Iodine contrast iso-attenuating with diagnostic gadolinium doses in CTA and angiography results in ultra-low iodine doses. A way to avoid both CIN and NSF in azotemic patients?

Waiting times between examinations with intravascularly administered contrast media: a review of contrast media pharmacokinetics and updated ESUR Contrast Media Safety Committee guidelines

The pharmacokinetics of contrast media (CM) will determine how long safe waiting intervals between successive CT or MRI examinations should be. The Contrast Media Safety Committee has reviewed the data on pharmacokinetics of contrast media to suggest safe waiting intervals between successive contrast-enhanced imaging studies in relation to the renal function of the patient. CLINICAL RELEVANCE STATEMENT: Consider a waiting time between elective contrast-enhanced CT and (coronary) angiography with successive iodine-based contrast media administrations in patients with normal renal function (eGFR > 60 mL/min/1.73 m2) of optimally 12 h (near complete clearance of the previously administered iodine-based contrast media) and minimally 4 h (if clinical indication requires rapid follow-up). KEY POINTS: • Pharmacokinetics of contrast media will guide safe waiting times between successive administrations. • Safe waiting times increase with increasing renal insufficiency. • Iodine-based contrast media influence MRI signal intensities and gadolinium-based contrast agents influence CT attenuation.

Accuracy of iodine quantification using dual-energy computed tomography with focus on low concentrations

BACKGROUND

Iodine quantification using dual-energy computed tomography (DECT) is helpful in characterizing, and follow-up after treatment of tumors. Some malignant masses, for instance papillary renal cell carcinomas (p-RCC), are hard to differentiate from benign lesions because of very low contrast enhancement. In these cases, iodine concentrations might be very low, and it is therefore important that iodine quantification is reliable even at low concentrations if this technique is used.

PURPOSE

To examine the accuracy of iodine quantification and to determine whether it is also accurate for low iodine concentrations.

MATERIAL AND METHODS

Twenty-six syringes with different iodine concentrations (0-30 mg I/mL) were scanned in a phantom model using a DECT scanner with two different kilovoltage and image reconstruction settings. Iodine concentrations were measured and compared to known concentration. Absolute and relative errors were calculated.

RESULTS

For concentrations of 1 mg I/mL or higher, there was an excellent correlation between true and measured iodine concentrations for all settings (R = 0.999-1.000; P < 0.001). For concentrations <1.0 mg I/mL, the relative error was greater. Absolute and relative errors were smaller using tube voltages of 80/Sn140 kV than 100/Sn140 kV (P < 0.01). Reconstructions using a 3.0-mm slice thickness had less variance between repeated acquisitions versus 0.6 mm (P < 0.001).

CONCLUSION

Iodine quantification using DECT was in general very accurate, but for concentrations < 1.0 mg I/mL the technique was less reliable. Using a tube voltage with larger spectral separation was more accurate and the result was more reproducible using thicker image reconstructions.

Impact of iterative reconstructions on image noise and low-contrast object detection in low kVp simulated abdominal CT: a phantom study

BACKGROUND

Low kilovoltage (kVp) computed tomography (CT) may be used to reduce contrast medium dose in patients at risk of contrast nephropathy, at the cost of increased image noise.

PURPOSE

To evaluate: (i) the impact of iterative reconstructions (Siemens SAFIRE) on low-contrast object detection to compensate for increased noise instead of increased tube loading when decreasing tube potential; and (ii) the change in iodine attenuation in simulated abdominal CT.

MATERIAL AND METHODS

A phantom was scanned at 70, 80, 100, and 120 kVp at fixed effective tube loading (170 mAsEFF) and fixed radiation dose (CTDIVOL 10 mGy). Images were reconstructed with filtered back-projection (FBP) and SAFIRE strengths S1-S5. Iodine attenuation, objective image noise, contrast-to-noise ratio (CNR), noise power spectrum (NPS), spatial resolution, and subjective detectability of low-contrast objects were evaluated.

RESULTS

Compared with 120 kVp iodine attenuation increased by a factor 1.6 and 2.0, and image noise increased by a factor 1.9 and 2.5 at 80 and 70 kVp, respectively. Compared with FBP, SAFIRE showed objective reduction in image noise and increased CNR without loss of spatial resolution or any significant NPS alteration, with general tendency to improve subjective detectability of low-contrast objects. At 170 mAsEFF the number of discernible 1.0% contrast objects at 70 kVp/S5 and 80 kVp/S5 was similar to that at 120 kVp/FBP.

CONCLUSION

With the SAFIRE algorithm image noise, CNR and detectability of low-contrast objects may be kept unchanged without increased tube loading when using low kVp settings to reduce contrast medium dose in azotemic patients.

Ultra-low iodine concentrations iso-attenuating with diagnostic 0.5M gadolinium in endovascular procedures to minimize the risk of contrast nephropathy: A phantom study

PURPOSE

To establish the concentrations of iodine contrast media (I-CM) iso-attenuating with 0.5M gadolinium contrast media (Gd-CM), regarded diagnostic in catheter angiography and vascular interventions in azotemic patients, at various X-ray tube potentials with correlation to skin radiation dose.

MATERIALS AND METHOD

20-mL syringes filled with 30, 40, 50, 70 and 90 mgI/mL, 0.5M Gd-CM and air were placed in a water-equivalent phantom and exposed at about 50, 60, 70, 80 and 90 kV in an X-ray angiographic system. Relative contrast between the contrast materials and the background phantom material was measured on a PACS workstation. Radiation entrance dose, measured with a dose meter and estimated from the dose-area-product (DAP), was adjusted for radiation backscatter to simulate absorbed skin dose.

RESULT

The iodine concentrations 30, 40, 50, 70 and 90 mg/mL resulted in the same relative contrast as 0.5M gadolinium at 53, 57, 62, 71 and 85 kVp, respectively. Air had lower relative contrast than all iodine concentrations at all kVp-settings except for 30 mgI/mL above 84 kVp. The measured skin radiation dose was less than 1 mGy per exposure at all kVp-settings, and around 25-30% lower than the dose estimations derived from the angiographic system's in-built DAP meter.

CONCLUSION

Low-kilovoltage X-ray technique and ultra-low concentrations of I-CM iso-attenuating with 0.5M Gd-CM may be utilizable in peripheral arteriography and endovascular interventions, to minimize the total CM-dose to avoid CIN in azotemic patients.

Analysis of intra-aneurysmal flow for cerebral aneurysms with cerebral angiography

BACKGROUND AND PURPOSE

Hemodynamics is an important factor in the development and rupture of cerebral aneurysms. Current techniques for measuring blood flow in cerebral aneurysms suffer from various limitations and have not been able to address our clinical needs. A new technique has been developed for effective evaluation of intra-aneurysmal flow based on high-frame-rate cerebral angiography, especially for flow-diverters.

MATERIALS AND METHODS

Six patients with 7 unruptured ICA aneurysms were imaged with a specially designed DSA protocol (a 3D DSA and a 2D DSA acquired at 30 frames/s, with a 2-mL/s contrast injection rate). Images of these cases were analyzed to determine the intra-aneurysmal flow based on the newly developed technique. Patient-specific aneurysm models were used for CFD calculation, and intra-aneurysmal flow rates were computed numerically. The intra-aneurysmal flow rates from the 2 methods were then compared.

RESULTS

There is a linear relationship between intra-aneurysmal flow ratios obtained from high-frame-rate cerebral angiography and CFD calculation (R = 0.99). A high frame rate (30 frames/s) provides a better estimate of intra-aneurysmal flow than low frame rates (7.5 frames/s and 15 frames/s).

CONCLUSIONS

The CFD calculation validates the estimate of intra-aneurysmal hemodynamics from cerebral angiography. The linear relationship obtained by using these 2 techniques can be used for real-time assessment of intra-aneurysmal hemodynamics for cerebral aneurysms.