CT Head Dose Reduction Using Spiral Scanning Protocol Reed, William J MD; Broderick, Daniel F, MD; Weindling, Steven M, MD; Czervionke, Leo F MD; and Morin, Richard L; PhD; Mayo Clinic, Department of Radiology; Jacksonville, Florida
INTRODUCTION Radiation dose received from diagnostic imaging continues to be a concern as the number of studies performed continues to increase In addition, many patients undergo multiple studies including follow-up exams and imaging for multiple comorbidities Thus, it is essential to continue to attempt to reduce dose; however, image quality must be maintained at a level that allows diagnoses to be reliably made
BACKGROUND Dose Index Registry (DIR) data from 2 nd quarter of 2012 revealed the mean Computed Tomography Dose Index (CTDI VOL ) for CT Brain without contrast (CT Brain w/o) to be 57mGy Data included 207 DIR sites across the country Mayo Clinic (Jacksonville) reported a mean CTDI VOL of 73 mgy Current max limit for CTDI VOL for CT Brain w/o is 75 mgy
PURPOSE To reduce mean CTDI VOL for CT Brain w/o examinations while maintaining diagnostic quality images.
METHODS Current protocol used at our institution for CT brain w/o involves axial scanning with an average CTDI VOL of 73mGy. This study evaluated spiral scanning for CT brain w/o with an estimated CTDI VOL of 62 mgy; this represents a reduction of approximately 15%. Approach was broken into 2 phases: Phase 1 selection of protocol Phase 2 selection of kernel
METHODS: PHASE 1 A list of trial protocols that altered pitch and current (mas) was chosen in conjunction with the site physicist. Phase 1 began with 8 protocols A test phantom was scanned using the protocols Round table discussion with 3 board certified neuroradiologists, site physicist, and CT technologists narrowed the scope to 4 protocols
METHODS: PHASE 1 Channels (Active Detectors) Pitch CTDI VOL (mgy) 64 0.55 62 64 0.8 62 20 0.55 65 20 0.8 65 Automatic exposure control (AEC) was utilized which explains the constant CTDI VOL with change in pitch (the software alters the ma to obtain relatively constant CTDI VOL Collimation for all 4 protocols was constant at 0.06
METHODS: PHASE 1 3 board certified neuroradiologists independently reviewed the images and ranked them from best to worst in two categories: Spatial resolution Contrast Radiologists were blinded to the protocols.
METHODS: PHASE 1 The protocol with the highest score was selected. At this point, the protocol variables were revealed to the group. The Radiologists all agreed that the selected protocol produced images of diagnostic quality The protocol was implemented on a two week trial period in patients being followed for normal pressure hydrocephalus.
METHODS: PHASE 2 Post processing consisted of 3 different kernels for each study performed in the 2 week period At the end of the two week period, the radiologists ranked the kernels in order of preference. The kernel with the highest score was selected. The group unanimously agreed to proceed with the transition from axial to spiral scanning without concern for sacrificing diagnostic image quality.
RESULTS Implementation of the new spiral scanning protocol reduced CTDI VOL from 73 mgy to 62 mgy, a reduction of approximately 15% This protocol was subsequently implemented for all routine CT Brain examinations (with and without contrast)
CONCLUSIONS As the number of CT scans continues to increase, reducing radiation dose while maintaining quality diagnostic images will remain extremely important. This project showed that protocols can be improved by using a logical, systematic approach It is our hope that this project will lead to further improvements in dose reduction throughout the department, including other modalities We must remain vigilant in continually improving our imaging protocols to better serve our patients.