Interventional Cardiovascular Magnetic Resonance Imaging: A New Opportunity for Image-Guided Interventions

Cardiovascular magnetic resonance (CMR) combines excellent soft-tissue contrast, multiplanar views, and dynamic imaging of cardiac function without ionizing radiation exposure.

Interventional cardiovascular magnetic resonance (iCMR) leverages these features to enhance conventional interventional procedures or to enable novel ones. Although still awaiting clinical deployment, this young field has tremendous potential.

We survey promising clinical applications for iCMR. Next, we discuss the technologies that allow CMR-guided interventions and, finally, what still needs to be done to bring them to the clinic.

PMID: 19909937

A Randomized Comparison of Transradial Versus Transfemoral Approach for Coronary Angiography and Angioplasty

OBJECTIVES: The aim of the study was to evaluate the safety, feasibility, and procedural variables by the transradial approach compared with the transfemoral access in a standard population of patients undergoing coronary catheterization. Coronary catheterization is usually performed via the transfemoral approach. Transradial access may offer some advantages in comparison with transfemoral access especially under conditions of aggressive anticoagulation and antiplatelet treatment.

METHODS: Between July 2006 and January 2008, a total of 1,024 patients undergoing coronary catheterization were randomly assigned to the transradial or transfemoral approach. Patients with an abnormal Allen’s test, history of coronary artery bypass surgery, simultaneous right heart catheterization, chronic renal insufficiency, or known difficulties with the radial or femoral access were excluded.

RESULTS: Successful catheterization was achieved in 494 of 512 patients (96.5%) in the transradial and in 511 of 512 patients (99.8%) in the transfemoral group (p < 0.0001). Median procedural duration (37.0 min, interquartile range [IQR] 19.6 to 49.1 min vs. 40.2 min, IQR 24.3 to 50.8 min; p = 0.046) and median dose area product (38.2 Gycm(2), IQR 20.4 to 48.5 Gycm(2) vs. 41.9 Gycm(2), IQR 22.6 to 52.2 Gycm(2); p = 0.034) were significantly lower in the transfemoral group compared with the transradial access group. A median amount of contrast agent was similar among both groups. Vascular access site complications were higher in the transfemoral group (3.71%) than in the transradial group (0.58%; p = 0.0008)

CONCLUSIONS: The findings of the present study show that transradial coronary angiography and angioplasty are safe, feasible, and effective with similar results to those of the transfemoral approach. However, procedural duration and radiation exposure are higher using the transradial access. In contrast to the transfemoral route, the rate of major vascular complications was negligible using the transradial approach.

PMID: 19926042

Image Quality of Coronary 320-MDCT in Patients with Atrial Fibrillation: Initial Experience

OBJECTIVE: Noninvasive coronary angiography has generally been contraindicated in patients with atrial fibrillation because of the difficulty in synchronizing an irregular heartbeat with table gantry movement. The objective of this study was to evaluate and compare the quality of 320-MDCT images obtained in patients with atrial fibrillation and in a control group of patients in sinus rhythm.

METHODS: Two reviewers were blinded to the patient groups and evaluated images of 15 coronary artery segments for each patient using 320-MDCT. The images were printed on glossy paper and scored subjectively as 1 or 2, meaning of diagnostic quality, or 3, meaning poor quality.

RESULTS: No statistical difference between the groups was noted in patient age: The mean age of the patients with atrial fibrillation was 67 years (age range, 52–82 years) and that of the patients in sinus rhythm was 59 years (36–86 years) (p = 0.3). Scores of 1 and 2 (diagnostic quality) were assigned to 100% in sinus rhythm and 96% in atrial fibrillation (p < 0.05). Scores of 3 were seen only in the atrial fibrillation group (7/175, 4%). Segment 15, the distal circumflex artery, was the segment that was most frequently assigned a score of 3 (2/7, 28.6%). A discrepancy in the two reviewers’ scores was seen in 25 segments (7%), requiring joint consensus. The segments that most frequently required consensus reading were segments 12 and 15. The overall mean image quality score for all three coronary arteries in atrial fibrillation was 1.25 ± 0.47 (SD) and 1.08 ± 0.26 in sinus rhythm (p < 0.001). The median effective dose was 19.28 and 13.55 mSv in the atrial fibrillation and sinus rhythm groups, respectively.

CONCLUSION: The analysis of our initial experience shows that imaging in patients with atrial fibrillation is possible using 320-MDCT, with images of most segments obtained being of diagnostic quality. Segment 15 was the most difficult to see on 320-MDCT because of the small caliber of the vessel; poor visualization of that segment mostly occurred in the setting of a dominant right coronary arterial system.

PMID: Pending

A Half Century of Selective Coronary Arteriography

The first “selective” coronary arteriogram was made 50 years ago by Dr. F. Mason Sones at the Cleveland Clinic. Soon afterward coronary arteriography was developed as a diagnostic method suitable for widespread clinical application. This method has revolutionized our understanding of coronary artery disease and has become the basis for selecting and evaluating therapeutic interventions. This viewpoint commemorates the achievements of the pioneers of coronary arteriography, the difficultiesthey encountered, and their impact on the development of  modern  cardiology. Developments during the last half century and prospects for the future are discussed in historical perspective

PMID:

Coronary Artery Calcification Screening: Estimated Radiation Dose and Cancer Risk

OBJECTIVES: Multidetector computed tomography has been proposed as a tool for routine screening for coronary artery calcification in asymptomatic individuals. As proposed, such screening could involve tens of millions of individuals, but detailed estimates of radiation doses and potential risk of radiation-induced cancer are not currently available. We estimated organ-specific radiation doses and associated cancer risks from coronary artery calcification screening with multidetector computed tomography according to patient age, frequency of screening, and scan protocol.

METHODS: Radiation doses delivered to adult patients were calculated from a range of available protocols using Monte Carlo radiation transport. Radiation risk models, derived using data from Japanese atomic bomb survivors and medically exposed cohorts, were used to estimate the excess lifetime risk of radiation-induced cancer.

RESULTS: The radiation dose from a single coronary artery calcification computed tomographic scan varied more than 10-fold (effective dose range, 0.8-10.5 mSv) depending on the protocol. In general, higher radiation doses were associated with higher x-ray tube current, higher tube potential, spiral scanning with low pitch, and retrospective gating. The wide dose variation also resulted in wide variation in estimated radiation-induced cancer risk. Assuming screening every 5 years from the age of 45 to 75 years for men and 55 to 75 years for women, the estimated excess lifetime cancer risk using the median dose of 2.3 mSv was 42 cases per 100 000 men (range, 14-200 cases) and 62 cases per 100 000 women (range, 21-300 cases).

CONCLUSIONS: These radiation risk estimates can be compared with potential benefits from screening, when such estimates are available. Doses and therefore risks can be minimized by the use of optimized protocols.

PMID: 19597067

Detection and Characteristics of Microvascular Obstruction in Reperfused Acute Myocardial Infarction using an Optimized Protocol for Contrast-Enhanced Cardiovascular Magnetic Resonance Imaging

OBJECTIVES: Several cardiovascular magnetic resonance imaging (CMR) techniques are used to detect microvascular obstruction (MVO) after acute myocardial infarction (AMI).

METHODS: To determine the prevalence of MVO and gain more insight into the dynamic changes in appearance of MVO, we studied 84 consecutive patients with a reperfused AMI on average 5 and 104 days after admission, using an optimised single breath-hold 3D inversion recovery gradient echo pulse sequence (IR-GRE) protocol.

RESULTS: Early MVO (2 min post-contrast) was detected in 53 patients (63%) and late MVO (10 min post-contrast) in 45 patients (54%; p = 0.008). The extent of MVO decreased from early to late imaging (4.3 +/- 3.2% vs. 1.8 +/- 1.8%, p < 0.001) and showed a heterogeneous pattern. At baseline, patients without MVO (early and late) had a higher left ventricular ejection fraction (LVEF) than patients with persistent late MVO (56 +/- 7% vs. 48 +/- 7%, p < 0.001) and LVEF was intermediate in patients with early MVO but late MVO disappearance (54 +/- 6%). During follow-up, LVEF improved in all three subgroups but remained intermediate in patients with late MVO disappearance.

CONCLUSIONS: This optimised single breath-hold 3D IR-GRE technique for imaging MVO early and late after contrast administration is fast, accurate and allows detection of patients with intermediate remodelling at follow-up.

PMID: 19588152

MRI and CT Appearances of Cardiac Tumours in Adults

OBJECTIVES: Primary cardiac tumours are rare, and metastases to the heart are much more frequent. Myxoma is the commonest benign primary tumour and sarcomas account for the majority of malignant lesions. Clinical manifestations are diverse, non-specific, and governed by the location, size, and aggressiveness.

METHODS: Imaging plays a central role in their evaluation, and familiarity with characteristic features is essential to generate a meaningful differential diagnosis.

RESULTS: Cardiac magnetic resonance imaging (MRI) has become the reference technique for evaluation of a suspected cardiac mass. Computed tomography (CT) provides complementary information and, with the advent of electrocardiographic gating, has become a powerful tool in its own right for cardiac morphological assessment.

CONCLUSIONS: This paper reviews the MRI and CT features of primary and secondary cardiac malignancy. Important differential considerations and potential diagnostic pitfalls are also highlighted.

PMID: 19913133

Relation Between Visceral Fat and Coronary Artery Disease Evaluated by Multidetector Computed Tomography

OBJECTIVES: Visceral abdominal fat has been associated to cardiovascular risk factors and coronary artery disease (CAD). Computed tomography (CT) coronary angiography is an emerging technology allowing detection of both obstructive and nonobstructive CAD adding information to clinical risk stratification. The aim of this study was to evaluate the association between CAD and adiposity measurements assessed clinically and by CT.

METHODS: We prospectively evaluated 125 consecutive subjects (57% men, age 56.0+/-12 years) referred to perform CT angiography. Clinical and laboratory variables were determined and CT angiography and abdominal CT were performed in a 64-slice scanner. CAD was defined as any plaque calcified or not detected by CT angiography. Visceral and subcutaneous adiposity areas were determined at different intervertebral levels.

RESULTS: CT angiography detected CAD in 70 (56%) subjects, and no association was found with usual anthropometric adiposity measurements (waist and hip circumferences and body mass index). Otherwise, CT visceral fat areas (VFA) were significantly related to CAD. VFA T12-L1 values >145cm(2) had an odds ratio of 2.85 (95% CI 1.30-6.26) and VFA L4-L5 >150cm(2) had a 2.87-fold (95% CI 1.31-6.30) CAD risk.

CONCLUSIONS: The multivariate analysis determined age and VFA T12-L1 as the only independent variables associated to CAD. Visceral fat assessed by CT is an independent marker of CAD determined by CT angiography.

PMID: 19922936

Dual source CT Coronary Angiography in Severely Obese Patients: Trading Off Temporal Resolution and Image Noise

OBJECTIVES: To assess in severely obese patients the subjective and objective image quality parameters and to estimate the radiation dose of dual-source computed tomography coronary angiography (CTCA), using 3 different protocols.

METHODS: Dual-source CTCA was performed in 60 patients (30 women; mean age 58 +/- 7 years) suffering from obesity class II or higher (body mass index [BMI] >35 kg/sq m). Twenty patients were examined with a standard CTCA protocol at 120 kV/350 mAs (protocol A), 20 patients with a CTCA protocol at 140 kV/350 mAs (protocol B), and 20 patients at 140 kV/350 mAs with a dedicated obesity protocol (protocol C), that allows the additional data sampling by expanding the data acquisition for each tube from a quarter to a half rotation, permitting to trade off temporal resolution and image noise. Two blinded observers independently assessed the image quality of each coronary segment, using a 4-point scale (1: excellent-4: nondiagnostic) and measured the different image parameters (image noise, signal-to-noise ratio [SNR], and contrast-to-noise ratio [CNR]). Radiation dose estimates were calculated.

RESULTS: The average BMI was 46.3 +/- 8.3 kg/sq m (range, 36.8-69.6 kg/sq m). Subjective image quality (1.55 +/- 0.73) was significantly better in protocol C when compared with protocol A (2.46 +/- 0.76; P < 0.01) and protocol B (2.12 +/- 0.87; P < 0.017). There was a significantly lower rate of coronary artery segments with nondiagnostic image quality when using the obesity protocol C (1.5%; 4/262) compared with that obtained when using protocol A (7.8%; 22/280; P < 0.01) and protocol B (4.4%; 12/275; P < 0.017). Image noise was significantly lower in protocol C (31.8 +/- 5.0 HU) when compared with group A (43.5 +/- 4.7 HU; P < 0.001) and B (36.8 +/- 5.5 HU; P < 0.01). SNR and CNR were significantly higher in group C (13.8 +/- 2.4 and 23.1 +/- 2.8) compared with group A (10.6 +/- 1.7 and 15.1 +/- 3.2; each P < 0.001) and group B (12.0 +/- 2.0 and 18.8 +/- 3.1; each P < 0.01). The estimated effective radiation dose of the obesity protocol C (15.6 +/- 0.9 mSv) was significantly higher when compared with that in protocol A (10.1 +/- 0.8 mSv; P < 0.01), but not significantly different from that in protocol B (13.3 +/- 0.8 mSv; P = 0.022).

CONCLUSIONS: Use of an obesity protocol in dual-source CTCA in severely obese patients significantly improves image quality, but goes along with a higher radiation dose.

PMID: 19809341

Outcomes of Patients With Acute Type A Aortic Intramural Hematoma

OBJECTIVES: The proper treatment option for patients with type A intramural hematoma (IMH), a variant form of classic aortic dissection (AD), remains controversial. We assessed the outcome of our institutional policy of urgent surgery for unstable patients and initial medical treatment for stable patients with surgery in cases with complications.

METHODS: Among 357 consecutive patients with type A acute aortic syndrome, 101 (28.3%) had IMH and 256 had AD. Urgent operations were performed in 224 patients with AD (87.5%) and 16 with unstable IMH (15.8%; P<0.001). The remaining 85 stable IMH patients received initial medical treatment, and adverse clinical events developed in 31 patients (36.5%) within 6 months, which included development of AD (n=25), delayed surgery (n=25), or death (n=6).

RESULTS: Initial aorta diameter and hematoma thickness were independent predictors for development of these events, and the best cutoff values were 55 and 16 mm, respectively. The overall hospital mortality was lower in IMH patients than in AD patients (7.9% [8/101] versus 17.2% [44/256]; P=0.0296) and was comparable to that of surgically treated AD patients (7.9% versus 10.7% [24/224]; P=0.56). The 1-, 2-, and 3-year survival rates of IMH patients were 87.6+/-3.6%, 84.9+/-3.7%, and 83.1+/-4.1%, respectively. There was no statistical difference of overall survival rates between patients with IMH and surgically treated AD patients (P=0.787).

CONCLUSIONS: The clinical outcome of IMH patients receiving treatment by our policy was comparable to that of surgically treated AD patients. However, adverse clinical events were not uncommon with medical treatment alone, and initial aorta diameter and hematoma thickness may identify patients who might benefit from urgent surgery.

PMID: 19901188

New Reconstruction Algorithm Allows Shortened Acquisition Time for Myocardial Perfusion SPECT

OBJECTIVES: : Shortening scan time and/or reducing radiation dose at maintained image quality are the main issues of the current research in radionuclide myocardial perfusion imaging (MPI). We aimed to validate a new iterative reconstruction (IR) algorithm for SPECT MPI allowing shortened acquisition time (HALF time) while maintaining image quality vs. standard full time acquisition (FULL time).

METHODS: In this study, 50 patients, referred for evaluation of known or suspected coronary artery disease by SPECT MPI using 99mTc-Tetrofosmin, underwent 1-day adenosine stress 300 MBq/rest 900 MBq protocol with standard (stress 15 min/rest 15 min FULL time) immediately followed by short emission scan (stress 9 min/rest 7 min HALF time) on a Ventri SPECT camera (GE Healthcare). FULL time scans were processed with IR, short scans were additionally processed with a recently developed software algorithm for HALF time emission scans. All reconstructions were subsequently analyzed using commercially available software (QPS/QGS, Cedars Medical Sinai) with/without X-ray based attenuation correction (AC). Uptake values (percent of maximum) were compared by regression and Bland-Altman (BA) analysis in a 20-segment model.

RESULTS: HALF scans yielded a 96% readout and 100% clinical diagnosis concordance compared to FULL. Correlation for uptake in each segment (n = 1,000) was r = 0.87at stress (p < 0.001) and r = 0.89 at rest (p < 0.001) with respective BA limits of agreement of -11% to 10% and -12% to 11%. After AC similar correlation (r = 0.82, rest; r = 0.80, stress, both p < 0.001) and BA limits were found (-12% to 10%; -13% to 12%).

CONCLUSION: With the new IR algorithm, SPECT MPI can be acquired at half of the scan time without compromising image quality, resulting in an excellent agreement with FULL time scans regarding to uptake and clinical conclusion.

PMID: 19921186

Influence of Myocardial Fibrosis on Left Ventricular Diastolic Function

OBJECTIVES: Fibrosis is a common end point of many pathological processes affecting the myocardium and may alter myocardial relaxation properties. By measuring myocardial fibrosis with cardiac magnetic resonance and diastolic function with Doppler echocardiography, we sought to define the influence of fibrosis on left ventricular diastolic function.

METHODS: Two hundred four eligible subjects from 252 consecutive subjects undergoing late postgadolinium myocardial enhancement (LGE) cardiac magnetic resonance and Doppler echocardiography were investigated.

RESULTS: Subjects with normal diastolic function exhibited no or minimal fibrosis (median LGE score, 0; interquartile range, 0 to 0). In contrast, the majority of patients with cardiomyopathy (regardless of underlying cause) had abnormal diastolic function indices and substantial fibrosis (median LGE score, 3; interquartile range, 0 to 6.25). Prevalence of LGE positivity by diastolic filling pattern was 13% in normal, 48% in impaired relaxation, 78% in pseudonormal, and 87% in restrictive filling (P<0.0001). Similarly, LGE score was significantly higher in patients with deceleration time <150 ms (P<0.012), and it progressively increased with increasing left ventricular filling pressure estimated by tissue Doppler imaging–derived E/E’ (P<0.0001). After multivariate analysis, LGE remained significantly correlated with degree of diastolic dysfunction (P=0.0001).

CONCLUSIONS: Severity of myocardial fibrosis by LGE significantly correlates with the degree of diastolic dysfunction in a broad range of cardiac conditions. Noninvasive assessment of myocardial fibrosis may provide valuable insights into the pathophysiology of left ventricular diastolic function and therapeutic response.

PMID: pending

Intracoronary Optical Coherence Tomography: A Comprehensive Review

OBJECTIVES: Cardiovascular optical coherence tomography (OCT) is a catheter-based invasive imaging system.

METHODS: Using light rather than ultrasound, OCT produces high-resolution in vivo images of coronary arteries and deployed stents. This comprehensive review will assist practicing interventional cardiologists in understanding the technical aspects of OCT based upon the physics of light and will also highlight the emerging research and clinical applications of OCT.

RESULTS: Semi-automated imaging analyses of OCT systems permit accurate measurements of luminal architecture and provide insights regarding stent apposition, overlap, neointimal thickening, and, in the case of bioabsorbable stents, information regarding the time course of stent dissolution. T

CONCLUSIONS: The advantages and limitations of this new imaging modality will be discussed with emphasis on key physical and technical aspects of intracoronary image acquisition, current applications, definitions, pitfalls, and future directions.

PMID: 19926041

Multicenter Investigation Comparing a Highly Efficient Half-Time Stress-Only Attenuation Correction Approach Against Standard Rest-Stress Tc-99m SPECT Imaging

OBJECTIVES: New iterative algorithms for scatter compensation (SC), noise suppression, and depth-dependent collimator resolution (RR) can shorten rest and stress SPECT acquisitions by 50% while maintaining quality and accuracy equivalent to conventional scans. Full-time stress-only myocardial perfusion SPECT is accurate and efficient when combined with line-source attenuation correction (LSAC). We investigated the potential for half-time stress-only LSAC-SPECT by comparing this to conventional rest/stress SPECT in patients imaged for suspected CAD at three different centers.

METHODS: One hundred and ten patients (58% men, 53% exercise) had 64 projection rest/stress Tc-99m ECG-gated SPECT with simultaneous Gd-153 LSAC: 18 had < 5% CAD likelihood and 92 had coronary angiography. The stress scans were retrospectively ‘stripped’ to create equally spaced 32 projection “half-time” (HT) scans for the emission and transmission (TX) projections. Astonish (Philips, Milpitas, CA) processing with AC, SC, and RR was applied to the HT data with the HT TX maps reconstructed using a Bayesian iterative method. The conventional rest/stress image sets processed using filtered back projection and without AC and the HT-AC stress-only images were interpreted in random sequence by consensus of two readers blinded to clinical information in separate reading sessions.

RESULTS: Comparing rest/stress FBP and HT-LSAC, stress perfusion quality was excellent/good in 82 and 89% (P = .13); interpretive certainty (definitely normal or abnormal) was 88 and 95% (P = .14); sensitivity was 77 and 83% (P = .38); specificity was 67 and 71% (P = .65); normalcy was 94 and 100% (P = 1.0); SSS for CAD pts was 7.4 vs 7.8 and for non-CAD pts was 0.7 vs 0 (P = .44 and .16, respectively). Mean stress LVEF was 60% in both groups.

CONCLUSIONS: Stress-only imaging with HT-LSAC using the Astonish acquisition/processing method provides results equivalent to conventional rest/stress scanning. This new approach has the potential to significantly improve operational efficiency without sacrificing accuracy.

PMID: 19548048

Real-Time Three-Dimensional Transoesophageal Echocardiography in the Assessment of Aortic Valve Stenosis

OBJECTIVES: To determine the feasibility of real-time three-dimensional transoesophageal echocardiography (3D-TOE) in the evaluation of aortic valve stenosis, to study its reliability, and to test the concordance of this new method when compared with transthoracic two-dimensional echocardiography (2D-TTE) as the diagnostic standard.

METHODS: Fifty-nine consecutive patients with moderate-to-severe aortic valve stenosis were assessed by means of 2D-TTE and 3D-TOE by independent blinded observers.

RESULTS: Aortic valve planimetry was possible in 94.9% of patients. Inter-observer intraclass correlation coefficients (ICC) were 0.892 (CI 95% 0.818-0.936; P < 0.001), and 0.871 (CI 95% 0.780-0.925; P < 0.001) for 2D-TTE and 3D-TOE, respectively. Bland-Altman plot showed a mean difference in aortic valve area (AVA) of 0.040 cm(2), with 2D-TTE yielding larger values than 3D-TOE. ICC of both methods was 0.724 (CI 95% 0.530-0.839; P < 0.001).

CONCLUSIONS: Assessment of AVA by means of 3D-TOE is feasible in most patients with aortic valve stenosis. Reliability of the measurement is good. However, there is some disagreement with standard 2D-TTE that needs further investigation.

PMID: 19805413