Pediatric Interventional Neuroradiology: "How I Do It" v. I - Diagnostic Angiography

Pediatric neurointervention differs from the adult in several important respects. Here we describe a modern approach to readily acquire diagnostic quality images of children. Preparation, access, angiogragraphy and closure have evolved along with new knowledge and technology. This timely "how I do it" series addresses each topic utilizing literature review and our own experience over 35 years.

Removal of Antiscatter Grids for Spinal Digital Subtraction Angiography: Dose Reduction without Loss of Diagnostic Value

Background Spinal digital subtraction angiography (DSA) exposes patients and operators to substantial amounts of radiation. Antiscatter grid (ASG) removal is used to decrease radiation exposure but may reduce image quality. Purpose To determine whether ASG removal during spinal DSA in adults reduces radiation dose while maintaining diagnostic image quality and whether dose reduction is related to body mass index (BMI). Materials and Methods This Health Insurance Portability and Accountability Act-compliant prospective study included adults undergoing spinal DSA between January and December 2016. Each procedure included an additional angiographic acquisition performed twice, once with and once without ASG, either documenting the artery of Adamkiewicz (no pathology group) or the condition leading to the procedure (pathology group). Dose differences between study acquisitions and the influence of BMI were evaluated via paired t test. Two neurointerventionalists blinded to acquisition protocols were asked to independently evaluate a sample of 40 study acquisitions (20 with ASG, 20 without ASG) from 20 randomly selected participants to (a) rate image quality, (b) categorize findings, and (c) determine whether images had been obtained with or without ASG. Percentage agreement on image quality, findings categorization, and ability to correctly identify the acquisition protocol was calculated for both readers. Results Fifty-three participants (mean age ± standard deviation, 51 years ± 15.2; 32 men) were evaluated. ASG removal reduced the mean dose per acquisition by approximately 33% (mean dose-area product and air kerma decreased from 202 to 135.6 µGy/m² and from 35.3 to 24 mGy, respectively; P < .001) independently of BMI (P = .3). Both readers evaluated all images (40 of 40) as being of diagnostic quality and correctly categorized findings in 19 of 20 (95%) cases. Overall percentage agreement for correct protocol identification was 60% (12 of 20) for grid-in and 45% (nine of 20) for grid-out images. Conclusion Antiscatter grid removal during spinal digital subtraction angiography decreased participants' radiation exposure while preserving diagnostic image quality. © RSNA, 2020.

Feasibility of ultra-low radiation dose digital subtraction angiography: Preliminary study in a simplified cerebral angiography phantom

INTRODUCTION

The objective of this article is to evaluate the feasibility of cerebral digital subtraction angiography (DSA) using ultra-low radiation dose settings in a simplified cerebral angiography phantom.

MATERIALS AND METHODS

We created a silicone phantom capable of producing a simplified cerebral DSA. A total of 18 DSA sets were obtained with gradual six-step reduction of the detector entrance dose (DED) from 1.82 to 0.08 μGy per frame, while standard, postprocessing algorithm (PPA) and copper filter (0.3 mm) with PPA (CwP) algorithm reconstruction protocols were applied. We quantitatively compared their signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) and qualitatively analyzed the images' qualities in terms of image sharpness, contrast, and noise as investigated by five observers.

RESULTS

The SNR and CNR, which decreased with lowering of the DED in the standard protocol group, were significantly compensated by using the PPA. The values were approximately double in the PPA (11.5 ± 2.9) and CwP (11.0 ± 2.5) groups compared with the standard (5.4 ± 1.1) group in the DED of 0.24 μGy per frame as well as in the other values. The total scores of the observers according to the protocols showed a tendency to decrease as the DED lowered. On average, the PPA (96.3 ± 34.6) and CwP (91.3 ± 29.9) groups yielded higher results than the standard protocol (83.7 ± 46.7).

CONCLUSION

Given that the current DED ranges from 1.82 to 3.60 μGy per frame for routine cerebral DSA, our results indicate that DED can be decreased to 15%-30% of the current dose level in vessels 2-4 mm in diameter if image-improvement algorithms are applied.

Optimisation in fluoroscopy

Optimisation of radiation protection in fluoroscopy is important since the procedure could lead to relatively high absorbed doses both in patients and personnel resulting in acute radiation injury. Optimisation procedures include adjustment of the fluoroscopy equipment such as exposure factors as well as proper use of automatic brightness control and pulsed fluoroscopy. It is also important to gain the benefits of image processing and the higher sensitivity of flat panel detectors as compared to image intensifier-TV systems.

Proper positioning of the patient with respect to detector and X-ray tube is of fundamental importance to image quality and radiation dose to the patient. Both image quality and radiation dose are also affected by the methodology used with parameters such as magnification factor, increased filtration, use of last-image-hold and the use of a grid.

There is a direct relation between patient dose and the absorbed dose to the personnel since this is mostly due to scattered radiation from the patient. If the correct methodology and the correct radiation protection devices are used, the absorbed dose to the personnel could be minimised to acceptable levels even for those working with complex procedures.

In order to have an organised review of all aspects of optimisation, it is recommendable to have an active quality system at the department. This system should define responsibilities and tasks for persons involved.

Radiation injuries after fluoroscopic procedures

Fluoroscopically guided diagnostic and interventional procedures have become much more commonplace over the last decade. Current fluoroscopes are easily capable of producing dose rates in the range of 0.2 Gy (20 rads) per minute. The dose rate often changes dramatically with patient positioning and size. Most machines currently in use have no method to display approximate patient dose other than the rough surrogate of total fluoroscopy time. This does not include patient dose incurred during fluorography (serial imaging or cine runs), which can be considerably greater than dose during fluoroscopy. There have been over 100 cases of documented radiation skin and underlying tissue injury, a large portion of which resulted in dermal necrosis. The true number of injuries is undoubtedly much higher. The highest dose procedures are complex interventions such as those involving percutaneous angioplasties, stent placements, embolizations, and TIPS. In some cases skin doses have been in excess of 60 Gy (6000 rads). In many instances the procedures have been performed by physicians with little training in radiation effects, little appreciation of the radiation injuries that are possible or the strategies that could have been used to reduce both patient and staff doses. Almost all of the severe injuries that have occurred were avoidable.