YEAR IN CARDIOLOGY SERIES
The Year in Cardiac Imaging
Raymond J. Gibbons, MD*,1,*,
Philip A. Araoz, MD and
Eric E. Williamson, MD,2
* Division of Cardiovascular Diseases and Internal Medicine, Department of Medicine, Mayo Clinic and Mayo Foundation, Rochester, Minnesota
Department of Radiology, Mayo Clinic and Mayo Foundation, Rochester, Minnesota.
* Reprint requests and correspondence: Dr. Raymond J. Gibbons, Mayo Clinic, Gonda 5, 200 First Street, SW, Rochester, Minnesota 55905. (Email: gibbons.raymond{at}mayo.edu).
This review is a sequel to our previous reports highlighting the most important recent literature in single-photon emission computed tomography (SPECT) myocardial perfusion imaging, cardiac positron emission tomography (PET), cardiac computed tomography (CT), and cardiac magnetic resonance imaging (MRI). In almost all cases, these studies were published in the English-language literature between April 1, 2006, and March 31, 2007. The decision to arbitrarily include some articles and exclude others is more difficult each year. Time has exposed some of our previous errors. Last year, we did not include the first case report on nephrogenic systemic fibrosis. This year, we added a whole new safety section on this topic. We can assure both authors and readers that we have done our best to put aside personal biases in reaching these difficult decisions. We have again organized this summary around topical themes in an effort to encourage a broad, multimodality approach to the application of imaging to clinical problems.
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Technical Advances
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PET.
Although cardiac F-18 fluorodeoxyglucose (FDG)-PET imaging is a well-established technique, vascular FDG-PET imaging is not. Two studies addressed this emerging area. Tawakol et al. (1) compared the results of FDG-PET imaging with tissue samples obtained during subsequent carotid endarterectomy to demonstrate a significant correlation between FDG uptake and both carotid plaque and macrophage staining. This early study offers great promise if subsequent studies demonstrate that increased carotid FDG activity predicts subsequent cerebrovascular events. Tahara et al. (2) used FDG-PET vascular imaging in a randomized trial of 43 patients to demonstrate a decrease in FDG uptake in patients treated with simvastatin.
CT.
The rapid technical advances in CT continue. Early studies described the use of 256-row cone beam and dual-source CT, both introduced in last year’s review. Using dual-source CT, Johnson et al. (3) demonstrated impressive temporal resolution and robust coronary artery imaging at a wide range of heart rates. Scheffel et al. (4) showed similar results, with excellent negative predictive value for >50% stenosis despite a lack of beta-blockade.
MRI.
Advances in MRI software and computer processing have lead to faster, more robust performance. There is a small-but-growing literature in which MRI acquisitions are acquired in a single breath hold, or in a free-breathing state. Attempts to decrease the breathing requirements for MRI volume measurements are summarized in Table 1
(5–10). The ability to perform MRI acquisitions in a single breath hold, or in a free-breathing state, would substantially reduce the main limitation of MRI (i.e., the level of required patient cooperation).
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Viability
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PET.
Previous studies have reported conflicting data on the duration of survival of hibernating myocardium. Wiggers et al. (11) performed serial sestamibi SPECT and FDG-PET on 16 patients with chronically stunned or hibernating myocardium who were treated with medical therapy for approximately 2 years. Sestamibi and FDG uptake was unchanged in regions of hibernating myocardium and only slightly decreased in regions with chronic stunning, suggesting an adaptation to chronic ischemia (Fig. 1).
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Figure 1 Changes in Sestamibi and FDG Update Over Time
Changes in sestamibi uptake (top) and FDG uptake (bottom) plotted against duration of follow-up. Regression lines are shown for the chronically stunned regions (open circles), which displayed a weak negative linear correlation between duration of follow-up and change in sestamibi uptake (r2 = 0.15, p < 0.0001) and FDG uptake r2 = 0.24, p < 0.001). In hibernating regions (solid circles), there was no significant correlation. FDG = fluorodeoxyglucose. Figure used with permission from Wiggers et al. (11).
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CT.
Although the use of CT to evaluate myocardial viability remains in its infancy, there is widespread interest in using CT as a "one-stop shop" for ischemic cardiac disease. Most new studies used 2 methods for detection of myocardial ischemia and infarction using contrast-enhanced CT: first-pass myocardial enhancement and delayed myocardial hyperenhancement.
In a porcine model, Baks et al. (12) showed that infarct size by delayed enhancement CT correlated closely with histology (r2 = 0.92; p < 0.001). The same group reported excellent correlations between delayed enhancement CT and delayed enhancement MRI (r2 = 0.96; p < 0.001) and between both techniques and pathology (r2 = 0.96 and 0.93, respectively) (13). Brodoefel et al. (14) confirmed these findings in another porcine model and showed that CT characterized microvascular obstruction similarly to MRI and the transmural extent of infarction similarly to both MRI and histology ( = 0.86 and 0.84, respectively). In contrast, they reported that first-pass myocardial enhancement significantly underestimated infarct size and was inaccurate for the determination of infarct transmurality.
In 42 patients, Sanz et al. (15) reported that the sensitivity and specificity of postcontrast CT for the detection of MI (compared with MRI) were 91% and 81%, respectively. There was strong correlation between MI volume by CT as compared with MRI (r = 0.87); however, CT substantially underestimated the volume of infarcted myocardium (2.7 ± 2.5 ml vs. 25.9 ± 19.9 ml). Interestingly, 71% of subjects with MRI evidence of myocardial infarction (MI) exhibited regions of hypoattenuation on precontrast CT images, suggesting that hypoattenuation found on postcontrast CT images may not reflect diminished perfusion.
Nieman et al. (16) evaluated the ability of first-pass CT myocardial enhancement to characterize the chronicity of myocardial infarction in 16 patients with acute myocardial infarction (<1 week), 13 patients with chronic infarction (>1 year), and 13 normal control patients. Mean attenuation, differential attenuation, myocardial wall thickness, and ventricular dimension were significantly different among the 3 groups, and with the use of CT, the authors were able to reliably distinguish between acute and chronic infarction (16).
MRI.
In MRI nonviable, infarcted tissue is most commonly detected using a technique called "delayed enhancement" or "delayed hyperenhancement." The main advantage of MRI delayed enhancement is its spatial resolution of 1 to 2 mm, compared with about 10 mm with Tc99m-sestamibi SPECT scanning. Ibrahim et al. (17) compared MRI with SPECT in 78 patients with acute MI. Using troponin elevation as the reference standard for MI, they found that MRI was significantly more sensitive than SPECT for the detection of small infarcts (troponin < 3.0 ng/ml; 92% vs. 69%; p = 0.03), and infarction in nonanterior location (98% vs. 84%; p = 0.03) (Figs. 2 and 3). Given the excellent prognosis of patients with no infarction by SPECT, future studies will be required to see whether patients with such small infarcts, detectable by MRI and not SPECT, have an adverse prognosis.
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Figure 2 MRI Compared With SPECT for Detection of Small Infarcts
(A) Short-axis magnetic resonance imaging (MRI) delayed-enhancement images show a small subendocardial infarct in the lateral wall (arrowhead). The corresponding short axis Tc99m sestamibi single-photon emission computed tomography (SPECT) images do not show a definite abnormality in this area (arrowhead). (B) Short axis delayed-enhancement MRI image in a different patient shows a small focus of transmural delayed enhancement in the inferolateral wall. The corresponding short axis Tc99m sestamibi SPECT images do not show a definite abnormality in this area (arrowhead). Figure used with permission from Ibrahim et al. (17).
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Figure 3 MRI and SPECT Compared With Troponin Levels
Sensitivity of delayed enhancement contrast-enhanced magnetic resonance imaging (MRI) and single-photon emission computed tomography (SPECT) for the detection of acute myocardial infarction based on the peak troponin T levels (TNT). From the original figure: "Groups were defined by peak troponin T level <3.0 ng/ml (n = 26), 3.0 to 6.0 ng/ml (n = 27), and >6.0 ng/ml (n = 25) (*p = 0.03)." Open bars = MRI; solid bars = SPECT. Figure used with permission from Ibrahim et al. (17).
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Several investigators have used the spatial resolution of MRI delayed enhancement imaging to quantify small infarcts or to map the spatial extent of infarcts or fibrosed tissue (Table 2) (18–21). Porto et al. (18) demonstrated distal embolization of plaque material in 15 of 64 vessels (23%) undergoing PCI with stent placement. The new infarcts detected were only 7.6 ± 6.2 g, which might have been missed by other modalities.
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Safety
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MRI contrast and nephrogenic systemic fibrosis.
The most significant development affecting the practice of MRI has been the proposed causative association between the use of MRI contrast media in patients with advanced renal failure and nephrogenic systemic fibrosis (NSF), an obscure debilitating fibrosing disease, primarily affecting the skin, which was first reported in 2000 (22). In early 2006, Grobner (23) reported that 5 of 9 dialysis patients who had received gadolinium-based MRI contrast media developed NSF within 2 to 4 weeks of exposure to contrast and suggested a possible causal association. Other reports quickly followed (24–27).
In February 2007, High et al. (28) reported the first evidence of causation between gadolinium and NSF. They found that patients with NSF had on average 70 ppm of gadolinium ion in their affected skin, which is 35- to 150-fold greater than the retained levels other investigators have reported in the bones of healthy volunteers. High et al. (28) interpreted these data to support the current prevailing hypothesis (i.e., that the gadolinium ion in MRI contrast disassociates from its carrier molecule and is not excreted but collects in tissue in patients with renal failure). Interested readers are urged to monitor the literature carefully during the coming year, for further studies of the mechanisms for this disease, and further announcements from major professional societies and regulatory agencies.
CT.
Minimizing the radiation dose of CT is an area of great interest. Abada et al. (29) evaluated electrocardiogram (ECG)-pulsed tube current modulation, a technique that reduces the CT tube current during phases of the cardiac cycle deemed unlikely to produce useful images of the coronary arteries. They found that radiation doses could be decreased by up to 88% in thin patients without compromising image quality. Hesse et al. (30) also evaluated tube current modulation using echocardiography to determine the optimal temporal window for maximum tube current. Radiation dose was reduced by 42% and only 3% of coronary segments were unevaluable in the modulation group.
Prospective ECG-triggering, a nonhelical scan technique in which the CT scanner functions in a "step-and-shoot" mode, is experiencing a resurgence. This 20-year-old technique had been almost completely replaced by retrospective ECG-gating to permit acquisition of functional cardiac data. However, this technique provides superior spatial resolution at much lower radiation doses (31). Additional applications of this technique are likely.
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Coronary Artery Disease (CAD)
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Diagnosis.
SPECT
Although the diagnosis of CAD by SPECT is well-defined, 2 studies provided important new insights. Schuijf et al. (32) compared multislice CT with SPECT in 114 patients at intermediate likelihood of CAD. The SPECT findings were almost always normal in patients who did not have CT-confirmed CAD. In patients with obstructive CAD confirmed by CT, 50% had normal SPECT. The accompanying editorial by Dorbala et al. (33) defines the potential application of these results.
Whittle et al. (34) compared positive SPECT scans with subsequent coronary angiography in 52 African American and 259 Caucasian male veterans. African Americans had a lower prevalence and severity of CAD. Further studies are needed to better understand these surprising findings.
Another study addressed a practical issue, the effects of caffeine ingestion on adenosine SPECT imaging. In 30 patients with reversible defects on adenosine SPECT, Zoghbi et al. (35) reported that repeat imaging after 8 ounces of coffee was very similar to the baseline scan, suggesting that the widespread practice of deferring adenosine studies in patients with recent caffeine ingestion may be unnecessary.
The diagnostic application of SPECT may extend to patients with dyspnea without chest pain. In 1,864 such patients, Balaravi et al. (36) found a high prevalence of abnormal (45%) and high-risk (11%) SPECT scans; high-risk scans were associated with a much worse 10-year survival.
PET
Coronary physiology is still not fully defined. Jagathesan et al. (37) demonstrated an inverse relation between myocardial blood flow during dobutamine stress PET and stenosis severity in ischemic territories. Surprisingly, they also demonstrated a similar significant relationship in remote territories, which seemed to be due to an increase in minimal coronary resistance.
PET and CT
Sampson et al. (38) reported promising diagnostic results in 64 patients with suspected CAD using rubidium stress PET and CT for attenuation correction.
CT
The prospective comparison of 64-detector row CT systems to coronary catheterization for the detection of stenosis remains a popular topic for investigation. The technique has been expanded to a broader range of patients (39–50) (Table 3).
Several studies have used CT angiography (CTA) in patients presenting to the emergency department with chest pain (51–55) (Table 4). The biggest advantage of CT in these patients is its ability to evaluate cardiac and noncardiac causes of chest pain simultaneously. A number of recent studies have described significant extracardiac findings discovered during coronary CTA (56–59) (Table 5).
Cardiac CTA is increasingly being used for the evaluation of coronary artery bypass grafts. Malagutti et al. (60) showed 99% sensitivity and 96% specificity for bypass graft disease by segment. Pache et al. (61) demonstrated 98% sensitivity and 89% specificity for bypass graft stenosis or occlusion, with 6% of distal anastomoses not evaluable. Interestingly, several grafts missed by catheterization were visualized with CTA (40). Di Lazzaro et al. (62) used 16-detector row CTA to evaluate radial artery coronary bypass grafts, confirming the accuracy of CT for this indication.
Several studies used CT for the detection of transplant vasculopathy in heart transplant recipients. Gregory et al. (63) demonstrated feasibility of 64-row CT in 20 transplant patients. Although agreement with intravascular ultrasound was limited (sensitivity = 70%, specificity = 92%), coronary artery diameter measurements correlated well with catheter angiography (r2 = 0.89). Iyengar et al. (64) demonstrated good agreement between 64-row CT and catheter angiography for the detection of coronary vasculopathy in 20 transplant patients ( = 0.69). Sigurdsson et al. (65) demonstrated similar good correlation between 16-row CT and coronary angiography for percent stenosis (r = 0.75, p < 0.01).
In a canine model of graded left anterior descending stenosis, George et al. (66) performed CTA during adenosine administration to show that stress-induced flow deficits can be detected by CT and that attenuation values can be used to estimate absolute myocardial blood flow, as measured by microspheres. Although the CT attenuation calculation method is only semiquantitative, their findings suggest that first-pass contrast enhancement has the potential for clinical utility in the evaluation of coronary stenosis.
MRI
Several preliminary studies on direct coronary imaging reported technical measurements, such as signal-to-noise ratio (SNR). In 9 volunteers, Bansmann et al. (67) used a 3-T scanner (one with twice the magnetic field strength of conventional scanners) to compare the length of visible coronary vessels and the SNRs for the vessel wall, epicardial fat, and luminal blood of 2 different types of MRI acquisitions. In 10 volunteers, Bi et al. (68) used a conventional 1.5-T scanner to compare SNR and vessel length in a whole heart and volume-targeted scan. They found longer depicted vessel lengths in the volume targeted scans.
Several researchers have used MRI stress perfusion or stress wall motion imaging to detect CAD. In 92 patients scheduled for clinically-indicated coronary angiography, Klem et al. (69) performed rest wall motion, adenosine-stress perfusion and delayed enhancement infarct imaging at the same MRI examination. Readers then used wall motion, perfusion, and delayed enhancement separately and in various combinations. Magnetic resonance imaging adenosine perfusion had 84% sensitivity and 58% specificity for detecting significant CAD. Using all of the information in a predetermined algorithm, Klem et al. (69) found that sensitivity was similar at 89% and specificity improved to 87%.
In 46 patients, Cury et al. (70) reported that MRI adenosine perfusion had 81% sensitivity and 90% specificity for detecting CAD. The combination of rest perfusion, wall motion analysis, and delayed enhancement had 89% sensitivity and 85% specificity.
CT and MRI
Wang et al. (71) reported on a subset of 222 patients from the MESA (Muli-Ethnic Study of Atherosclerosis) study who underwent both CT imaging for coronary artery calcification and adenosine MRI to assess myocardial perfusion reserve. They found that perfusion reserve was inversely associated with the presence and severity of coronary calcification, suggesting that this was a manifestation of subclinical coronary atherosclerosis in the absence of symptoms in these patients.
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Prognosis
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SPECT.
A variety of studies confirmed the prognostic utility of SPECT (72–76) (Table 6). Mahmarian et al. (77) enrolled 728 stable survivors of acute MI in the prospective multicenter ASPIRE (Adenosine Sestamibi Post-Infarction Evaluation) trial. Using gated adenosine SPECT within 10 days of hospitalization and prospectively defined criteria, they identified low-risk, intermediate-risk, and high-risk subgroups. The low-risk subgroup comprised nearly one-third of all enrolled patients and had only a 1.8% hard event rate during the subsequent year. They suggested that identification of these patients may permit earlier hospital discharge with less intervention.
SPECT and CT.
Rozanski et al. (78) reported outcomes in 1,153 patients who underwent both SPECT and CT for coronary calcification. In patients without ischemia by SPECT, event rates remained low even when calcium scores exceeded 1,000.
PET.
The prognostic utility of stress PET studies is not as well established as SPECT. Yoshinaga et al. (79) examined the prognostic value of myocardial perfusion imaging using PET rubidium-82 imaging. Both hard events and total cardiac events were related to the summed stress score. The annual hard event rate was 0.4% in the normal group and 7.0% in the moderate-to-severe abnormal group. More importantly, PET had prognostic value in patients referred after SPECT imaging, as well as in patients with obesity.
CT.
Gopal et al. (80) performed follow-up CT studies of patients with a negative coronary calcium scan at baseline at a minimum of 12 months later (mean 4 years). A total of 62% of their patients never developed coronary calcium, and only 3% had an increase of more than 50 Agatston units, suggesting that patients with an initial coronary calcium score of zero do not need follow-up evaluation prior to 5 years after the initial scan.
Coronary CTA.
Pundziute et al. (81) followed 100 patients for 16 months after CTA (16- and 64-detector row). Computed tomographic angiography provided prognostic information independent of baseline clinical parameters.
MRI.
Until recently, there have been limited data regarding the prognostic value of cardiac MRI. This year, several studies used MRI delayed enhancement to predict patient outcomes (82–88) (Table 7). Assomull et al. (83) found that the presence of fibrosis predicted mortality in patients with nonischemic cardiomyopathy (Fig. 4). Two papers showed that MRI delayed enhancement predicted the response to cardiac resynchronization therapy (Fig. 5).
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Figure 4 Prognostic Value of MRI Delayed Enhancement
Kaplan-Meier survival estimates for the primary end point of all-cause mortality or hospitalization due to cardiovascular causes. Data are adjusted for baseline differences in age, left ventricular (LV) end-systolic volume, LV end-diastolic volume, LV ejection fraction, right ventricular ejection fraction, and treatment with digoxin. Lower blue/black line indicates patients with late gadolinium enhancement; upper red line indicates patients without late gadolinium enhancement; MRI = magnetic resonance imaging. Figure used with permission from Assomull et al. (83).
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Figure 5 MRI Prediction of Response to Resynchronization
Linear regression plots showing the relationship between total percent scar and change in left ventricular ejection fraction (EF). MRI = magnetic resonance imaging. Figure used with permission from White et al. (86).
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The prognostic significance of MRI stress testing has also been evaluated. Jahnke et al. (89) performed 2.26 ± 1.03 years of follow-up in 461 patients who had undergone a stress MRI that included both an adenosine-stress myocardial perfusion reserve and a dobutamine-stress wall-motion assessment. In multivariate analysis, they found that either abnormal myocardial reserve or stress wall motion abnormality were predictive of both cardiac death and nonfatal MI (hazard ratio = 10.57, p < 0.001; hazard ratio = 4.72, p = 0.002, respectively). Combining the results of the perfusion and wall motion evaluation was not superior to either assessment alone.
SPECT.
Mahmarian and the ASPIRE Investigators (90) also reported a landmark randomized prospective trial of intensive medical therapy versus coronary revascularization in 205 patients with sizable total and ischemic adenosine-induced defects and an ejection fraction >35%. Both intensive medical therapy and coronary revascularization produced comparable reductions in total and ischemic perfusion defect sizes on SPECT 1 year later (Fig. 6). In an accompanying editorial, Gibbons and Miller (91) outlined the barriers to the implementation of these results in current clinical practice.
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Figure 6 Effect of Medical Therapy and Revascularization on SPECT Perfusion Defects
Mean (±SD) and individual changes in total and ischemic left ventricular (LV) perfusion defect size (PDS) from initial SPECT to follow-up SPECT in patients randomized to medical therapy or revascularization. The dashed line represents 95% confidence interval for a real patient change. SPECT = single-photon emission computed tomography. Figure used with permission from Mahmarian et al. (90).
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Several studies used SPECT sestamibi to assess myocardial salvage and infarct size. In the BRAVE-2 (Beyond twelve hours Preperfusion AlternatiVe with Evaluation) trial, Parodi et al. (92) reported that primary percutaneous coronary intervention increased myocardial salvage and reduced infarct size in ST-segment elevation myocardial infarction patients presenting between 12 and 48 h after the onset of symptoms. Ali et al. (93) used infarct size by sestamibi as the primary end point in a randomized trial of rheolytic thrombectomy in 480 patients with ST-segment elevation myocardial infarction. Unfortunately, thrombectomy increased infarct size and worsened other secondary end points. In contrast to previous studies of reperfusion therapy, Kaltoft et al. (94) performed an initial sestamibi injection immediately after treatment with percutaneous coronary intervention; they demonstrated that the perfusion defect on subsequent imaging was closely correlated with final infarct size assessed on perfusion imaging three months later. Their results suggested the possible use of early myocardial perfusion imaging to identify patients with inadequate tissue level perfusion despite Thrombolysis In Myocardial Infarction flow grade 3.
Adelstein and Saba (95) reported provocative results on a selected subset of patients who underwent myocardial perfusion imaging and echocardiography before cardiac resynchronization therapy and then follow-up echocardiography. They demonstrated that several findings on baseline myocardial perfusion imaging (global infarct size, infarction near the left ventricular leads, and the extent of severely decreased perfusion) were all inversely correlated with the long-term change in ejection fraction after cardiac resynchronization therapy (Fig. 7). They suggested the need for prospective studies to confirm their results in less selected patients.
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Figure 7 SPECT Prediction of Response to Resynchronization
Summed rest score (SRS) on SPECT predicted echocardiographic response rate after cardiac resynchronization therapy. The hazard ratio for nonresponse with SRS  27 is 3.59 (95% confidence interval 1.63 to 7.91; p < 0.0001). SPECT = single-photon emission computed tomography. Figure used with permission from Adelstein and Saba (95).
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PET.
Yoshinaga et al. (79) employed rubidium-82 PET to study the effects of exercise training on myocardial blood flow in 12 patients with documented CAD and exercise-induced ischemia. They demonstrated an improvement in flow reserve, both globally and in normal segments, and an improvement in both hyperemic blood flow and flow reserve in abnormal segments. These findings may explain the clinical benefit of cardiovascular rehabilitation.
In a second article, Yoshinaga et al. (96) used cardiac PET to evaluate the effects of continuous positive airway pressure (CPAP) on myocardial efficiency. The use of CPAP did not improve myocardial efficiency after 1 h, but did have a measurable significant benefit over the course of 6 weeks. These results define a possible mechanism of the clinical benefit of CPAP in patients with obstructive sleep apnea and heart failure.
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Ventricular Function
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PET.
Two studies used FDG-PET to better define myocardial glucose metabolism. Dutka et al. (97) examined the effect of type 2 diabetes mellitus on myocardial glucose utilization in patients with CAD and heart failure. They demonstrated decreased myocardial glucose utilization and reduced extraction of glucose and suggested that myocardial insulin resistance in these patients may explain their poor long-term outcome.
Søndergaard et al. (98) studied 27 diabetic patients with CAD and normal left ventricular function to determine whether myocardial insulin resistance was present, as it is in patients with CAD, diabetes, and abnormal left ventricular function. They were unable to demonstrate insulin resistance using PET-FDG.
CT.
Several studies validated the use of CT for the measurement of left and right ventricular ejection fraction, although several of these demonstrated limitations of cardiac volume measurements (99–103).
Studies of regional wall motion using multiphase reconstruction CT angiography had variable results. Henneman et al. (104) showed good agreement between CT and SPECT and between CT and echocardiography on a per-segment basis (95% and 96%, respectively). However, Schepis et al. (105) demonstrated only moderate correlation between CT and SPECT for regional wall motion (r = 0.648). Using MRI as the reference standard, Dewey et al. (106) showed that CT was superior to biplane ventriculography for regional wall motion analysis and correlated better with MRI than echocardiography for volumetric parameters. Conversely, Fischbach et al. (107) also compared CT with MRI for regional wall motion and reported that CT underestimated the degree of motion impairment. In addition, interobserver agreement was reduced for CT as compared with MRI (67% vs. 89%, p < 0.01) (107).
Henneman et al. (108) performed an ambitious study of CTA to assess left ventricular viability, regional and global ventricular function, and coronary artery anatomy and physiology in 21 patients with known myocardial infarction. Despite the fact that this study was performed using a 16-detector row system, they found excellent correlation between CT and SPECT for regional wall motion (92%, = 0.77) and ejection fraction (r = 0.85). They found that CT also performed well in the evaluation of myocardial perfusion by first-pass enhancement, detecting 93% of perfusion defects (68 of 73) and 98% of normal segments (277 of 284) compared with SPECT (Figs. 8 and 9).
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Figure 8 CT Detection of Infarction
Midventricular short-axis CT images reconstructed in end diastole (A) and end systole (B) demonstrate characteristic findings of an inferior myocardial infarction with wall thinning and poor contractility of the inferior wall (arrow) at CT. CT = computed tomography. Figure used with permission from Henneman et al. (108).
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Figure 9 Comparison of SPECT and CT in a Patient With Infarction
Midventricular short-axis SPECT (A) and CT images (B) demonstrating corresponding inferior wall rest perfusion defect on SPECT (white arrow in A) and inferior wall hypoenhancement on CT (black arrow in B), characteristic of an inferior myocardial infarction. CT = computed tomography; SPECT = single-photon emission computed tomography. Figure used with permission from Henneman et al. (108).
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MRI.
Because of its high reproducibility, MRI has become a gold-standard for ventricular function and ventricular volumes; these are frequently used as an end point in trials. In particular, MRI is often used as end point in studies of stem cell or granulocyte colony stimulating factor treatment for acute or chronic infarction. The most recent studies on this topic are summarized in Table 8
(109–113). Tandri et al. (108) published normal values of adult right ventricular volumes, subdivided by age, gender, and ethnicity, reflecting the maturity of this field.
Magnetic resonance imaging is also capable of more detailed function measurements, such as the tracking of specific portions of the myocardium and the quantification of regional left ventricular (LV) function, often in the form of strain. Carmichael et al. (114) assessed regional function in 95 patients before and after surgical ventricular restoration surgery. Although ventricular volumes improved, regional LV function did not, which the authors interpreted as a sign of continued LV remodeling after surgery. Fernandes et al. (115) prospectively examined 500 subjects as part of the MESA study mentioned previously. They found that carotid intimal medial thickness (a measure of subclinical atherosclerosis) was associated with alterations of myocardial strain parameters, suggesting subclinical atherosclerosis with incipient myocardial dysfunction in the absence of known heart disease.
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Appropriateness
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Concern has continued over the rapid growth of cardiac imaging. Douglas et al. (116) reported the proceedings of an important think tank on quality in cardiovascular imaging, which included representatives from multiple different professional and health organizations. The proceedings considered 4 different dimensions of the imaging process—patient selection, image acquisition, image interpretation, and results communication, for a range of cardiac imaging procedures, including echocardiography, vascular ultrasound, SPECT, CT, MRI, and diagnostic angiography. The report highlights examples of quality measures and action items for four dimensions for each modality. Implementation of these action items will require a broad effort of the cardiovascular imaging community.
Two important studies (117,118) reported better patient outcomes with higher doses of beta-blockers and tighter heart rate control during noncardiac surgery. These are likely to influence future updates of the guidelines for the perioperative cardiac assessment of non-cardiac surgical patients, and ultimately the appropriateness criteria for stress SPECT.
Along with the American College of Radiology and multiple other organizations, the American College of Cardiology Foundation published a detailed set of appropriateness criteria for cardiac CT and MRI (119).
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Conclusions
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We hope that this review will encourage a broader imaging approach to clinical problems and help the reader identify articles that are of sufficient interest to merit a more detailed examination.
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Footnotes
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1 Dr. Gibbons has received a research grant from King Pharmaceuticals, which is developing an adenosine agonist for pharmacologic stress testing. 
2 Dr. Williamson is a consultant for GE Medical and has received a research grant from and is a consultant for Berlex Medical.
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References
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