Throughput KPIs for MRI and CT
Improving workflows on MRI and CT requires metrics that are clearly defined and reproducible from existing data. This article introduces the most important ones.
Utilisation
Section titled “Utilisation”Definition: occupied scanner time relative to available scanner time.
- Available time should be clearly defined: regular operating hours minus scheduled maintenance.
- Distinguish planned utilisation (according to the appointment book) from actual utilisation (according to modality timestamps). The difference shows how well planning and reality match.
Exam duration
Section titled “Exam duration”It pays to separate several time spans:
- Scan time: from the first to the last image acquisition, derivable from DICOM headers.
- Room time: from entering to leaving the exam room, including positioning and preparation. Often only available from RIS statuses or additional recording.
- Changeover time: time between the end of one exam and the start of the next.
Durations are rarely normally distributed. Median and percentiles describe them better than the mean, because a few very long exams distort the average considerably.
Slot fit
Section titled “Slot fit”Definition: deviation of actual room time from the planned slot length, per exam type.
Slots that are systematically too short lead to growing delays through the day; slots that are systematically too long lead to unused scanner time.
Waiting time on the day
Section titled “Waiting time on the day”Definition: time between the appointment (or arrival, if later) and the actual start of the exam.
- Evaluated by time of day, it shows whether delays are building up.
- Arrival time is often recorded imprecisely; this should be considered when interpreting results.
Start punctuality
Section titled “Start punctuality”Definition: share of exams starting within a defined tolerance of the appointment time. The tolerance should be defined in advance and applied consistently.
Lead time
Section titled “Lead time”Definition: time between booking and the appointment date. It describes the wait for an appointment and should be considered separately by exam type and urgency.
No-shows and cancellations
Section titled “No-shows and cancellations”Definition: share of appointments not attended or cancelled at short notice. Whether and how freed-up slots are refilled belongs in the same view.
Data sources and pitfalls
Section titled “Data sources and pitfalls”| Source | Provides | What to watch out for |
|---|---|---|
| Modality DICOM headers | study, series and acquisition times, protocol names | clock synchronisation of scanners, inconsistent protocol naming |
| RIS | appointments, exam types, status timestamps | statuses are often set manually and late |
| Scheduling system | planned slots, booking | later rebookings overwrite the original plan |
Reliable metrics require linking the sources and cross-checking them for plausibility. How we do this in projects is described on scan durations.