Optimizing CT Image Quality - Part 4 - CARE kV

Optimizing CT Image Quality CARE kV     Walter Huda, PhD Professor of Radiology Medical University of South Carolina   Adjusting Voltages Operation Features Without Exposure Control Fixed kV Fixed Effective mAs With CARE Dose4D Fixed kV Quality Reference mAs ↓ Fixed kV Effective mAs With CARE Dose4D and CARE kV Reference kV Quality Reference mAs ↓  Actual kV Effective mAs CARE kV Optimization of kV to minimize patient dose at maintained Image Quality Increasing X-ray Tube Voltage (kV) More X-rays More Penetration Adjusting kV affects: Contrast + Noise CARE kV Requires Diagnostic Task Non-contrast Contrast enhanced CT Angiography       Contrast enhanced - 7   Non-contrast - 3 Contrast enhanced - 7   Non-contrast - 3 Contrast enhanced - 7 CT Angiography - 11 CARE kV Identifies task (user) Computes lesion versus kV Computes noise versus kV Computes Contrast to Noise Ratio CNR “Controlled” → Adjusting mAs mAs adjusted → equalize CNR kV and mAs → “Dose” “Optimal kV” → “Lowest Dose” Protocol Defines Quality Reference mAs Reference kV Diagnostic Task Never Adjust for an Individual Patient CARE kV Example → → “Low Z” (Soft Tissue) “High Z” (Iodinated Contrast) CARE Dose4D (140 kV) Quality Reference mAs 80 [CTDIvol 10 mGy] ← mAs (& CTDIvol) reduced to ~25% in small phantom → → CARE Dose4D + CARE kV Non-contrast setting: 3 ← Same “Soft Tissue” CNR Similar CTDIvol CT Angiography setting: 11 → Same “Iodine” CNR CTDIvol↓ 65% @ 80 kV Display Window Grouping Semi kV mode Changing kV Changes Contrast   Fully Assisting Scanner Technologies (FAST)   Without FAST Window With FAST Window     Multi-Phase CT Study Arterial & Venous Phase (7) → 100 kV Non-Contrast Phase (3) → 140 kV Link Series Forces “single kV” CARE kV Identifies Optimum kV Links Series Semi kV MODE Investigate CTDIvol/mAs For Different kV Dose Savings/Penalties 120 kV → 80 kV Constant CNR Dose ↓ 25% Follow up Study REQUIRES Same kV as Initial Scan Operator Selects and Fixes kV FAST (Fully Assisting Scanner Technologies) CARE Combined Applications to Reduce Exposure CARE kV CARE Dose4D CARE Profile Adjusting Voltages CARE kV + CARE Dose4D - Identifies Optimal kV - Selects Effective mAs - Maintains Image Quality (CNR) Operation Requires Diagnostic Task Identifies the optimal tube that minimizes dose Angiographic studies dose savings much greater than non contrast enhanced examinations Features FAST Windows Grouping/Linking Semi kV mode