Non-contrast-enhanced MR angiography in critical limb ischemia: performance of quiescent-interval single-shot (QISS) and TSE-based subtraction techniques

Magnetic Resonance Imaging Techniques in Peripheral Arterial Disease

Significance: Peripheral arterial disease (PAD) leads to a significant burden of morbidity and impaired quality of life globally. Diabetes is a significant risk factor accelerating the development of PAD with an associated increase in the risk of chronic wounds, tissue, and limb loss. Various magnetic resonance imaging (MRI) techniques are being increasingly acknowledged as useful methods of accurately assessing PAD. Recent Advances: Conventionally utilized MRI techniques for assessing macrovascular disease have included contrast enhanced magnetic resonance angiography (MRA), noncontrast time of flight MRA, and phase contrast MRI, but have significant limitations. In recent years, novel noncontrast MRI methods assessing skeletal muscle perfusion and metabolism such as arterial spin labeling (ASL), blood-oxygen-level dependent (BOLD) imaging, and chemical exchange saturation transfer (CEST) have emerged. Critical Issues: Conventional non-MRI (such as ankle-brachial index, arterial duplex ultrasonography, and computed tomographic angiography) and MRI based modalities image the macrovasculature. The underlying mechanisms of PAD that result in clinical manifestations are, however, complex, and imaging modalities that can assess the interaction between impaired blood flow, microvascular tissue perfusion, and muscular metabolism are necessary. Future Directions: Further development and clinical validation of noncontrast MRI methods assessing skeletal muscle perfusion and metabolism, such as ASL, BOLD, CEST, intravoxel incoherent motion microperfusion, and techniques that assess plaque composition, are advancing this field. These modalities can provide useful prognostic data and help in reliable surveillance of outcomes after interventions.

Magnetic Resonance Angiography of the Arteries of the Upper and Lower Extremities

Magnetic resonance angiography (MRA) is a powerful tool for assessing upper and lower extremity artery pathologies. In addition to the classic advantages of MRA, such as the absence of radiation and iodinated contrast exposure, it can provide high temporal resolution/dynamic images of the arteries with high soft tissue contrast. Although it has a relatively lower spatial resolution than computed tomography angiography, MRA does not cause blooming artifacts in heavily calcified vessels, which is crucial in small vessel assessment. Although contrast-enhanced MRA is the most preferred technique to assess extremity vascular pathologies, recent advances in non-contrast MRA protocols provide an alternative imaging technique for patients with chronic kidney disease.

A meta-analysis of the diagnostic performance of quiescent-interval-single-shot magnetic resonance angiography in peripheral arterial disease

OBJECTIVES

To evaluate by meta-analysis the diagnostic accuracy of non-contrast quiescent-interval-single-shot (QISS) magnetic resonance angiography (MRA) in patients with peripheral arterial disease (PAD) using digital subtraction angiography (DSA) or contrast-enhanced magnetic resonance angiography (CE-MRA) as reference standard.

METHODS

This study was performed and reported according to the Preferred Reporting Items for Systematic reviews and Meta-analysis guidelines. A systematic literature search of MEDLINE, Embase and Scopus was done for studies reporting the diagnostic accuracy of QISS in PAD published up to 31 May 2021. The pooled sensitivity, specificity and diagnostic accuracy of QISS were calculated on a per-segment basis for the entire arterial tree.

RESULTS

Seventeen studies including 459 patients were found eligible for the meta-analysis. There was significant heterogeneity among studies as depicted by chi-square test (p = 0.02) and moderate heterogeneity by I² statistic (I²: 69 [95% CI: 30-100]). The pooled sensitivity and specificity of QISS on a per-segment basis with DSA/CE-MRA as reference standard was 0.88 (95% CI: 0.85-0.91) and 0.94 (95% CI: 0.92-0.96) respectively. The area under hierarchical summary receiver-operating characteristic reflected a high accuracy of 0.96 (95% CI: 0.94-0.98). There was a low likelihood of publication bias as indicated by Deeks' funnel plot.

CONCLUSIONS

The present meta-analysis has consolidated the evidence that QISS has high accuracy for identifying as well as excluding arterial stenosis/occlusions in patients with symptoms of PAD. It can thus be considered the test of choice in patients with renal failure and in "at-risk patients" including pregnant women and patients with contrast allergy.

KEY POINTS

• The pooled sensitivity and specificity of QISS magnetic resonance angiography on a per-segment basis with DSA or contrast-enhanced MRA as reference standard are 88% and 94% respectively. • The diagnostic accuracy of QISS in patients with peripheral arterial disease as reflected by area under hierarchical summary receiver-operating characteristic is high (0.96 (95% CI: 0.94-0.98)). • There is moderate to significant heterogeneity among studies as depicted by I² statistic and chi-square test.

Quantification of popliteal artery narrowing with QISS MRA during active ankle plantarflexion in healthy, asymptomatic volunteers and its potential application in the diagnosis of popliteal artery entrapment syndrome (PAES)

OBJECTIVE

To assess the degree of narrowing of the popliteal artery during active ankle plantar flexion in healthy volunteers using a non-contrast quiescent-interval single-shot (QISS) magnetic resonance angiography (MRA) technique.

MATERIALS AND METHODS

Following IRB approval, 10 healthy volunteers were recruited and following informed consent underwent QISS MRA of the lower extremity at rest and during ankle plantarflexion. Two pediatric musculoskeletal radiologists independently reviewed MR images in random order and recorded a number of subjective and objective anatomic variables including branch pattern, proximity of vessel to bony structures, gastrocnemius bulk, and presence of accessory muscle. Arterial narrowing with plantarflexion was recorded by a subjective assessment of 3D reconstructions (negligible or non-negligible) and objectively by measuring the narrowest diameter during plantarflexion and at rest. Agreement between reader scores was assessed using the concordance correlation coefficient (CCC) for continuous variables, and kappa and the proportion of agreement for categorical variables.

RESULTS

Mean reduction in arterial diameter during plantar flexion was 17.1% (min 1.9%, max 64.1%, SD 16.7%) for reader 1 and 17.2% (min 1.7%, max 50.0%, SD 14.3%.) for reader 2 with high agreement between readers: CCC = 0.92 and CI = 0.82, 0.96. Arterial narrowing was described subjectively as "non-negligible" in 7/20 legs by reader 1 and 5/20 legs by reader 2 with proportion of agreement = 0.90, CI (0.77, 1.00).

CONCLUSION

We observed a wide range of popliteal arterial narrowing with plantarflexion in asymptomatic volunteers. Larger studies, for which QISS is well suited, may be invaluable for distinguishing physiologic from pathologic arterial narrowing in patients with suspected popliteal artery entrapment syndrome (PAES).

Using Non-Contrast MRA to Discriminate between Obstructive and Nonobstructive Venous Diseases of the Legs

BACKGROUND

Venous interventions of the legs are less predictable owing to a lock of objective tools.

METHODS

One hundred and twenty patients with lower extremity venous disease were evaluated anatomically using TRANCE MRI. Then, a QFlow analysis was performed in 53 patients with only one leg affected for hemodynamic evaluation. Those patients with complete QFlow were classified into obstructive and nonobstructive.

RESULTS

The QFlow-namely, stroke volume, forward flow volume, mean flux, stroke distance (SD), and mean velocity (MV) in the external iliac vein (EIV), femoral vein (FV), popliteal vein (PV), and great saphenous vein (GSV). The obstructed group had a shorter SD and lower MV in the EIV, EIV/FV, and GSV/PV (SD: p-values of 0.025, 0.05, and 0.043, respectively; MV: p-values of 0.02, 0.05, and 0.048, respectively). A good performance in discriminating obstructive venous disease was reported for SD in the EIV (area under the curve (AUC) = 67.9%, 95% confidence interval (CI) = 53.2-82.7%), EIV/FV (AUC = 72.4%, 95% CI = 58.2-86.5%), and GSV/PV (AUC = 67.9%, 95% CI = 51.7-84.1%). The SD in the EIV, EIV/FV, and GSV/PV had the ability to discriminate between obstructive and nonobstructive diseases (p-values of 0.025, 0.005, and 0.043). The MV in the EIV, EIV/FV, and GSV/PV had ability to discriminate between obstructive and nonobstructive venous diseases (p-values of 0.02, 0.005, and 0.048).

CONCLUSIONS

The SD and MV were lower for obstructive than nonobstructive disease in the EIV.

Superficial Venous Reflux Intervention Guided by Triggered Angiography Non-Contrast-Enhanced Sequence Magnetic Resonance Imaging: Different QFlow Pattern from Health Controls

(1) Background: To assess the effectiveness of triggered angiography non-contrast-enhanced (TRANCE)-magnetic resonance imaging (MRI) in superficial venous reflux and its difference from health controls. (2) Methods: Thirty patients underwent TRANCE MRI before surgical intervention of their superficial venous reflux of the legs. Ten healthy volunteers were included as a control. (3) Results: TRANCE MRI involves the major tributaries, thus enhances the additional ablations in 20% of patients. QFlow pattern of superficial venous reflux (QFlow GSV/PV MF ratio > 1) was compared with the duplex scan (SFJ reflux) using Cohen’s kappa coefficient at 0.967. The 30 morbid legs undergoing TRANCE MRI-guide interventions and the healthy volunteers’ legs on the same side were compared. The stroke volumes (SV) are higher in EIV (p = 0.021) in the left-leg-intervention group. The mean flux (MF) is higher in the EIV (p = 0.012) and trend of increasing in GSV segment (p = 0.087) in the left-leg-intervention group. The QFlow of 10 patients with right leg intervention are higher in GSV in the right-leg-intervention group (SV p = 0.002; FFV p = 0.001; MF p = 0.001). QFlow data is shown for all legs for superficial venous intervention with GSV/PV (MF) ratio > 1. (4) Conclusions: Typical figures in QFlow (GSV/PV MF ratio > 1) could be observed in the morbid limbs but not in the controls.

Quiescent-Interval Slice-Selective MRA Accurately Estimates Intravascular Stent Dimensions Prior to Intervention in Patients With Peripheral Artery Disease

BACKGROUND

Quiescent-interval slice-selective (QISS) magnetic resonance angiography (MRA) is a non-contrast alternative for the pre-procedural assessment of patients with peripheral artery disease (PAD). However, the feasibility of pre-procedural stent size estimation using QISS MRA would merit investigation.

PURPOSE

To evaluate the feasibility of QISS MRA for pre-procedural stent size estimation in PAD patients compared to computed tomography angiography (CTA).

STUDY TYPE

Retrospective.

SUBJECTS

Thirty-three PAD patients (68 ± 9 years, 18 men, 15 women).

FIELD STRENGTH/SEQUENCE

Two-dimensional balanced steady-state free precession QISS MRA at 1.5 T and 3 T.

ASSESSMENT

All patients received QISS MRA and CTA of the lower extremity run-off followed by interventional digital subtraction angiography (DSA). Stenotic lesion length and diameter were quantified (AMF and AVS with 3 and 13 years of experience in cardiovascular imaging, respectively) to estimate the dimensions of the stent necessary to restore blood flow in the treated arteries. Measured dimensions were adjusted to the closest stent size available.

STATISTICAL TESTS

The Friedman test with subsequent pairwise Wilcoxon signed-rank test was used to compare the estimated stent dimensions between QISS MRA, CTA, and the physical stent size used for intervention. Intra-class correlation (ICC) analysis was performed to assess inter-reader agreement. Significant differences were considered at P < 0.05.

RESULTS

No significant difference was observed between estimated stent diameter by QISS MRA or CTA compared to physical stent diameter (8.9 ± 2.9 mm, 8.8 ± 3.0 mm, and 8.8 ± 3.8 mm, respectively; χ²  = 1.45, P = 0.483). There was a significant underestimation of stent length for both QISS MRA and CTA, compared to physical stent length (45.8 ± 27.8 mm, 46.4 ± 29.3 mm, and 50.4 ± 34.0 mm, respectively; χ²  = 11.96) which could be corrected when measurements were adjusted to the next available stent length (χ²  = 2.38, P = 0.303). Inter-reader assessment showed good to excellent agreement between the readers (all ICC ≥0.81).

DATA CONCLUSION

QISS MRA represents a reliable method for pre-procedural lesion assessment and stent diameter and length estimation in PAD patients.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY: Stage 2.

Discriminating Reflux from Non-Reflux Diseases of Superficial Veins in Legs by Novel Non-Contrast MR with QFlow Technique

Objectives: To find an objective diagnostic tool for the superficial veins in legs. Methods: This study included 137 patients who underwent TRANCE-MRI from 2017 to 2020 (IRB: 202001570B0). Among them, 53 with unilateral leg venous diseases underwent a QFlow scan and were classified into the reflux and non-reflux groups according to the status of the great saphenous veins. Results: The QFlow, namely stroke volume (SV), forward flow volume (FFV), mean flux (MF), stroke distance (SD), and mean velocity (MV) measured in the external iliac, femoral, popliteal, and great saphenous vein (GSV). The SV, FFV, SD, MF, SD, and MV in the GSV (morbid/non-morbid limbs) demonstrated a favorable ability to discriminate reflux from non-reflux in the ROC curve. The SD in the GSV and GSV/PV ratio (p = 0.049 and 0.047/cutoff = 86 and 117.1) and the MV in the EIV/FV ratio, GSV, and GSV/PV ratio (p = 0.035, 0.034, and 0.025/cutoff = 100.9, 86.1, and 122.9) exhibited the ability to discriminate between reflux and non-reflux group. The SD, MV, and FFV have better ability to discriminate a reflux from non-reflux group than the SV and MF. Conclusions: QFlow may be used to verify the reflux of superficial veins in the legs. An increasing GSV/PV ratio is a hallmark of reflux of superficial veins in the legs.

Highly accelerated subtractive femoral non-contrast-enhanced MRA using compressed sensing with k-space subtraction, phase and intensity correction

PURPOSE

To develop an improved reconstruction method, k-space subtraction with phase and intensity correction (KSPIC), for highly accelerated, subtractive, non-contrast-enhanced MRA.

METHODS

The KSPIC method is based on k-space subtraction of complex raw data. It applies a phase-correction procedure to restore the polarity of negative signals caused by subtraction and an intensity-correction procedure to improve background suppression and thereby sparsity. Ten retrospectively undersampled data sets and 10 groups of prospectively undersampled data sets were acquired in 12 healthy volunteers. The performance of KSPIC was compared with another improved reconstruction based on combined magnitude subtraction, as well as with conventional k-space subtraction reconstruction and magnitude subtraction reconstruction, both using quantitative metrics and using subjective quality scoring.

RESULTS

In the quantitative evaluation, KSPIC had the best performance in terms of peak SNR, structural similarity index measure, contrast-to-noise ratio of artery-to-background and sharpness, especially at high acceleration factors. The KSPIC method also had the highest subjective scores for all acceleration factors in terms of vessel delineation, image noise and artifact, and background contamination. The acquisition can be accelerated by a factor of 20 without significant decreases of subjective scores. The optimal size of the phase-correction region was found to be 12-20 pixels in this study.

CONCLUSION

Compared with combined magnitude subtraction and conventional reconstructions, KSPIC has the best performance in all of the quantitative and qualitative measurements, permitting good image quality to be maintained up to higher accelerations. The KSPIC method has the potential to further reduce the acquisition time of subtractive MRA for clinical examinations.

Noncontrast Magnetic Resonance Angiography in the Era of Nephrogenic Systemic Fibrosis and Gadolinium Deposition

ABSTRACT

Gadolinium-based contrast agents for clinical magnetic resonance imaging are overall safe. However, the discovery of nephrogenic systemic fibrosis in patients with severe renal impairment and gadolinium deposition in patients receiving contrast have generated developments in contrast-free imaging of the vasculature, that is, noncontrast magnetic resonance angiography. This article presents an update on noncontrast magnetic resonance angiography techniques, with comparison to other imaging alternatives. Potential benefits and challenges to implementation, and evidence to date for various clinical applications are discussed.

Quiescent-Interval Slice Selective Magnetic Resonance Angiography for Abdominal Aortic Aneurysm Treatment Planning

PURPOSE

Diagnostic imaging of Abdominal aortic aneurysm (AAA) almost exclusively employs CT angiography (CTA) involving X-ray exposure and contrast medium that may harm some patients. Quiescent-Interval Slice Selective MR (QISS-MR) depicts vascular anatomy without radiation or contrast medium. The diagnostic quality of QISS-MRA and CTA were compared in regard to length and diameter measurements in AAA patients. Suitability of QISS-MRA for AAA treatment planning was evaluated.

MATERIALS AND METHODS

The details of 30 patients with AAA who received both a QISS-MR and CTA for a known infrarenal AAA were obtained retrospectively that was approved by the local research ethics board. Two observers analyzed each dataset in terms of image quality and determined lumen diameter and length of 15 vessel segments.

RESULTS

Highly accurate agreement between the diagnostic scores from the two observers was achieved. There was no significant difference between CTA and QISS-MRA for all 15 measured vessels. Although information on calcification was lacking and intraluminal thrombus was visualized in only 25 patients out of 30 patients, a founded decision to carry out OR or EVAR was possible with both imaging modalities.

CONCLUSION

QISS-MRA presents a radiation and contrast free method for preoperative diagnostic AAA imaging. While QISS-MRA does not deliver exact information regarding calcification and thrombus formation, it does accurately allow measurement of vessel diameter and length. Therefore, it is potentially useful for EVAR planning in selected patients with impaired renal function.

Non-contrast-enhanced MR-angiography (MRA) of lower extremity peripheral arterial disease at 3 tesla: Examination time and diagnostic performance of 2D quiescent-interval single-shot MRA vs. 3D fast spin-Echo MRA

PURPOSE

Non-contrast enhanced MRA is a promising diagnostic alternative to contrast-enhanced (CE-) MRA or CT in patients with lower extremity peripheral arterial disease (PAD) but potentially associated with prolonged examination times and inferior diagnostic performance. We aimed to compare examination times and diagnostic performance of non-contrast enhanced quiescent-interval slice-selective (QISS)-MRA and fast-spin-echo (FSE)-MRA at 3.0 T.

MATERIALS AND METHODS

Forty-five patients with PAD were recruited for this IRB approved prospective study. Subjects underwent lower extremity MRA with 1) QISS-MRA, 2) FSE-MRA, and 3) CE-MRA (continuous table movement MRA and time-resolved MRA of the calf), which served as the standard of reference. Scan times for each examination step and total examination times for each of the three techniques was determined. Image quality and degree of stenosis were rated by two readers on a 5-point Likert scale. Sensitivity, specificity and diagnostic accuracy for relevant (>50%) stenosis were calculated.

RESULTS

Median total examination time was 27:02 min for QISS-MRA (IQR, 25:13-31:01 min), 28:37 min for FSE-MRA (IQR, 25:51-33:12 min), and 31:22 min for CE-MRA (IQR, 26:41-33:23 min). Acquisition time for QISS-MRA was significantly longer compared to FSE-MRA and CE-MRA (p ≤ 0.0001), while time for localizers, scouts and planning of the MRA sequence was significantly shorter for QISS-MRA compared to FSE-MRA and CE-MRA (p ≤ 0.0001). QISS-MRA had significantly better image quality compared to FSE-MRA with less segments classified as non-diagnostic (Reader 1: 3% vs. 35%; Reader 2: 3% vs. 50%, p ≤ 0.0001). Overall, QISS-MRA showed significantly better diagnostic performance than FSE-MRA (sensitivity, 85% vs. 54%; specificity, 90% vs. 47%, diagnostic accuracy, 89% vs. 48%; p ≤ 0.0001).

CONCLUSION

Total examination time of QISS-MRA and FSE-MRA was comparable with a conventional CE-MRA protocol. QISS-MRA showed significantly higher diagnostic performance than FSE-MRA.

Diagnostic accuracy of non-contrast quiescent-interval slice-selective (QISS) MRA combined with MRI-based vascular calcification visualization for the assessment of arterial stenosis in patients with lower extremity peripheral artery disease

OBJECTIVES

The proton density-weighted, in-phase stack-of-stars (PDIP-SOS) MRI technique provides calcification visualization in peripheral artery disease (PAD). This study sought to investigate the diagnostic accuracy of a combined non-contrast quiescent-interval slice-selective (QISS) MRA and PDIP-SOS MRI protocol for the detection of PAD, in comparison with CTA and digital subtraction angiography (DSA).

METHODS

Twenty-six prospectively enrolled PAD patients (70 ± 8 years) underwent lower extremity CTA and 1.5-T or 3-T PDIP-SOS/QISS MRI prior to DSA. Two readers rated image quality and graded stenosis (≥ 50%) on QISS MRA without/with calcification visualization. Sensitivity, specificity, and area under the curve (AUC) were calculated against DSA. Calcification was quantified and compared between MRI and non-contrast CT (NCCT) using paired t test, Pearson's correlation, and Bland-Altman analysis.

RESULTS

Image quality ratings were significantly higher for CTA compared to those for MRA (4.0 [3.0-4.0] and 3.0 [3.0-4.0]; p = 0.0369). The sensitivity and specificity of QISS MRA, QISS MRA with PDIP-SOS, and CTA for ≥ 50% stenosis detection were 85.4%, 92.2%, and 90.2%, and 90.3%, 93.2%, and 94.2%, respectively, while AUCs were 0.879, 0.928, and 0.923, respectively. A significant increase in AUC was observed when PDIP-SOS was added to the MRA protocol (p = 0.0266). Quantification of calcification showed significant differences between PDIP-SOS and NCCT (80.6 ± 31.2 mm³ vs. 88.0 ± 29.8 mm³; p = 0.0002) with high correlation (r = 0.77, p < 0.0001) and moderate mean of differences (- 7.4 mm³).

CONCLUSION

QISS MRA combined with PDIP-SOS MRI provides improved, CTA equivalent, accuracy for the detection of PAD, although its image quality remains inferior to CTA.

KEY POINTS

• Agreement in stenosis detection rate using non-contrast quiescent-interval slice-selective MRA compared to DSA improved when calcification visualization was provided to the readers. • An increase was observed in both sensitivity and specificity for the detection of ≥ 50% stenosis when MRI-based calcification assessment was added to the protocol, resulting in a diagnostic accuracy more comparable to CTA. • Quantification of calcification showed statistical difference between MRI and non-contrast CT; however, a high correlation was observed between the techniques.

"Push-button" noncontrast MR angiography using balanced T1 relaxation-enhanced steady-state (bT1RESS)

PURPOSE

We introduce a MR imaging technique, balanced T₁ relaxation-enhanced steady-state (bT1RESS), that provides the unique capability to efficiently impart a flexible amount of T₁ weighting to a balanced steady-state free precession acquisition using periodically applied contrast-modifying RF pulses. Leveraging this capability to suppress the signal intensity of background tissues, we implemented a 3D noncontrast MR angiography technique that continuously acquires thin overlapping 3D volumes and tested it for evaluation of the peripheral arteries.

METHODS

bT1RESS used a fast interrupted steady-state readout with a 45° cslab-selective ontrast-modifying RF pulse applied at 262 msec intervals. A series of 16.4-mm thick overlapping 3D volumes was acquired using a radial stack-of-stars k-space trajectory. The combination of slice oversampling, slab overlap, and averaging of edge slices was helpful to reduce venetian blind artifact. Spatial resolution was near isotropic with reconstructed slice thickness = 0.7 mm and in-plane resolution = 0.5 mm.

RESULTS

Pilot studies in the peripheral arteries demonstrated improved vessel sharpness compared with cardiac-gated quiescent interval slice-selective noncontrast MR angiography. bT1RESS noncontrast MR angiography reliably identified stenotic and occlusive arterial disease in a small cohort of patients with peripheral artery disease.

CONCLUSIONS

bT1RESS provides the basis for a simplified, completely "push button" approach for noncontrast MR angiography that obviates the need for contrast agents, electrocardiographic gating, scout imaging, breath holding, or tailoring of imaging parameters for the individual patient. Further work is needed for technical optimization and clinical validation.

Non-contrast MRI protocol for TAVI guidance: quiescent-interval single-shot angiography in comparison with contrast-enhanced CT

Objectives

To prospectively compare unenhanced quiescent-interval single-shot MR angiography (QISS-MRA) with contrast-enhanced computed tomography angiography (CTA) for contrast-free guidance in transcatheter aortic valve intervention (TAVI).

Methods

Twenty-six patients (mean age 83 ± 5 years, 15 female [58%]) referred for TAVI evaluation underwent QISS-MRA for aortoiliofemoral access guidance and non-contrast three-dimensional (3D) “whole heart” MRI for prosthesis sizing on a 1.5-T system. Contrast-enhanced CTA was performed as imaging gold standard for TAVI planning. Image quality was assessed by a 4-point Likert scale; continuous MRA and CTA measurements were compared with regression and Bland-Altman analyses.

Results

QISS-MRA and CTA-based measurements of aortoiliofemoral vessel diameters correlated moderately to very strong (r = 0.572 to 0.851, all p ≤ 0.002) with good to excellent inter-observer reliability (intra-class correlation coefficient (ICC) = 0.862 to 0.999, all p < 0.0001) regarding QISS assessment. Mean diameters of the infrarenal aorta and iliofemoral vessels differed significantly (bias 0.37 to 0.98 mm, p = 0.041 to < 0.0001) between the two modalities. However, inter-method decision for transfemoral access route was comparable (κ = 0.866, p < 0.0001). Aortic root parameters assessed by 3D whole heart MRI strongly correlated (r = 0.679 to 0.887, all p ≤ 0.0001) to CTA measurements.

Conclusion

QISS-MRA provides contrast-free access route evaluation in TAVI patients with moderate to strong correlations compared with CTA and substantial inter-observer agreement. Despite some significant differences in minimal vessel diameters, inter-method agreement for transfemoral accessibility is strong. Combination with 3D whole heart MRI facilitates unenhanced TAVI guidance.

Key Points

• QISS-MRA and CTA inter-method agreement for transfemoral approach is strong.

• QISS-MRA is a very good alternative to CTA and MRA especially in patients with Kidney Disease Outcomes Quality Initiativestages 4 and 5.

• Combination of QISS-MRA and 3D “whole heart” MRI facilitates fully unenhanced TAVI guidance.

Global Vascular Guidelines on the Management of Chronic Limb-Threatening Ischemia

GUIDELINE SUMMARY

Chronic limb-threatening ischemia (CLTI) is associated with mortality, amputation, and impaired quality of life. These Global Vascular Guidelines (GVG) are focused on definition, evaluation, and management of CLTI with the goals of improving evidence-based care and highlighting critical research needs. The term CLTI is preferred over critical limb ischemia, as the latter implies threshold values of impaired perfusion rather than a continuum. CLTI is a clinical syndrome defined by the presence of peripheral artery disease (PAD) in combination with rest pain, gangrene, or a lower limb ulceration >2 weeks duration. Venous, traumatic, embolic, and nonatherosclerotic etiologies are excluded. All patients with suspected CLTI should be referred urgently to a vascular specialist. Accurately staging the severity of limb threat is fundamental, and the Society for Vascular Surgery Threatened Limb Classification system, based on grading of Wounds, Ischemia, and foot Infection (WIfI) is endorsed. Objective hemodynamic testing, including toe pressures as the preferred measure, is required to assess CLTI. Evidence-based revascularization (EBR) hinges on three independent axes: Patient risk, Limb severity, and ANatomic complexity (PLAN). Average-risk and high-risk patients are defined by estimated procedural and 2-year all-cause mortality. The GVG proposes a new Global Anatomic Staging System (GLASS), which involves defining a preferred target artery path (TAP) and then estimating limb-based patency (LBP), resulting in three stages of complexity for intervention. The optimal revascularization strategy is also influenced by the availability of autogenous vein for open bypass surgery. Recommendations for EBR are based on best available data, pending level 1 evidence from ongoing trials. Vein bypass may be preferred for average-risk patients with advanced limb threat and high complexity disease, while those with less complex anatomy, intermediate severity limb threat, or high patient risk may be favored for endovascular intervention. All patients with CLTI should be afforded best medical therapy including the use of antithrombotic, lipid-lowering, antihypertensive, and glycemic control agents, as well as counseling on smoking cessation, diet, exercise, and preventive foot care. Following EBR, long-term limb surveillance is advised. The effectiveness of nonrevascularization therapies (eg, spinal stimulation, pneumatic compression, prostanoids, and hyperbaric oxygen) has not been established. Regenerative medicine approaches (eg, cell, gene therapies) for CLTI should be restricted to rigorously conducted randomizsed clinical trials. The GVG promotes standardization of study designs and end points for clinical trials in CLTI. The importance of multidisciplinary teams and centers of excellence for amputation prevention is stressed as a key health system initiative.

Global vascular guidelines on the management of chronic limb-threatening ischemia

Chronic limb-threatening ischemia (CLTI) is associated with mortality, amputation, and impaired quality of life. These Global Vascular Guidelines (GVG) are focused on definition, evaluation, and management of CLTI with the goals of improving evidence-based care and highlighting critical research needs. The term CLTI is preferred over critical limb ischemia, as the latter implies threshold values of impaired perfusion rather than a continuum. CLTI is a clinical syndrome defined by the presence of peripheral artery disease (PAD) in combination with rest pain, gangrene, or a lower limb ulceration >2 weeks duration. Venous, traumatic, embolic, and nonatherosclerotic etiologies are excluded. All patients with suspected CLTI should be referred urgently to a vascular specialist. Accurately staging the severity of limb threat is fundamental, and the Society for Vascular Surgery Threatened Limb Classification system, based on grading of Wounds, Ischemia, and foot Infection (WIfI) is endorsed. Objective hemodynamic testing, including toe pressures as the preferred measure, is required to assess CLTI. Evidence-based revascularization (EBR) hinges on three independent axes: Patient risk, Limb severity, and ANatomic complexity (PLAN). Average-risk and high-risk patients are defined by estimated procedural and 2-year all-cause mortality. The GVG proposes a new Global Anatomic Staging System (GLASS), which involves defining a preferred target artery path (TAP) and then estimating limb-based patency (LBP), resulting in three stages of complexity for intervention. The optimal revascularization strategy is also influenced by the availability of autogenous vein for open bypass surgery. Recommendations for EBR are based on best available data, pending level 1 evidence from ongoing trials. Vein bypass may be preferred for average-risk patients with advanced limb threat and high complexity disease, while those with less complex anatomy, intermediate severity limb threat, or high patient risk may be favored for endovascular intervention. All patients with CLTI should be afforded best medical therapy including the use of antithrombotic, lipid-lowering, antihypertensive, and glycemic control agents, as well as counseling on smoking cessation, diet, exercise, and preventive foot care. Following EBR, long-term limb surveillance is advised. The effectiveness of nonrevascularization therapies (eg, spinal stimulation, pneumatic compression, prostanoids, and hyperbaric oxygen) has not been established. Regenerative medicine approaches (eg, cell, gene therapies) for CLTI should be restricted to rigorously conducted randomizsed clinical trials. The GVG promotes standardization of study designs and end points for clinical trials in CLTI. The importance of multidisciplinary teams and centers of excellence for amputation prevention is stressed as a key health system initiative.

Noncontrast MR angiography: An update

Both computed tomography (CT) angiography (CTA) and contrast-enhanced MR angiography (CEMRA) have proven to be useful and accurate cross-sectional imaging modalities over a wide range of vascular territories and vascular disorders. A key advantage of MRA is that, unlike CTA, it can be performed without the administration of a contrast agent. In this review article we consider the motivations for using noncontrast MRA, potential contrast mechanisms, imaging techniques, advantages, and drawbacks with respect to CTA and CEMRA, and the level of evidence for using the various MRA techniques. In addition, we explore new developments that promise to expand the reliability and range of clinical applications for noncontrast MRA, along with functional MRA capabilities not available with CTA or CEMRA. Level of Evidence: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:355-373.

Evaluation of Quiescent-Interval Single-Shot Magnetic Resonance Angiography in Diabetic Patients With Critical Limb Ischemia Undergoing Digital Subtraction Angiography: Comparison With Contrast-Enhanced Magnetic Resonance Angiography With Calf Compression at 3.0 Tesla

PURPOSE

To assess the diagnostic performance of quiescent-interval single-shot magnetic resonance angiography (QISS-MRA) at 3 tesla in diabetic patients with critical limb ischemia (CLI) vs contrast-enhanced MR angiography (CE-MRA) using digital subtraction angiography (DSA) as the standard of reference.

METHOD

Thirty-seven consecutive diabetic patients (mean age 71.8±7.2 years; 30 men) with CLI (Fontaine stage III-IV) underwent QISS-MRA and CE-MRA with calf compression; DSA was the standard. Image quality (5-point Likert-type scale) and stenosis severity (5-point grading) for QISS-MRA and CE-MRA were evaluated by 2 blinded readers in 1147 and 654 vessel segments, respectively. Per-segment and per-region (pelvis, thigh, calf) sensitivity, specificity, positive predictive value, and negative predictive value were calculated.

RESULTS

Image quality of QISS-MRA was lower compared with CE-MRA in the pelvic region (p<0.001 in both readers) and thigh region (p=0.033 in reader 1 and p=0.018 in reader 2), whereas in the calf region, the image quality of QISS-MRA was better than CE-MRA (p=0.009 in reader 1 and p=0.001 in reader 2). In segment-based analyses, there was no difference between QISS-MRA and CE-MRA in sensitivity [89.5% vs 90.3% in reader 1 (p=0.774) and 87.6% vs 90.6% in reader 2 (p=0.266)] or specificity [94.2% vs 92.9% in reader 1 (p=0.513) and 92.9% vs 92.9% in reader 2 (p>0.999)]. In region-based analyses, QISS-MRA and CE-MRA yielded similar sensitivity and specificity in all areas but the pelvic region for reader 2 (specificity 95.5% vs 84.8%, p=0.041).

CONCLUSION

QISS-MRA performed very well in diabetic patients with CLI and was a good alternative for patients with contraindications to CE-MRA.

Quiescent-Interval Single-Shot Magnetic Resonance Angiography

Lower extremity peripheral arterial disease (PAD) is a chronic, debilitating disease with a significant global burden. A number of diagnostic imaging techniques exist, including computed tomography angiography (CTA) and contrast-enhanced magnetic resonance angiography (CEMRA), to aid in PAD diagnosis and subsequent treatment planning. Due to concerns of renal toxicity or nephrogenic systemic fibrosis (NSF) for iodinated and gadolinium-based contrasts, respectively, a number of non-enhanced MRA (NEMRA) protocols are being increasingly used in PAD diagnosis. These techniques, including time of flight and phase contrast MRA, have previously demonstrated poor image quality, long acquisition times, and/or susceptibility to artifacts when compared to existing contrast-enhanced techniques. In recent years, Quiescent-Interval Single-Shot (QISS) MRA has been developed to overcome these limitations in NEMRA methods, with promising results. Here, we review the various screening and diagnostic tests currently used for PAD. The various NEMRA protocols are discussed, followed by a comprehensive review of the literature on QISS MRA to date. A particular emphasis is placed on QISS MRA feasibility studies and studies comparing the diagnostic accuracy and image quality of QISS MRA versus other diagnostic imaging techniques in PAD.

Computed tomography angiography evaluation of acute limb ischemia

Acute limb ischemia (ALI), a subclass of critical limb ischemia, is a medical emergency. The cause of ALI is usually thrombotic or embolic in nature, and the specific etiology often dictates the appropriate therapy. While the diagnosis is a clinical with common presenting symptoms, advances in ultrasound, computed tomography, and magnetic resonance technology have impacted the diagnosis and subsequent therapy. In ALI, the time to revascularization is critical and computed tomography angiography (CTA) provides a highly sensitive and specific technique for rapidly identifying occlusions and precisely defining vascular anatomy prior to interventions. In patients with significant renal disease, magnetic resonance angiography with or without contrast provides effective alternatives at the expense of imaging time. Treatment can include a variety of endovascular or surgical interventions, including thromboembolectomy, angioplasty, or bypass. Proper evaluation of the etiology of the ischemia, affected vasculature, and medical history is critical to select appropriate treatment and improve patient outcomes. Here, we examine the presentation, evaluation, and treatment of ALI and the role of CTA in diagnosis and therapy.

Advances in non-contrast quiescent-interval slice-selective (QISS) magnetic resonance angiography

There is a pressing clinical need to develop accurate, efficient non-contrast magnetic resonance angiography (NC-MRA) techniques. Our efforts in the field have focused on a novel non-subtractive technique called quiescent-interval slice-selective (QISS) MRA. Compared with other NC-MRA techniques, QISS has the advantage of being more accurate while enabling a simpler and more efficient workflow. The original implementation, which uses electrocardiogram (ECG) gating and a Cartesian k-space trajectory, is a reliable technique for the evaluation of peripheral arterial disease (PAD). Recent advances in QISS technology include the use of a radial k-space trajectory, which facilitates rapid imaging of the coronary, renal, and pulmonary arteries as well as other vascular beds, and ungated ("UnQISS") acquisitions for PAD.