation may be achieved by simple thresholding. In surface rendering, the voxels located at the edge of a structure are...
Clinical Indications 1
The clinical presentation of pulmonary embolism PE mimics many other common and uncommon diseases. If not quickly and correctly diagnosed PE carries significant morbidity and mortality, especially in the hospitalized patient. The mortality rate for PE is less than 8 when the condition is quickly diagnosed and treated correctly but approximately 30 when untreated 11 . For this reason an accurate screening test for the detection of PE is very important. Strategies for the accurate evaluation of...
NonContrastEnhanced Renal MRA
Many renal MR angiography techniques have been described. Standard non-contrast, flow sensitive sequences include time-of-flight TOF and phase contrast PC MRA. The image quality of these flow-based techniques is limited by diminished flow in patients with vascular stenosis or parenchymal disease and by motion artifacts due to respiration during acquisition times that are too long for breath-holding. Proximal stenoses where there is less respiratory motion are better depicted than distal disease...
Renovascular vs Parenchymal Renal Disease Quantitative Perfusion Imaging
Renal artery stenosis comprises only one entity in a large complex of overlapping diseases that ranges from essential hypertension to primary parenchymal disease. A high incidence of coexisting renoparenchymal disease explains why many patients do not improve after revascularization. Parenchymal disease is a result of both primary causes such as diabetes or glomerulonephritis as well as secondary causes resulting from long standing renal artery stenosis. Recently, the possibility to perform...
Kspace Options
Another important concept concerning imaging parameters is the k-space acquisition order Fig. 8 7,8,12-14,48-51 . As with all MR acquisitions, the resulting image contrast is dominated by data within the center of k-space also called low spatial frequency data Fig. 9 . Traditional k-space acquisition schemes are linear in that k-space data is acquired sequentially one line at a time from top to bottom Fig. 10 . The central k-space data are thus typically acquired during the middle of any given...
Renal Arteries
Renovascular hypertension and ischemic nephro-pathy have become topics of interest to all en-dovascular specialists with the increasing use of endovascular stent technology to treat these conditions. A study designed to visualize the renal ar- Fig. 7. Abdominal MRA shows left renal artery stenosis arrow in a patient with severe aortoiliac disease Fig. 7. Abdominal MRA shows left renal artery stenosis arrow in a patient with severe aortoiliac disease Fig. 8. Abdominal MRA shows bilateral renal...
Symmetry of Renal Length and Parenchymal Thickness
Normal kidneys measure 11-13 cm in length with a tendency for the right kidney to be slightly smaller up to 1 cm compared to the left. Typical parenchymal thickness is 1.7 0.3 cm 29 . Parenchymal volume is a more accurate parame Fig. 19a-e. Asymmetric kidney size and function due to severe renal artery stenosis a-d . Also note spin de-phasing on 3D phase contrast at and just distal to the renal artery stenosis arrowin e Fig. 19a-e. Asymmetric kidney size and function due to severe renal artery...
References Mud
1. Meaney JF et al 1997 , Diagnosis of pulmonary embolism with magnetic resonance angiography. N Engl J Med 336 20 1422-7 2. Goyen M et al 2001 Dynamic 3D MR angiography of the pulmonary arteries in under four seconds. J Magn Reson Imaging 13 3 372-7 3. Finn JP et al 2002 Thorax low-dose contrast-enhanced three-dimensional MR angiography with subsecond temporal resolution-initial results. Radiology 224 3 896-904 4. Hatabu H et al 1996 Pulmonary perfusion and angiography evaluation with...
Technique
The typical cervical MRA examination should encompass the top of the aortic arch, inferiorly, and the skull base, superiorly. The extracranial course of both carotid and both vertebral arteries should be included in this field-of-view FOV . The radio frequency RF imaging coil should ensure adequate visualization of this large area of coverage while still maintaining a high signal-to-noise SNR ratio, which is required for proper visualization of vessel detail. Dedicated phased array...
Postoperative Surveillance
MRA has great usefulness in the post procedure monitoring of patients who have undergone en-dovascular repair of abdominal aortic aneurysm Fig. 3a, b. Normal post-operative MRA in two patients with different endovascu-lar stent grafts for AAA repair Fig. 3a, b. Normal post-operative MRA in two patients with different endovascu-lar stent grafts for AAA repair Fig. 4a, b. Post-operative CTA a and MRA b of same patient shows an endoleak that is only seen on MRA arrow Fig. 4a, b. Post-operative CTA...
Coils
High quality pedal MRA, like MR of any small region, requires an appropriately sized birdcage or surface phased array coil. For cases of targeted pedal only MRA, most investigators use a birdcage Fig. 3. Lateral DSA. AT anterior tibial artery, PT posterior tibial artery, Per peroneal artery, MT medial tarsal artery, LT lateral tarsal artery, AA arcuate artery, DP dorsalis pedis artery, Perf perforating artery, PA plantar arch, LP lateral plantar artery, MP Medial plantar artery, 1st DM first...
D Mr Dsa
With further refinements, namely a good mask subtraction, fast 2D pulse sequences can also be used to provide 2D projectional angiograms similar to those of conventional x-ray digital subtraction angiography DSA . Wang et al 5,6 have successfully implemented 2D MR DSA using a specialized off-line complex subtraction algorithm. This technique is particularly helpful for illustration of distal run-off vessels 6,7 .A series of relatively thick 8-10 cm 2D projectional images are acquired during the...
Phase Contrast Technique
Similar to magnitude contrast, phase contrast an-giography is based on the acquisition of two datasets that differ in the phase of moving spins 9,10 .At first, a flow-rephased sequence S is applied which defines the phase of transverse magnetization under conditions of total flow compensation. The second measurement S2 is flow-sensitive, utilizing special flow-encoding gradients to provoke a measurable phase shift. Contrary to the magnitude contrast technique, the chosen gradient is weak enough...
Paramagnetic Contrast Agents First Pass Gadolinium Agents
Currently, seven gadolinium contrast agents are approved in one or more countries of the world and an eighth is in the final stages of the approval process Fig. 2 . Although all are suitable for use in first-pass CE-MRA, few agents are actually approved specifically for this indication. Six of these seven agents possess no capacity for interaction with serum proteins and can be considered conventional first generation gadolinium chelates Fig. 1, column 1 Fig. 2a-f . The seventh agent,...
Clinical Applications 1
Indications for MR imaging of the central thoracic veins include the investigation of superior vena cava syndrome, assessment of mediastinal abnor Fig. 5a-d. Indirect contrast-enhanced MR venography of the central thoracic veins. Imaging was performed following the administration of 0.3 mmol kg paramagnetic contrast agent in the right antecubital vein. 3D data sets were acquired a in the arterial and b venous phase. A high grade stenosis arrows of the superior vena cava is best depicted on the...
r
Fig. 28a-c. Fusiform ectasia arrow of the supraclinoid internal carotid artery with involvment of the middle and anterior cerebral artery. The 3D TOF MRA a reveals fusiform ectasia of the internal carotid artery and its bifurcation. The CE MRA image b shows reduced saturation effect and better delineation of the malformation, and allows 3D reconstruction c Fig. 29a-d. Acute subarchnoid hemorrhage arrow at CT a . The 3D TOF MRA image b reveals a small aneurysm arrow of the internal carotid...
Indications for MRA
There is currently no agreement on use of MRA for patients with PAOD. However, because MRA delivers similar information to DSA, without the associated risks of iodinated contrast material 10, 11 or arterial catheterization 5-7 it is appropriate to consider MRA in ANY patient referred for catheter arteriography, however, some patients deemed to be at high risk of complications of conventional arteriography may be particularly suited to assessment with MRA 12 . Table 2 lists the patients that may...
Inflowrelated Signal Enhancement Inflow Effect
Although the signal of blood flowing quickly out of the measured slice is reduced with SE sequences, under certain circumstances the opposite effect may occur spins flowing into the slice may generate a higher signal than the surrounding tissue. This effect is referred to as inflow enhancement. On T1-weighted imaging, contrast is generated by repeated RF pulses that are applied with a time interval repetition time, TR that is shorter than the T1 relaxation time of the tissue typically TR lt 700...
I li
Fig. 25a-e. Superior sagittal and right transverse sinus thrombosis. 52-year-old female with seizures. T1-weighted MR images reveal isointense signal of the right transverse sinus a arrow and superior sagittal sinus b arrow . The T2-weighted c image reveals hyperin-tensity of the superior sagittal sinus arrow and the presence of small bilateral cortical infarction. The 3D PC MRA images d, e show the presence of thrombosis of the central and anterior portions of the superior sagittal sinus...
Clinical Examples 1
MRI permits an excellent workup of the anatomic and physiologic status particularly as regards congenital cardiovascular malformations of the aorta. Since children or young adults most frequently require evaluation, the lack of ionizing radiation and the excellent safety profile of the applied MR contrast agents are a considerable advantage when compared with other diagnostic modalities. Moreover, since patients with congenital cardiovascular malformations need regular follow-up, it is...
Patient Preparation Uch
It is important to first evaluate the patient's ability to hold his or her breath. The patient's breath-hold capacity dictates MRA scan duration, which should be prescribed to be short enough to enable patient compliance and successful breath-holding. Scan parameters should then be adjusted for the highest possible spatial resolution for sufficient anatomic coverage of the aorta, iliac and renal arteries back to at least mid-kidney. Patients who have a respiratory rate of less than 20 breaths...
Introduction Vsr
Contrast-enhanced magnetic resonance angiography CE MRA has become a routine procedure for the non-invasive visualization of vessels in most radiology departments. Unlike older MRA techniques i.e., phase contrast PC MRA and time-offlight TOF MRA , CE MRA does not suffer from artifacts caused by turbulence and in-plane saturation. This usually makes CE MRA easier to interpret than PC MRA and TOF MRA. Also, the lack of in-plane saturation in CE MRA permits imaging in the coronal plane, allowing...
Zero Filled Interpolation
Zero filled interpolation also known as sinc interpolation, zero padding or filling, overcontiguous and ZIP , is an image reconstruction algorithm in Fig. 12a, b. Ringing artifact on breath hold 3D renal CE-MRA in a 36-year-old man with left renal artery stenosis. This artifact is recognized by the presence of bright and dark lines a, coronal MIP b, coronal source image that parallel the edge of the enhancing abdominal aorta smallarrows and results from the premature acquisition of low spatial...
Clinical Applications Multistation MRA
With the development of moving or stepped table techniques, multi-station MRA has become a clinical staple for the evaluation of the peripheral runoff vessels 12-17 . The stepping table technique, akin to that used for peripheral x-ray angiography, consists of the progressive movement of the imaging field of view in conjunction with the arterial transit of a Gd-chelate contrast bolus down the lower extremities. This technique also called bolus chasing has become a clinical standard for...
Abdominal Aortic Aneurysms
Abdominal aortic aneurysms AAA occur in 57 of the population older than 60 years of age. Although most patients with AAA are asymptomatic, they can present with symptoms of mass effect, compression of abdominal organs, or visceral or peripheral emboli originating from the wall of the aneurysm. Rarely, patients present with back pain, which can represent rupture of the aneurysm, a surgical emergency. Patients older than 60 years of age who smoke and who are known to have atherosclerosis,...
High Field 3T Coronary MRA
Currently, the vast majority of research into coronary MRA as well as most technical innovations and clinical applications are performed on 1.5T systems. For many of these applications, limited SNR or lengthy examination times are impediments. The recent availability of high field systems 3T equipped with dedicated cardiac hardware real-time spectrometer, parallel receiver technology with high bandwidth, body RF send coil, vector ECG, etc. and software SENSE, navigators, interactive interface,...
Renal Artery Anatomy
Normally, each kidney is supplied by a single renal artery originating from the side of the aorta, immediately below the superior mesenteric artery typically at the level of L2 Fig. 1 . Each renal ar Fig. 1. Normal Anatomy A Coeliac trunc B Superior mesenteric artery C Right renal artery D Left renal artery E Inferior mesenteric artery f Lumbar arteries Fig. 1. Normal Anatomy A Coeliac trunc B Superior mesenteric artery C Right renal artery D Left renal artery E Inferior mesenteric artery f...
Embolization Procedures
Embolization has recently emerged as a first line therapeutic option for the treatment for several complex vascular lesions including peripheral aneurysms, arteriovenous malformations, and en-doleaks. The use of MRA for treatment planning and post-procedure follow up has been previously reported for a variety of specific conditions including intracranial aneurysms, pulmonary AVMs, and peripheral AVMs 16-18 . The one prerequisite is the use of MRI compatible embolic material. Platinum...
Imaging Technique
The sequences used for 3D CE MRA are spoiled gradient-recalled-echo SGE sequences with zero interpolation in the partition or the slice-selected direction. The abdominal aorta is generally well displayed with a contrast dose of 0.1 mmol kg of gadobenate dimeglumine Gd-BOPTA or 0.2 mmol kg of a non-protein interacting gadolinium Fig. 1. Schematic drawing of the normal anatomy of the abdominal aorta A Celiac artery B Superior mesenteric artery C Inferior mesenteric artery D Common iliac arteries...
Imaging of Extraanatomic Bypasses
CE MRA also appears useful for surveillance of extra-anatomic bypass grafts. These grafts are typi- Fig. 8. MR angiogram of a 37-year old patient with Takayasu disease and stenosis of the right common carotid artery arrow , occlusion of the left carotid and brachiocephalic arteries arrow and stenosis of the right renal artery asterisk Fig. 8. MR angiogram of a 37-year old patient with Takayasu disease and stenosis of the right common carotid artery arrow , occlusion of the left carotid and...
Liver Transplantation
Imaging proof of a patent portal vein is required for a patient to be placed on the liver transplant waiting list. Ultrasound can image the portal vein but is not 100 reliable. When ultrasound fails to adequately visualize the portal vein, 3D CE MRA offers a safe, accurate, and comprehensive assessment of portal venous anatomy without requiring iodinated contrast 16,17 . 3D CE MRA also evaluates the splenic vein, superior mesenteric vein SMV , inferior mesenteric vein, IVC and potential varices...
References Xbm
1. Hagspiel KD, Leung DA, Angle JF et al 2002 MR angiography of the mesenteric vasculature. Radiol Clin North Am 40 867-886 2. Baden JG, Racy DJ, Grist TM 1999 Contrast-enhanced three-dimensional magnetic resonance angiography of the mesenteric vasculature. J Magn Re-son Imaging 10 369-375 3. Meaney JF 1999 Non-invasive evaluation of the visceral arteries with magnetic resonance angiography. Eur Radiol 9 1267-1276 4. Vosshenrich R, Fischer U 2002 Contrast-enhanced MR angiography of abdominal...
Tumor Encasement
Tumors may enhance rapidly during the arterial phase, or, if hypovascular, the tumor may blend in with surrounding tissues making it difficult to identify. Retroperitoneal masses, and particularly pancreatic adenocarcinoma, may surround, encase, and narrow or even occlude the splanchnic arteries and portal venous system. Masses arising in the head of the pancreas tend to encase the SMA, SMV, and portal vein. Lesions in the body and tail of the pancreas tend to narrow the splenic vein. The...
Normal Anatomy Yag
The mesenteric venous anatomy Fig. 1 parallels the arterial distribution see VI.3 3-4 . The portal vein is formed by the splenic and superior mesen-teric veins. The pancreatic, left gastroepiploic, short gastric, and inferior mesenteric veins and splenic vein branches drain into the main splenic vein. The inferior mesenteric vein receives its supply from the left colic, sigmoid and superior hem-orrhoidal veins. It usually joins the splenic vein prior to the junction of the splenic vein with the...