Thermal reactors—today's typical power reactors—represented the first part of Bhabha's vision. Thermal reactors use slow or thermal energy neutrons to fission uranium-235, a naturally occurring fissile isotope of uranium.
Bhabha envisioned that, in a second stage, spent fuel from these thermal reactors would be reprocessed to separate plutonium for fueling breeder reactors, which would "breed" more plutonium.
In the third and final stage, this plutonium would fuel reactors that would irradiate thorium to make uranium-233.
If India were able to develop the thorium fuel cycle, it could have available as much as 155,502 gigawatt-years of electrical energy (GWe-yr), in comparison to the potential for 328 GWe-yr from indigenously fueled thermal reactors; 10,660 GWe-yr from indigenous coal (which now provides 69 percent of Indian electricity); and 42,231 GWe-yr from plutonium breeder reactors.[1] Currently, India has an installed electrical generating capacity of about 140 GWe, and the rate of electricity demand is expected to increase by 6 to 8 percent per year through 2020 during this period of projected ambitious economic growth.[2] Thus, the thorium cycle holds out the potential to provide a huge portion of India's projected electricity needs for several hundred years.
Indian engineers have recognized, however, that significant hurdles block the way toward commercializing the thorium fuel cycle. High costs and major technical problems are likely to delay full commercialization of the thorium cycle until at least 2050, according to Indian energy experts.
To fully realize the thorium cycle, Indian engineers first face the mainly financial challenge of proving the commercial viability of the plutonium breeder program. India has operated a small 40-megawatt pilot-scale breeder reactor since 1985.Although India is building a commercial-scale breeder reactor, which is projected to be completed in 2011, and is planning to build four more of these reactors by 2020, ramping up to a fleet of breeder reactors will likely take decades, and it is uncertain if this program will succeed commercially. Thus, full realization of
Indeed, after nearly half a century of investment, nuclear energy provides only about 4,000 megawatts of electricity, or 3 percent of
ENDNOTES
1. Subhinder Thakur, Interview with author, Mumbai, January 4, 2008. Similar estimates appear in R. B. Grover and Subhash Chandra, "Scenario for Growth of Electricity in
2. John Stephenson and Peter Tynan, "Will the U.S.-India Civil Nuclear Cooperation Initiative Light India?" in Gauging U.S. Indian Strategic Cooperation, Henry Sokolski, editor (Strategic Studies Institute, 2007), p. 24.
Charles D. Ferguson
If the U.S.-Indian nuclear deal were to move forward without any conditions, it would allow
Second-strike capability demands survivable nuclear forces. To achieve this, Indian analysts have borrowed from the U.S.-Soviet experience during the Cold War and have sought to acquire nuclear-armed submarines. In late February,
The Indian military has been less successful in building nuclear submarines from which to launch such missiles.
Despite the substantial delays in deploying nuclear-powered submarines, these types of warships are not essential for deploying nuclear-armed forces at sea.
At this stage,
The other two legs of the triad would also require ready-to-deploy nuclear weapons. In the absence of clarifying information from the Indian government, there has been considerable debate about the deployment status of
There is even more certainty about the numbers of aircraft
Although the number of nuclear-armed land-based missiles is also uncertain, tests of these missiles are easier to track. The Prithvi I, with a range of 150 kilometers and a payload of 1,000 kilograms, has been approved for the Indian army. The Dhanush is the naval version of the Prithvi II, which is under development and has a range of approximately 350 kilometers. In addition,
Perceived pressures to deter
Plutonium Production
To be sure, Indian officials I interviewed, as well as some deal supporters in the United States, contend that whether or not the deal goes through will not significantly affect India's weapons-grade plutonium production.[4] Given New Delhi's dedication to maintaining such production at full capacity, the deal's potential impact in this regard is indeed murky.
It does appear that, in at least one respect, the deal could stimulate near-term growth in weapons-grade plutonium production. Under the deal,
In addition to its weapons-grade plutonium stockpile, with or without the deal,
The most direct and immediate means of using this material would be as fissile material in nuclear weapons. Although weapons-grade plutonium is ideal for weapons use, reactor-grade plutonium can also serve this purpose.[8] Reportedly,
Moreover, this feedstock of unsafeguarded plutonium could fuel
It should be noted that, in a few years, the deal might lower the future rate of production of reactor-grade plutonium. Without the deal,
Therefore, the deal would serve to lower
Directing
To truly bring
Nuclear trade should be contingent on
Although most Indian policymakers and analysts have supported the country's unilateral testing moratorium since 1998, all interviewees agreed that
Acknowledging
All of the five original nuclear-weapon states, including
Similarly, fissile material production depends crucially on Chinese and Pakistani production. All of the five legally recognized nuclear-weapon states but
Although turning back the growth in
Arms Control Today April 2008
Reshaping the U.S.-Indian Nuclear Deal to Lessen the Nonproliferation Losses
Charles D. Ferguson
For decades,
The tension between
To the Indian government, the civil nuclear cooperation agreement it signed with the
For the deal to go forward, the 45 members of the voluntary Nuclear Suppliers Group (NSG) must first agree to carve out an exception for
The U.S. Congress too must sign off on the final nuclear cooperation agreement, meaning that it and the NSG will retain considerable leverage over
The NSG has an opportunity to condition this exception on
Two Intertwined Visions
The roots of the current controversy over the nuclear deal go back to
This vision of self-sufficiency, which arose in part from
Moreover, while Bhabha sought to ensure that fissile materials would be available for a nuclear weapons program,
Complications during Peritoneal Dialysis
The major complications of peritoneal dialysis are peritonitis, catheter-associated nonperitonitis infections, weight gain a disturbances, and residual uremia (especially among patients with no residual kidney function).
Peritonitis typically develops when there has been a break in sterile technique during one or more of the exchange proc defined by an elevated peritoneal fluid leukocyte count (100/mm3, of which at least 50% are polymorphonuclear neutro presentation typically consists of pain and cloudy dialysate, often with fever and other constitutional symptoms. The mo organisms are gram-positive cocci, including Staphylococcus, reflecting the origin from the skin. Gram-negative rod infe fungal and mycobacterial infections can be seen in selected patients, particularly after antibacterial therapy. Most cases managed either with intraperitoneal or oral antibiotics, depending on the organism; many patients with peritonitis do no cases where peritonitis is due to hydrophilic gram negative rods (e.g., Pseudomonas sp.) or yeast, antimicrobial therapy and catheter removal is required to ensure complete eradication of infection. Nonperitonitis catheter-associated infection infections) vary widely in severity. Some cases can be managed with local antibiotic or silver nitrate administration, whi enough to require parenteral antibiotic therapy and catheter removal.
Peritoneal dialysis is associated with a variety of metabolic complications. As noted above, albumin and other proteins c peritoneal membrane in concert with the loss of metabolic wastes. The hypoproteinemia induced by peritoneal dialysis o protein intake in order to maintain nitrogen balance. Hyperglycemia and weight gain are also common complications of hundred calories in the form of dextrose are absorbed each day, depending on the concentration employed. Peritoneal d those with type II diabetes mellitus, are then prone to other complications of insulin resistance, including hypertriglycer side, the continuous nature of peritoneal dialysis usually allows for a more liberal diet, due to continuous removal of pot two major dietary components whose accumulation can be hazardous in ESRD.
GLOBAL PERSPECTIVE
PERITONEAL DIALYSIS
In peritoneal dialysis, 1.5-3 L of a dextrose-containing solution is infused into the peritoneal cavity and allowed to dwel usually 2-4 h. As with hemodialysis, toxic materials are removed through a combination of convective clearance genera and diffusive clearance down a concentration gradient. The clearance of solutes and water during a peritoneal dialysis e balance between the movement of solute and water into the peritoneal cavity versus absorption from the peritoneal cav diminishes with time and eventually stops when equilibration between plasma and dialysate is reached. Absorption of so peritoneal cavity occurs across the peritoneal membrane into the peritoneal capillary circulation and via peritoneal lymp circulation. The rate of peritoneal solute transport varies from patient to patient and may be altered by the presence of drugs, and physical factors such as position and exercise.
Forms of Peritoneal Dialysis
Peritoneal dialysis may be carried out as continuous ambulatory peritoneal dialysis (CAPD), continuous cyclic peritoneal combination of both. In CAPD, dialysis solution is manually infused into the peritoneal cavity during the day and exchan daily. A nighttime dwell is frequently instilled at bedtime and remains in the peritoneal cavity through the night. The dra performed manually with the assistance of gravity to move fluid out of the abdomen. In CCPD, exchanges are performe usually at night; the patient is connected to an automated cycler that performs a series of exchange cycles while the pa exchange cycles required to optimize peritoneal solute clearance varies by the peritoneal membrane characteristics; as suggest careful tracking of solute clearances to ensure dialysis "adequacy."
Peritoneal dialysis solutions are available in volumes typically ranging from 1.5 to 3.0 L. Lactate is the preferred buffer i solutions. The most common additives to peritoneal dialysis solutions are heparin to prevent obstruction of the dialysis c and antibiotics during an episode of acute peritonitis. Insulin may also be added in patients with diabetes mellitus.
Access to the Peritoneal Cavity
Access to the peritoneal cavity is obtained through a peritoneal catheter. Catheters used for maintenance peritoneal dia made of silicon rubber with numerous side holes at the distal end. These catheters usually have two Dacron cuffs to pro proliferation, granulation, and invasion of the cuff. The scarring that occurs around the cuffs anchors the catheter and s tracking from the skin surface into the peritoneal cavity; it also prevents the external leakage of fluid from the peritonea placed in the preperitoneal plane and ~2 cm from the skin surface.
The peritoneal equilibrium test is a formal evaluation of peritoneal membrane characteristics that measures the transfer glucose across the peritoneal membrane. Patients are classified as low, low-average, high-average, and high "transpor equilibration (i.e., high transporters) tend to absorb more glucose and lose efficiency of ultrafiltration with long daytime also tend to lose larger quantities of albumin and other proteins across the peritoneal membrane. In general, patients w characteristics require more frequent, shorter dwell time exchanges, nearly always obligating use of a cycler for feasibil average) transporters tend to do well with fewer exchanges. The efficiency of solute clearance also depends on the volu Larger volumes allow for greater solute clearance, particularly with CAPD in patients with low and low-average transpor Interestingly, solute clearance also increases with physical activity, presumably related to more efficient flow dynamics
As with hemodialysis, the optimal dose of peritoneal dialysis is unknown. Several observational studies have suggested and creatinine clearance (the latter generally measured in L/week) are associated with lower mortality rates and fewer u However, a randomized clinical trial (ADEMEX) failed to show a significant reduction in mortality or complications with a in urea clearance. In general, patients on peritoneal dialysis do well when they retain residual kidney function. The rates increase with years on dialysis and have been correlated with loss of residual function to a greater extent than loss of p capacity. Recently, a nonabsorbable carbohydrate (icodextrin) has been introduced as an alternative osmotic agent. Stu more efficient ultrafiltration with icodextrin than with dextrose-containing solutions. Icodextrin is typically used as the "l CCPD or for the longest dwell in patients on CAPD. For some patients in whom CCPD does not provide sufficient solute c approach can be adopted where one or more daytime exchanges are added to the CCPD regimen. While this approach c clearance and prolong a patient's capacity to remain on peritoneal dialysis, the burden of the hybrid approach can be ov
Complications during Hemodialysis
Hypotension is the most common acute complication of hemodialysis, particularly among diabetics. Numerous factors ap hypotension, including excessive ultrafiltration with inadequate compensatory vascular filling, impaired vasoactive or au osmolar shifts, overzealous use of antihypertensive agents, and reduced cardiac reserve. Patients with arteriovenous fis develop high output cardiac failure due to shunting of blood through the dialysis access; on rare occasions, this may nec fistula or graft. Because of the vasodilatory and cardiodepressive effects of acetate, its use as the buffer in dialysate wa hypotension. Since the introduction of bicarbonate-containing dialysate, dialysis-associated hypotension has become les management of hypotension during dialysis consists of discontinuing ultrafiltration, the administration of 100 23% saturated hypertonic saline, and administration of salt-poor albumin. Hypotension during dialysis can frequently be evaluation of the dry weight and by ultrafiltration modeling, such that more fluid is removed at the beginning rather tha procedure. Additional maneuvers include the performance of sequential ultrafiltration followed by dialysis; the use of mi adrenergic pressor agent; cooling of the dialysate during dialysis treatment; and avoiding heavy meals during dialysis. Muscle cramps during dialysis are also a common complication of the procedure. The etiology of dialysis-associated cram Changes in muscle perfusion because of excessively aggressive volume removal, particularly below the estimated dry w sodium-containing dialysate, have been proposed as precipitants of dialysis-associated cramps. Strategies that may be include reducing volume removal during dialysis, ultrafiltration profiling, and the use of higher concentrations of sodium modeling (see above).
Anaphylactoid reactions to the dialyzer, particularly on its first use, have been reported most frequently with the bioinco containing membranes. With the gradual phasing out of cuprophane membranes in the
diseases constitute the major causes of death in patients with ESRD. Cardiovascular mortality and event patients than in patients posttransplantation, although rates are extraordinarily high in both populations. The underlying disease is unclear but may be related to shared risk factors (e.g., diabetes mellitus), chronic inflammation, massive cha volume (especially with high interdialytic weight gains), inadequate treatment of hypertension, dyslipidemia, anemia, dy calcification, hyperhomocysteinemia, and, perhaps, alterations in cardiovascular dynamics during the dialysis treatment cardiovascular risk reduction in ESRD patients; none have demonstrated consistent benefit. Nevertheless, most experts cardioprotective strategies (e.g., lipid-lowering agents, aspirin, -adrenergic antagonists) in dialysis patients based on t risk profile, which appears to be increased by more than an order of magnitude relative to persons unaffected by kidney
DIALYSIS ACCESS
The fistula, graft, or catheter through which blood is obtained for hemodialysis is often referred to as a dialysis access the anastomosis of an artery to a vein (e.g., the Brescia-Cimino fistula, in which the cephalic vein is anastomosed end results in arterialization of the vein. This facilitates its subsequent use in the placement of large needles (typically 15 ga circulation. Although fistulas have the highest long-term patency rate of all dialysis access options, fistulas are created i the United States. Many patients undergo placement of an arteriovenous graft (i.e., the interposition of prosthetic mate polytetrafluoroethylene, between an artery and a vein) or a tunneled dialysis catheter. In recent years, nephrologists, v health care policy makers in the United States have encouraged creation of arteriovenous fistulas in a larger fraction of initiative). Unfortunately, even when created, arteriovenous fistulas may not mature sufficiently to provide reliable acce they may thrombose early in their development. Novel surgical approaches (e.g., brachiobasilic fistula creation with tran fistula to the arm surface) have increased options for "native" vascular access.
Grafts and catheters tend to be used among persons with smaller-caliber veins or persons whose veins have been dama venipuncture, or after prolonged hospitalization. The most important complication of arteriovenous grafts is thrombosis failure, due principally to intimal hyperplasia at the anastomosis between the graft and recipient vein. When grafts (or f guided angioplasty can be used to dilate stenoses; monitoring of venous pressures on dialysis and of access flow, thoug may assist in the early recognition of impending vascular access failure. In addition to an increased rate of access failur catheters are associated with much higher rates of infection than fistulas.
Intravenous large-bore catheters are often used in patients with acute and chronic kidney disease. For persons on main tunneled catheters (either two separate catheters or a single catheter with two lumens) are often used when arterioven failed or are not feasible due to anatomical considerations. These catheters are tunneled under the skin; the tunnel redu from the skin, resulting in a lower infection rate than with nontunneled temporary catheters. Most tunneled catheters ar
jugular veins; the external jugular, femoral, and subclavian veins may also be used. Nephrologists, interventional radiol surgeons generally prefer to avoid placement of catheters into the subclavian veins; while flow rates are usually excelle frequent complication and, if present, will likely prohibit permanent vascular access (i.e., a fistula or graft) in the ipsilat rates may be higher with femoral catheters. For patients with multiple vascular access complications and no other optio access, tunneled catheters may be the last "lifeline" for hemodialysis. Translumbar or transhepatic approaches into the required if the superior vena cava or other central veins draining the upper extremities are stenosed or thrombosed.
Goals of Dialysis
The hemodialysis procedure is targeted at removing both low- and high-molecular-weight solutes. The procedure consis blood through the dialyzer at a flow rate of 300-500 mL/min, while dialysate flows in an opposite counter-current The efficiency of dialysis is determined by blood and dialysate flow through the dialyzer as well as dialyzer characteristic removing solute). The dose of dialysis, which is currently defined as a derivation of the fractional urea clearance during is further governed by patient size, residual kidney function, dietary protein intake, the degree of anabolism or catabolis comorbid conditions.
Since the landmark studies of Sargent and Gotch relating the measurement of the dose of dialysis using urea concentra National Cooperative Dialysis Study, the delivered dose of dialysis has been measured and considered as a quality assur tool. While the fractional removal of urea nitrogen and derivations thereof are considered to be the standard methods b dialysis" is measured, a large multicenter randomized clinical trial (the HEMO Study) failed to show a difference in morta difference in urea clearance. Still, multiple observational studies and widespread expert opinion have suggested that hig warranted; current targets include a urea reduction ratio (the fractional reduction in blood urea nitrogen per hemodialys and a body water-indexed clearance x time product (KT/V) above 1.3 or 1.05, depending on whether urea concentration For the majority of patients with ESRD, between 9 and 12 h of dialysis are required each week, usually divided into thre studies have suggested that longer hemodialysis session lengths may be beneficial, although these studies are confound characteristics, including body size and nutritional status. Hemodialysis "dose" should be individualized, and factors othe should be considered, including the adequacy of ultrafiltration or fluid removal. Several authors have highlighted improv associated with more frequent hemodialysis (i.e., more than three times a week), although these studies are also confo A randomized clinical trial is currently underway to test whether more frequent dialysis results in differences in a variety functional markers.
The Dialyzer
There are three essential components to hemodialysis: the dialyzer, the composition and delivery of the dialysate, and The dialyzer consists of a plastic device with the facility to perfuse blood and dialysate compartments at ve surface area of modern dialysis membranes in adult patients is usually in the range of 1.5-2.0 m2. The hollow use in the
Recent advances have led to the development of many different types of membrane material. Broadly, there are four ca membranes: cellulose, substituted cellulose, cellulosynthetic, and synthetic. Over the past three decades, there has bee cellulose-derived to synthetic membranes, because the latter are more "biocompatible." Bioincompatibility is generally d membrane to activate the complement cascade. Cellulosic membranes are bioincompatible because of the presence of f membrane surface. In contrast, with the substituted cellulose membranes (e.g., cellulose acetate) or the cellulosyntheti groups are chemically bound to either acetate or tertiary amino groups, resulting in limited complement activation. Syn polysulfone, polymethylmethacrylate, and polyacrylonitrile membranes, are even more biocompatible because of the ab groups. Polysulfone membranes are now used in >60% of the dialysis treatments in the United States. Reprocessing and reuse of hemodialyzers are often employed for patients on maintenance hemodialysis in the United St manufacturing costs for disposable dialyzers have declined, more and more outpatient dialysis facilities are no longer re most centers employing reuse, only the dialyzer unit is reprocessed and reused, whereas in the developing world blood reused. The reprocessing procedure can be either manual or automated. It consists of the sequential rinsing of the bloo compartments with water, a chemical cleansing step with reverse ultrafiltration from the dialysate to the blood compart patency of the dialyzer, and, finally, disinfection of the dialyzer. Formaldehyde, peracetic acid-hydrogen peroxide, gluta all been used as reprocessing agents.
Dialysate
The potassium concentration of dialysate may be varied from 0 to 4 mmol/L depending on the predialysis plasma potass usual dialysate calcium concentration in U.S. hemodialysis centers is 1.25 mmol/L (2.5 meq/L), although modification m settings (e.g., higher dialysate calcium concentrations may be used in patients with hypocalcemia associated with secon or following parathyroidectomy). The usual dialysate sodium concentration is 140 mmol/L. Lower dialysate sodium conc with a higher frequency of hypotension, cramping, nausea, vomiting, fatigue, and dizziness. In patients who frequently their dialysis run, "sodium modeling" to counterbalance urea-related osmolar gradients is often used. When sodium mod concentration is gradually lowered from the range of 145-155 meq/L to isotonic concentrations (140 meq/L) near the e treatment, typically declining either in steps or in a linear or exponential fashion. Because patients are exposed to appro during each dialysis treatment, water used for the dialysate is subjected to filtration, softening, deionization, and, ultim During the reverse osmosis process, water is forced through a semipermeable membrane at very high pressure to remo contaminants and >90% of dissolved ions.
Blood Delivery System
The blood delivery system is composed of the extracorporeal circuit in the dialysis machine and the dialysis access. The of a blood pump, dialysis solution delivery system, and various safety monitors. The blood pump moves blood from the dialyzer, and back to the patient. The blood flow rate may range from 250-500 mL/min, depending largely on the type vascular access. Negative hydrostatic pressure on the dialysate side can be manipulated to achieve desirable fluid remo Dialysis membranes have different ultrafiltration coefficients (i.e., mL removed/min per mmHg) so that along with hydro removal can be varied. The dialysis solution delivery system dilutes the concentrated dialysate with water and monitors conductivity, and flow of dialysate.
TREATMENT OPTIONS FOR ESRD PATIENTS
Commonly accepted criteria for initiating patients on maintenance dialysis include the presence of uremic symptoms, th unresponsive to conservative measures, persistent extracellular volume expansion despite diuretic therapy, acidosis ref a bleeding diathesis, and a creatinine clearance or estimated glomerular filtration rate (GFR) below 10 mL/min per 1.73 estimating equations). Timely referral to a nephrologist for advanced planning and creation of a dialysis access, educati options, and management of the complications of advanced chronic kidney disease, including hypertension, anemia, aci hyperparathyroidism, is advisable.
In ESRD, treatment options include hemodialysis (in center or at home); peritoneal dialysis, as either continuous ambul (CAPD) or continuous cyclic peritoneal dialysis (CCPD); or transplantation (Chap. 276). Although there are geographic v remains the most common therapeutic modality for ESRD (>90% of patients) in the United States. In contrast to hemo is continuous, but much less efficient, in terms of solute clearance. While no large-scale clinical trials have been comple among patients randomized to either hemodialysis or peritoneal dialysis, outcomes associated with both therapies are s the decision of which modality to select is often based on personal preferences and quality-of-life considerations.
HEMODIALYSIS
Hemodialysis relies on the principles of solute diffusion across a semipermeable membrane. Movement of metabolic was down a concentration gradient from the circulation into the dialysate. The rate of diffusive transport increases in respon including the magnitude of the concentration gradient, the membrane surface area, and the mass transfer coefficient of is a function of the porosity and thickness of the membrane, the size of the solute molecule, and the conditions of flow o membrane. According to the laws of diffusion, the larger the molecule, the slower its rate of transfer across the membra as urea (60 Da), undergoes substantial clearance, whereas a larger molecule, such as creatinine (113 Da), is cleared les diffusive clearance, movement of waste products from the circulation into the dialysate may occur as a result of ultrafilt clearance occurs because of solvent drag, with solutes being swept along with water across the semipermeable dialysis .
DIALYSIS IN THE TREATMENT OF RENAL FAILURE: INTRODUCTION
Dialysis may be required for the treatment of either acute or chronic kidney disease. The use of continuous renal replac and slow, low-efficiency dialysis (SLED) is specific to the management of acute renal failure and is discussed in Chap. 2 performed continuously (CRRT) or over 6-12 hours per session (SLED), in contrast to the 3-4 hours of an intermittent Advantages and disadvantages of CRRT and SLED.
Peritoneal dialysis is rarely used in developed countries for the treatment of acute renal failure because of the increased will be discussed in more detail below) less efficient clearance per unit of time. The focus of the majority of this chapter dialysis for end-stage renal disease (ESRD).
With the widespread availability of dialysis, the lives of hundreds of thousands of patients with ESRD have been prolong alone, there are now approximately 450,000 patients with ESRD, the vast majority of whom require dialysis. The incide cases per million population per year. The incidence of ESRD is disproportionately higher in African Americans (approxim population per year) as compared with white Americans (259 per million population per year). In the United States, the diabetes mellitus, currently accounting for nearly 45% of newly diagnosed cases of ESRD. Over one-quarter (27%) of p been attributed to hypertension, although it is unclear whether in these cases hypertension is the cause or a consequen other unknown causes of kidney failure. Other important causes of ESRD include glomerulonephritis, polycystic kidney d uropathy.
Globally, mortality rates for patients with ESRD are lowest in Europe and Japan but very high in the developing world b availability of dialysis. In the United States, the mortality rate of patients on dialysis is approximately 18-20% per year of approximately 30-35%. Deaths are due mainly to cardiovascular diseases and infections (approximately 50 and 15% Older age, male sex, nonblack race, diabetes mellitus, malnutrition, and underlying heart disease are important predict
Noninvasive Cardiac Imaging: Echocardiography, Nuclear Cardiology, and MRI/CT Imaging:
Cardiovascular imaging has significantly enhanced the practice of cardiology over the past few decades. Two
(2D) echocardiography is able to visualize the heart directly in real time using ultrasound, providing instantaneous
assessment of the myocardium, cardiac chambers, valves, pericardium, and great vessels. Doppler echocardiography
measures the velocity of moving red blood cells and has become a noninvasive alternative to cardiac catheterization for assessment of hemodynamics. Transesophageal echocardiography (TEE) provides a unique window for high
imaging of posterior structures of the heart, particularly the left atrium, mitral valve, and aorta. Nuclear cardiology uses isotopes to assess myocardial perfusion and ventricular function and has contributed greatly to the evaluation of patient with ischemic heart disease. Cardiac MRI and CT can delineate cardiac structure and function with high resolution. They particularly useful in the examination of cardiac masses, the pericardium, and the great vessels. MRI stress testing is no possible examining both ventricular function and perfusion. Detection of coronary calcification by CT as well as direct
visualization of coronary arteries by CT angiography (CTA) are of growing utility in patients with suspected coronary art disease (CAD). This chapter provides an overview of the basic concepts of these cardiac imaging modalities, as well as t clinical indications for each procedure. The illustrations in this chapter are supplemented by "real time" and other static images in Chap. e20, "The Atlas of Noninvasive Cardiac Imaging."
Two-Dimensional Echocardiography
BASIC PRINCIPLES
2D echocardiography uses the principle of ultrasound reflection off cardiac structures to produce images of the heart (T 222-1). For a transthoracic echocardiogram (TTE), the imaging is performed with a handheld transducer placed directly the chest wall. In selected patients, a TEE may be performed, in which an ultrasound transducer is mounted on the tip o endoscope placed in the esophagus and directed toward the cardiac structures.
Table 1 Clinical Uses of Echocardiography
Two-Dimensional Echocardiography Doppler Echocardiography
Cardiac chambers Valve stenosis
Chamber size Gradient
Left ventricular Valve area
Hypertrophy Valve regurgitation
Regional wall motion abnormalities Semiquantitation
Valve Intracardiac pressures
Morphology and motion Volumetric flow
Pericardium Diastolic filling
Effusion Intracardiac shunts
Tamponade Transesophageal Echocardiography
Masses Inadequate transthoracic images
Great vessels Aortic disease
Stress Echocardiography Infective endocarditis
Two-dimensional Source of embolism
Myocardial ischemia Valve prosthesis
Viable myocardium Intraoperative
Doppler
Valve disease
Current echocardiographic machines are portable and can be wheeled directly to the patient's bedside. Thus, a major
advantage of echocardiography over other imaging modalities is the ability to obtain instantaneous images of the cardia structures for immediate interpretation. Handheld echocardiographic units weighing 6 lb (<2.7 kg) have now become available, further enhancing the ease and portability of echocardiography. They are becoming an essential initial diagno modality for the critically ill patient in the emergency room and critical care setting.
A limitation of TTE is the inability to obtain high-quality images in all patients, especially those with a thick chest wall o severe lung disease, as ultrasound waves are poorly transmitted through lung parenchyma. New technology such as harmonic imaging and IV contrast agents (which traverse the pulmonary circulation) can now be used to enhance
endocardial borders in patients with poor acoustic windows.
CHAMBER SIZE AND FUNCTION
2D echocardiography is an ideal imaging modality for assessing left ventricular (
qualitative assessment of the cavity sizes of the ventricles and systolic function can be made directly from the 2D imag experienced observers. 2D echocardiography is useful in the diagnosis of
Figure 1
Two-dimensional echocardiographic still-frame images from a normal patient with a normal heart. Top: Parasternal l axis view during systole and diastole (left) and systole (right). During systole, there is thickening of the myocardium and reducti the size of the left ventricle (