By Dr Ranjith

1. CT , MRI &
ARTERIOGRAPHY
IN VASCULAR
SURGERY
Dr Ranjith kumar A

2. History
■ 1930s - Dutch radiologist Ziedses des Plantes first devised a technique that
reduced the problem of superimposition of structures in basic radiography (x-ray
tube and plain film)
■ Technique was called “planigraphy” or “tomography,” derived from the Greek
words tomos , which means “a section” or “a cutting,” and graphein, meaning
“to write.”
■ 1970s computational reconstruction of images, led to the development of
computed axial tomography (CAT scan, or later CT scan).

3. History
■ Two similar methods for transverse axial scanning and image reconstruction
were independently invented by Sir Godfrey Newbold Hounsfield in Hayes,
United Kingdom, at Elector-Musical Instruments (EMI) Limited Central Research
Laboratories, and Allan McLeod Cormack of Tufts University in Massachusetts
■ The first EMI scanner was installed in Atkinson Morley’s Hospital, Wimbledon,
England, in 1971. In the United States, the first installation was at the Mayo
Clinic in Rochester, Minnesota.
■ Hounsfield and Cormack shared the Nobel Prize in 1980.

4. Basic Principles
• The fundamental unit for this scanning method consists of an emitter and a
detector; an x-ray beam is transmitted through the tissue and detected on the
other side.
• The emitter produces a thin (highly collimated) x-ray beam that sweeps in linear
fashion across the body cross-section.
• The detector moves as a unit with the emitter and records data from 160
separate, parallel, and immediately adjacent beams.
• The emitter and detector units are mounted within a gantry, which is rotated 1
degree before another linear, transverse sweep takes place.
• This process is repeated through 180 degrees of rotation to produce the data
necessary to form a 160 x160 matrix for a single cross-sectional image.

5. Basic Principles
• Attenuation (the rate of reduction of x-ray energy recorded at the detector) of
multiple x-ray beams traversing the same point in the matrix from different
angles is collected and an ingenious method applied to calculate backward to
the density or CT number that must be present at each location in the matrix.
• CT number is said to be expressed in Hounsfield units (H).
• Clinically, CT numbers range from the extremes of air (− 1000 H) to dense bone
(> 1000 H), but fat (− 20 to − 100 H), water (0 H), and muscle and blood (40 to
60 H) tend to lie in a much narrower range.
• Differences in factors such as the energy level of the beam and tissue
thickness prevent the density in Hounsfield units from being absolutely
uniform from one CT scan to another, but the ranges are similar.

6. Principle of operation of a first-generation CT
scanner
Principle of operation of a third-generation CT
scanner

7. Types of Scanners
Single-Slice Sequential CT
 A first-generation CT scanner is capable of producing a cross-sectional image
with a 160 x 160 matrix.
 Applicable only to parts of the body with limited motion (e.g., the head)
because the back-calculation algorithm depends on the subject’s remaining in
one position while data are collected for the entire cross-section.
 Second-generation CT scan - used an emitter that produced a broader fan-
shaped x-ray beam and an array of 30 detectors instead of a single detector
 The time for a single cross-sectional scan was reduced to approximately 15
seconds

8. Types of Scanners
Single-Slice Sequential CT
• Third generation scanner - the emitter produces a wider fan-shaped x-ray beam,
and hundreds of detectors are arranged in an arc. Emitter and detector array
rotate in a continuous 180- or 360-degree arc to produce a complete cross-
sectional scan in 1 second
• Fourth-generation CT scanner, the detector array covers the entire 360-degree
arc and only the emitter rotates

9. Spiral (Helical) CT
• The slip-ring gantry, the emitter and detector array can rotate continuously in the
same direction, and at the same time, the computer can acquire data
continuously.
• The emitter traces out a spiral relative to the patient, which is referred to as a
spiral CT or helical CT scan

10. Spiral (Helical) CT
 A spiral CT scan collects data over a continuous
volume rather than discontinuous slices .
 Advantage of acquiring data over a continuous
volume is that thin axial slices can be
reconstructed from the digital data set at arbitrarily
small intervals without additional radiation
exposure.

11. Multislice (Multidetector) CT
• Multidetector scanners have multiple rows of detectors, volume to be scanned
can be covered more quickly
• A first-generation CT scanner produced a cross-sectional image with a 160x160
matrix, but current scanners typically generate a 512x512 matrix.
• Data points are displayed as a two dimensional (2D) picture, and each point in
the display matrix is a pixel (picture element).
• Data points are acquired in three dimensions, however, and each data point in
the matrix actually represents a voxel (volume element).
• Size of the voxel is determined by multiple factors, including detector design,
FOV (x, y direction), and thickness of the x-ray beam (z direction)

12. Spiral CT data are acquired and
stored over a continuous volume,
they can be used to create axial
(A), coronal(B), and sagittal (C)
sections.

13. Multislice (Multidetector) CT
■ One current advantage of CT over magnetic resonance imaging (MRI) is that CT
is typically displayed in a 512 x 512 or greater matrix, with resolution of 0.2 to
1 mm2 for each pixel. MRI is generally limited to a 256 x 256 matrix, and
resolution in the axial plane is roughly half that of CT.

14. CT Angiography
■ Visualization of vessels on CT is limited by the similar densities of blood and soft
tissue.
■ Optimal visualization of the vessels (computed tomographic angiography [CTA)
was not possible until the availability of spiral CT
■ Advantage of spiral CT over sequential CT is the possibility of imaging a larger
part of the body in a shorter time.
■ Timing of the initiation of image acquisition relative to injection of the
contrast agent is crucial for maximizing opacification of vessels in the scanned
volume

15. CT Angiography
■ CTA generally requires a significant infusion of contrast material.
■ In the past, a typical CTA study from the celiac axis down to the external iliac
arteries would require 120 to 180 mL of nonionic contrast.
■ Optimization of scanning and power injector protocols and the use of saline
push bolus techniques reduced this volume significantly, and often volumes do
not exceed 100 mL.

16. CT Angiography
■ Split-bolus techniques are alternative ways of administering intravenous
contrast.
■ These techniques employ multiple phases, for instance, enhancement of
venous and arterial structures, in one single scan.
■ One early bolus of contrast and one late bolus of contrast administration before
obtaining the CT scan.

17. Dynamic CT Scanning
■ Basic concept is that of obtaining CT images at a fixed location (in other words,
without moving the table) during the injection of contrast material.
■ After injection of a contrast agent, imaging at a fixed position with continuous
rotation of the CT gantry will provide insight into passage of contrast material
through the arterial, capillary, and venous phases, representing tissue perfusion.
■ Currently used predominantly for brain and cardiac perfusion studies

18. Postprocessing
Multiplanar Reformatting
■ Reformatting CT data into coronal, sagittal, or other nonaxial planes is often
referred to as multiplanar reformatting or multiplanar reconstruction (MPR)
■ The ability of spiral CT to view the data in coronal, sagittal, or arbitrarily
defined planes often gives more insight into vascular anatomy than possible
with axial views alone

19. Measurements
■ Simple axial CT slices often do not cut through planes perpendicular to the
vessel, which results in elliptical cross sections that can make measurements of
diameter difficult .
■ Narrowest diameter of the elliptical cross-section is the “true” arterial diameter,
■ Not always the case because the aorta does not always have a simple
cylindrical or conical shape
■ Conventional CT may lead to a slight overestimation of diameter on axial
slices, whereas spiral CT slices reconstructed perpendicular to the vessel tend
to be more accurate

20. Measurements
■ Spiral CT with 3D reconstruction and CT reformats perpendicular to the
vessel lumen eliminate the diameter measurement problems associated with
the other techniques
■ 3D reconstructions can be used to calculate the volume of any structure in the
3D model
■ Volume measurements are much more sensitive to changes in size than
measurements of maximal diameter
■ Volume measurements are much more sensitive than maximum diameter
measurements for the detection of changes in size of abdominal aortic
aneurysms (AAAs) after endovascular AAA repair

21. Three-Dimensional Reconstruction
■ For vascular structures, CTA produces contrast density within the vessel lumen
so that 3D reconstruction of the vessel lumen can be performed.
■ The density (CT numbers) of vascular contrast and bone may overlap. Bone
structures are either included in the model or “cut away” with a tool sometimes
referred to as an electronic scalpel
■ Calcium within the vessel wall cannot be cut away easily, however, and is
usually included in a reconstruction of the contrast-enhanced vessel lumen.

22. Optimization of Acquisition
■ The best image quality is obtained with a pitch (the ratio of table speed to slice
thickness) of 1 (e.g., 3-mm/sec table speed and 3-mm collimation), but this limits
the distance that can be covered.
■ With the use of 180-degree linear interpolation algorithms instead of the original
360-degree ones, images of good quality can still be obtained with a pitch
greater than 1

23. CLINICAL APPLICATION
The most common noncardiac, nonbrain vascular imaging indications for CTA are
– Aortic disease (aneurysm, dissection, trauma)
– Peripheral arterial occlusive disease
– Renovascular disease
– Venous disease
– Vascular malformations.

24. Aortic Disease
■ Primary imaging modality for aortic disease.
■ Excellent spatial resolution with 3D image reconstruction allow for highly
accurate measurements of aortic aneurysms in the preoperative planning
of endovascular repair, as well as postoperative follow-up.
■ Allows for imaging of small branches such as the intercostal arteries
(important for prevention of spinal cord infarction during thoracic aortic repair)
■ And for tiny contrast enhancements in thrombus (important for identification of
endoleak).
■ The CTA acquisition speed of the entire aorta (currently, within 1 minute; in
newer scanners, within a few seconds) allows accurate imaging of the aorta in
acute cases such as ruptured aneurysm, aortic dissection, and trauma.

25. Aortic Disease
■ Endovascular repair of these acute diseases currently relies on acute CTA
■ Important advantage of CTA over MRA in both the acute and elective setting is
the ability of CTA to image calcium, for instance, in aortic landing zones of
endovascular devices that depend on penetrating hooks and barbs or access
arteries that may render endovascular repair difficult or impossible
■ CTA is preferred over MRA when endovascular devices are in place because
metal artifacts are rarely a problem

26. Peripheral Arterial Occlusive Disease
■ Used to image the arterial tree from the aorta through the pedal vessels in a
single contrast-enhanced acquisition run
■ The high resolution of CTA allows for accurate delineation of stenotic
segments and planning for open and endovascular intervention.
■ Downside, interpretation of CTA images and reconstructions of small arteries
(tibial vessels) can be very tedious, particularly the distinction between calcium
and contrast
■ Overestimation of the severity of a calcified stenosis is common
■ Help differentiate occlusion from high-grade stenosis, and it provides better
anatomic reference than duplex

27. Peripheral Arterial Occlusive Disease
■ CTA also provides the option of adjacent imaging of the aortic arch and
intracranial arteries, which may be of help in the diagnosis and treatment of
neurovascular disease.
■ CTA can also often be used for diagnosis of mesenteric artery stenosis and
aneurysms and for preinterventional planning.

28. Renovascular Disease
■ CTA and MRA are comparable in sensitivity for the detection of proximal renal
artery stenosis.
■ If evaluation of more peripheral abnormalities is needed, MRA suffers
significantly from respiratory movement of the kidney.
■ The main benefit of MR for renal artery imaging is the fact that contrast-induced
renal nephropathy is avoided, although a limiting factor NSF due to gadolinium
in patients with renal failure.
■ Valid alternatives include time of flight or comparable MR techniques that allow
for flow imaging without the use of gadolinium; however, these techniques
provide less optimal imaging quality

29. Venous Disease
■ CT is an excellent modality to evaluate a variety of venous pathologies (proper
injection protocol with sufficient delay is chosen) , including mesenteric venous
thrombosis.
■ For the evaluation and detection of pulmonary emboli, CT has replaced lung
perfusion and ventilation studies.
■ For peripheral evaluation of venous disease (in legs, iliac veins, subclavian
veins), the optimal imaging modality is still duplex ultrasound because this also
provides essential flow information.

30. Vascular Malformations
■ The role of CTA in the evaluation of vascular malformations is limited.
■ Only in cases of high-flow malformations (AVM, AVF) can CTA support a proper
diagnosis; the extent and composition of the nidus cannot be adequately
evaluated .
■ For low-flow malformations there is virtually no role for CT imaging. The limited
soft tissue contrast and the extremely low-flow situation make a venous
malformation very difficult to characterize with CT.
■ Ultrasound and MRI are the modalities of choice.

31. LIMITATIONS AND RISKS
Radiation Dose
■ The dose per examination has increased significantly and can now be up to 10
times the amount of radiation delivered by the older 10-mm sequential-
slice scanners.
■ It is estimated that between 1991 and 1996, 0.4% of all cancers in the United
States were attributable to CT studies.
■ As a result of the increased use of CT in the last decade, this figure has
increased to 1.5% to 2%

32. LIMITATIONS AND RISKS
Contrast-Induced Nephropathy
■ The large dosages of contrast have rendered contrast nephropathy the third-
most common cause of iatrogenic acute renal failure.
■ Exact mechanism behind the development of CN remains unknown, but is likely
a combination of direct renal tubule epithelial cell toxicity and renal medullary
ischemia.

33. COMMON ARTIFACTS
Partial-Volume Effects
■ Partial volume refers to a situation in which objects are only partly included
within the scan plane. The resulting image simulates a lesion where none exists.
■ A good example of this effect is, for instance, the appearance of a “nonexisting”
lung nodule adjacent to the anterior attachment of the first rib

34. Beam-Hardening Artifacts
■ Streak artifact or scatter artifact arises from interfaces between materials with
large differences in density from the surrounding structures.
■ commonly seen with dense materials such as prosthetic hips or metallic stents
in endografts.
■ Tantalum and gold stents cause significant beamlike artifacts, whereas
platinum has almost no influence on the image.
■ Steel lies in the middle of the spectrum.
■ These artifacts can result in the erroneous interpretation of vessel lumen
narrowing— sometimes by 25% to 50%.
■ Tantalum and gold cause few effects on MRI images.

35. Beam-Hardening Artifacts
■ Scatter also can occur as a result of dense intravenous contrast material in the
subclavian or brachiocephalic veins because dense contrast is often infused
rapidly into these veins during the scan.
■ If the aortic arch vessels are the focus of the CT scan, the contrast agent should
be infused into the arm opposite the vessel of interest or into the inferior vena
cava.
■ Beam-hardening artifacts can also be seen if both arms are left alongside the
body while scanning the chest.
■ To avoid these artifacts, the patient should be positioned with at least one arm,
preferably both arms, above the head

36. Motion Artifacts
■ Different types of motion artifact exist, but the most pronounced is due to
movement of the patient during the scan.
■ Other well-known motion artifacts are respiratory artifacts.
■ The degree of degradation of the resulting image depends on the degree of
movement and ranges from a double contour to double visibility of the body.
■ To avoid respiratory artifacts in dyspneic patients, the general recommendation
is to ask these patients to maintain shallow respiration.

37. Other Common Artifacts
Averaging artifact
■ “Missing” a small vessel because of surrounding soft tissue.
■ In this type of artifact, the large attenuation from a small calcified plaque within
CT slice “averages” with thrombus-density material to produce a display with
an intermediate density— similar to intraluminal contrast.
■ This artifact often occurs within aortic aneurysms and should be suspected
when contrast-density material appears with no apparent inflow or outflow
vessel and when a piece of calcium or metal is nearby.
■ This type of artifact is reduced by using a small reconstruction interval.

38. Other Common Artifacts
Stair-step artifact
■ Occurs when the reconstruction interval on a spiral CT scan is too large
and a stepped appearance in the vessels is created.
■ This artifact is most likely to occur in vessels oriented away from the direction of
the scan (e.g., renal or iliac arteries).
■ If such an appearance is noted in a multiplanar reformat, it is difficult to evaluate
potential occlusive disease

39. Other Common Artifacts
■ A number of scanner-related artifacts are also possible.
■ Most are related to scanner malfunction, improper calibration (ring artifacts),
tube malfunction, or detector malfunction

40. MAGNETIC
RESONANCE
IMAGING

41. BASIC PRINCIPLES
■ The details of the external magnetic field, magnetic field gradients, and applied
oscillating magnetic field determine characteristics of MR images.
■ The goal of the external magnetic field is to magnetize the subject and make
protons within the subject align parallel with the external field.
■ The physical characteristics of the protons and the size of the external
magnetic field define the resonance frequency of the proton.
■ If the external magnetic field is uniform, all the protons will resonate at the same
frequency.

42. BASIC PRINCIPLES
■ Most MRI machines operate at an external field strength of 1.5 or 3 tesla (T)
■ Lower field systems, those less than 1.0 T, tend to produce images at a
slower rate or at a lower resolution and not desirable for MRA examinations.
■ Magnetic field gradients alter the otherwise uniform external magnetic field in a
linear fashion .
■ The gradients ramping on and off produce the noise heard when an MR image
is being made.
■ The speed and strength of the gradients determine the size of the images
and may be a rate-limiting step in imaging speed

43. Characteristics of MR Images
■ The contrast in MR images depends on the characteristics of the object being
imaged and on the specifics of the sequence itself.
■ Images are typically referred to as either T1 weighted or T2 weighted.
■ T2-weighted images display simple fluids, such as urine, bile, and cerebrospinal
fluid, as bright and other tissues as lower signal.
■ T2-weighted imaging is one of the basic sequences for imaging of tumors but is not
used for angiographic imaging.
■ MRA and magnetic resonance venography (MRV) are performed with T1-weighted
image sequences.
■ Objects that are bright on T1-weighted images, including fat, methemoglobin and
MRI contrast agents, will often be seen on MRA as well.

44. MR Pulse Sequences and
Parameters
■ All pulse sequences have fundamental parameters known as echo time (TE) and
repetition time (TR) that determine image contrast.
■ T2-weighted images have a longer TE, in the range of 80 milliseconds or more, and
a longer TR, in the range of several seconds.
■ Because of the long TE and TR, these sequences are slower and not appropriate for
contrast-enhanced MRA.
■ T1-weighted images, however, have a very short TR and TE, with a TE of 1
millisecond or less and a TR ranging from hundreds of milliseconds to less than 10
milliseconds for MRA sequences.
■ These fast T1-weighted gradient-echo sequences are used for most angiographic
examinations

45. MR Pulse Sequences and
Parameters
■ Other parameters -field of view (FOV) and image matrix.
■ FOV is the size of the imaged region.
■ In a two-dimensional (2D) image, FOV may be 40 x 30 cm with a slice
thickness of 5 mm.
■ The resolution of the image in that 5-mm slice will depend on the number of
pixels within the 30 x 40-cm region.
■ Most MRA, is performed with a three-dimensional (3D) image sequence. In this
case, FOV is specified with three dimensions.

46. MR Angiography and Venography
Non–Contrast-Enhanced MR
Angiography
■ TOF angiography uses a rapid T1-weighted pulse sequence in either
sequentially acquired 2D slices or a 3D imaging slab.
■ In a single-slice image when data are gathered rapidly, the protons within
the slice lose much of their magnetization.
■ The rapid imaging does not degrade any protons outside the slice.
■ When fully magnetized protons in a vessel flow into the slice of interest,
they produce much greater signal than the surrounding tissue.
■ This results in an image in which the blood flowing into the slice is much
brighter than surrounding tissue.

47. Contrast-Enhanced MR Angiography
■ Currently, MR contrast agents approved by the FDA, include several in which
the rare earth element gadolinium is chelated with another substance to avoid
release of toxic free gadolinium into the body.
■ These agents are designed to shorten the T1 of the protons in the vicinity,
thereby making them more conspicuous on T1-weighted imaging sequences

48. Contrast-Enhanced MR Angiography
• MRI is designed not to image the agent itself but to image its effect on protons
in the surrounding water.
• Very small amount of MR contrast material produces effect on multiple water
molecules, similar quantity of iodinated contrast material is not detectable in
CTA or catheter angiography
• Other advantages of gadolinium-based contrast agents include decreased
nephrotoxicity and a lower incidence of reactions to the contrast agent.

49. Step-Table MR Angiography
■ For imaging of a large volume, such as the entire aorta or a peripheral runoff
study, acquisition of data from the entire volume of interest is impractical and
may lead to decreased image quality.
■ The spatial resolution of the acquired images is inversely proportional to the
image matrix size
■ Image matrix size has a direct impact on the duration of the acquisition, so a
higher resolution image requires a longer time to acquire.

50. Step-Table MR Angiography
■ Intravenously administered contrast material will flow from the aortic root to
distal vessels in a time dependent on the rate and volume of injection, the
patient’s cardiac output, and the presence of any proximal occlusive disease
■ Not all portions of the arterial system will be enhancing optimally at the same
time.
■ Steptable acquisition : portions of the anatomy of interest are imaged
sequentially, with the scanner table moving between stations to place the
specific anatomy of interest near the isocenter of the magnet.

51. Step-Table MR Angiography
■ A peripheral runoff study include four step-table stations—abdomen/pelvis,
thighs, calves, and feet—each imaged with a coil, FOV, spatial resolution and
orientation optimized to the particular vascular anatomy in that station
■ Step-table MRA requires additional hardware, including a set of MRI coils for
optimal imaging of each anatomic segment and (usually) optional software to
control the automated table motion.
■ Disadvantage of the step-table technique may be a longer total acquisition
time, which can lead to venous contamination in the later stations.

52. CLINICAL APPLICATIONS OF MR
ANGIOGRAPHY
Renovascular Disease
■ 3D gadolinium enhanced MRA has become a clinical standard.
■ MRA useful in - Atherosclerotic renal artery stenosis , also for evaluating
more subtle renal vascular conditions, such as Fibromuscular dysplasia, renal
artery aneurysms and accessory renal arteries.
■ Detection of accessory arteries is particularly important for assessment of
potential living renal donors
■ 3D contrast-enhanced MRA has a sensitivity of 94% and a specificity of 93%.

53. A, Coronal 3D MR angiogram showing subtle fibromuscular dysplasia ,is isolated to the distal
portion of the main renal artery.
B, Coronal 3D MR angiogram showing right-sided fibromuscular dysplasia and a left-sided renal
artery aneurysm

54. Coronal 3D MR angiogram showing two main renal arteries and four
accessory arteries (seen in 45% of patients).

55. Peripheral Vascular Disease
■ MRA has become a standard method for evaluation of peripheral vascular
disease
■ Effective in the preoperative assessment of patients with peripheral vascular
disease, including imaging of inflow vessels and evaluation of stenosis
■ Sensitivity for detecting hemodynamically significant stenoses is 99.5% with a
specificity of 98.8% compared with digital subtraction angiography (DSA)

56. Coronal 3D MRA step-table
examination

58. CLINICAL APPLICATIONS OF MR
ANGIOGRAPHY
■ MRA can be used to assess graft patency and stenosis.
■ MRA is also a useful technique for demonstrating complications of graft
placement, such as pseudoaneurysm formation,

60. Carotid Vascular Disease
■ Increasingly used method for evaluating carotid artery atherosclerosis
■ For stenosis of between 70% and 99% narrowing, MRA has a reported
sensitivity of 95% and a specificity of 90%.
■ For all stenoses, MRA has a reported sensitivity of 98% and a specificity of 86%

61. Aortic Vascular Disease
■ Assessment of the aortic arch by contrast-enhanced MRA may be superior to
any other technique

62. A Sagittal oblique reformatted MR angiogram of a normal aortic arch.
B Sagittal oblique reformatted MR angiogram of a bovine arch.
C Sagittal oblique reformatted image of a rare arch anomaly, bicarotid truncus. All four vessels arise
separately from the arch. The carotids arise anteriorly and the subclavians posteriorly.

63. A, Sagittal oblique reformatted MR angiogram showing a type B dissection. The origin of the flap and
filling of the proximal false lumen are seen. A separate origin of the left vertebral artery is seen from the
aortic arch .
B, Coronal 3D MR angiogram obtained during the same examination at the thoracoabdominal aorta.

64. Mesenteric Vascular Disease
■ Evaluate those with suspected intestinal angina or chronic mesenteric ischemia.
■ MRA is between 95% and 97% accurate for characterizing proximal disease of
the superior mesenteric artery in cases of chronic mesenteric ischemia.
■ In suspected mesenteric venous thrombosis, MRV can be an extremely useful
tool and has been suggested to be superior to mesenteric catheter
angiography.
■ MRV is particularly successful because of the ease of detecting small amounts
of MR contrast material

65. Venous Vascular Disease
■ MRV is a useful technique for evaluating both central and deep venous
structures.
■ Central venous structures, in particular the superior vena cava, can be
evaluated with 3D methods with 100% sensitivity for the detection of
thrombus compared with DSA.
■ For pelvic and deep venous structures, it is more common to use 2D TOF
angiography

66. Other Applications
■ Assess patients with suspected thoracic outlet syndrome if the appropriate
image sequences can be combined with maneuvers to elicit the symptom
A Coronal 3D MR angiogram showing a normal right subclavian vein with the patient’s arm lowered.
B Occlusion of the subclavian vein near the junction with the axillary vein.

67. LIMITATIONS AND RISKS
Scan Artifacts
Fat Saturation in Chest MR Angiography
■ Suppressing the signal from fat may be advantageous in that fat will have high
signal on the T1-weighted images used for MRA.
Artifacts from gadolinium
■ At high concentrations, MR contrast material behaves like a small piece of metal
and produces a susceptibility artifact on the surrounding tissues.

68. GFR (mL/min/1.73 m2) = 175 × (Scr)-1.154 × (Age)-0.203 × (0.742 if female) × (1.212 if African American)

70. ARTERIOGRAPHY

71. ■ Arteriography remains “Gold Standard”
■ Equipment- venue, hardware, catheters, contrast agents, digital software
■ Angiography can be performed with portable fluroscopy unit or in a designated
IR suite or hybrid operating rooms
■ Fixed mount can provide 10 times resolution as of portable ones
■ Endhole catheters vs flush catheters

72. ■ Contrast agents:
■ High osmolar(1500 to 1700 mOsm)
■ Low osmolar
■ Iso osmolar
■ Ionic contrast agents dissociate into cations and anions when placed in a solution
■ Iodinated atom absorbs x-ray photons and responsible for contrast
visualization
■ Co2 angiography – injection of gas with its decreased radiodensity
creates contrast by transiently displacing blood

73. ■ Delivery of contrast- manual/ power injector
■ DSA- amplification of captured fluroscopic images and digitalized
■ Pixel shifting provides clear image when movement occur after contrast
injection
■ In automatic mode it removes the motion artifact and gives clear image
■ Roadmapping and measuring- real time image superimposed on DSA image

74. ■ Single injection multiple linear field arteriography
■ Rotational arteriography- image intensifier rotates b/w
90-213 degrees
 Maximixing image quality :
- Limiting patient movement
- Administration of anxiolytic and narcotic meds
- Breathing maneuvers

76. ■ Risk from contrast agents
■ CIN and contrast allergy
■ Cardiac toxicity- contrast agents bind to ca and induce arrythmias
■ Hematological toxicity- inhibit coagulation factors and antithrombin 3 activity
■ Lactic acidosis
■ Prevention of CIN
■ Co2 angiography- mesentric ischemia secondary to gas trapping

77. THANK YOU