Module 2 · The Journey of a Scan

Overview

A scan is not a single event. It starts with a clinician's question and ends, if all goes well, with an answer that changes the patient's care. In between, it passes through many people and several computer systems. This lesson follows Mr. Diaz's CT pulmonary angiogram (CTPA) from start to finish. Module 3 then shows where AI tools plug into this same path. About 15-20 minutes. New terms are in the Module 2 glossary (opens in a new tab).

By the end of this lesson you can:

Describe the nine steps of a scan's journey, from order to follow-up.
Name the main computer systems (EHR, RIS, PACS) and what each one does.
Explain why the reason for the exam on the order matters so much.
Recognize the steps where errors and delays most often happen.
State the two rules that close the loop: critical results need a direct call, and follow-up recommendations need an owner.

Radiology informatics 101: how radiology data travels

Radiology informatics is the study and running of the computer systems that move radiology information: orders, images, reports and results. You will hear these names on your first day in any hospital. Each is a separate piece of software, often from a different company, and they pass messages to each other.

EHR (electronic health record)The patient's main chart: notes, medicines, lab results, orders. Where clinicians order scans and read reports.

RIS (radiology information system)Radiology's own scheduling and tracking system. Knows which exams are booked, done and reported.

PACS (picture archiving and communication system)Stores every image and shows them on the radiologist's workstation. The image files you meet in Lesson 2.3 live here.

WorklistThe radiologist's to-do list of exams waiting to be read, sorted by urgency and time.

Reporting systemWhere the radiologist writes the report, usually by speaking into a microphone with speech recognition, using templates.

These systems talk using shared standards. DICOM carries images (more in Lesson 2.3). HL7 (Health Level Seven) carries text messages such as orders and reports. FHIR (Fast Healthcare Interoperability Resources, said "fire") is a newer, web-style version of HL7 that many apps, and many AI tools, now use to read from the EHR.

Put together, one scan's data travels in a loop. The order starts in the EHR and goes to the RIS as an HL7 message. The RIS books the exam and sends the patient's details to the scanner's own worklist, so the images are labeled with the right name and exam. The scanner sends the images to PACS as DICOM files, and the exam appears on the radiologist's worklist. The radiologist reads it in PACS, dictates the report in the reporting system, and the signed report travels back through the RIS to the EHR, where the ordering clinician and, often, the patient read it. A break at any link (a wrong name on the order, images that never reach PACS, a report that never reaches the chart) is a break in patient care.

Follow Mr. Diaz's scan

Step through the journey. The map shows which system is involved at each step.

Interactive: the journey of a scan

1. Order

EHR

A clinician decides a scan is needed and enters an order in the EHR. The order names the exam and gives the reason for exam (also called the indication or clinical history): the question the scan should answer. Many EHRs now check the order against guidelines, such as the ACR Appropriateness Criteria, and flag tests that are unlikely to help. This is called clinical decision support.

Mr. Diaz: the ED doctor orders "CT angiogram chest, PE protocol. Reason: sudden shortness of breath and right pleuritic chest pain after a 14-hour flight; D-dimer elevated." (A D-dimer is a blood test that is high when the body is breaking down clots.)

2. Protocol and schedule

RIS

The order crosses to the RIS. A radiologist or technologist protocols it: chooses exactly how the scan will be done (which body part, with or without contrast, the timing of the contrast). The exam is then scheduled. Emergencies go to the front of the line.

Mr. Diaz: protocolled as a CTPA, with contrast timed to fill the lung arteries. His kidney blood test is normal and he has no contrast allergy, so the scan is cleared.

3. Scan

Scanner

The technologist checks the patient's identity with two identifiers (such as name and date of birth), confirms the exam, explains it, places an IV line if contrast is needed and runs the scan. The scanner builds a series of images (Lesson 2.3 looks inside them).

Mr. Diaz: scanned at 01:40. The contrast injection makes him feel warm all over for a few seconds, which is normal. The scan takes about ten seconds.

4. Store and send

Scanner → PACS

The scanner sends the DICOM images to PACS, where they are stored and matched to the order using the accession number. If the images are labeled with the wrong patient or order, they can end up in the wrong chart.

Mr. Diaz: about 600 images in four series arrive in PACS within a couple of minutes.

5. Worklist

Worklist

The exam appears on a radiologist's worklist. Exams are sorted by priority: STAT (urgent, now), then urgent, then routine. A busy overnight list may hold dozens of exams. Where an exam sits in the queue decides how fast it gets read.

Mr. Diaz: his exam is marked STAT from the ED and goes near the top of the overnight list.

6. Read

PACS

The radiologist opens the study on a PACS workstation. They read the reason for exam, look at any prior (earlier) imaging for comparison, then scroll through every series in several windows, looking at everything on the images, not only the question asked.

Mr. Diaz: the overnight radiologist sees a clot in a branch of the right lower lobe pulmonary artery. Checking the lung window, they also notice an 8 mm nodule in the right upper lobe. He has no prior CT to compare with.

7. Report

Reporting

The radiologist dictates a report, often from a template, and signs it. Overnight, a resident may write a preliminary report that an attending radiologist later confirms or corrects as the final report. Lesson 2.4 walks through this report line by line.

Mr. Diaz: report dictated by 02:05: acute pulmonary embolism, no strain on the heart, and an incidental lung nodule with a recommendation for follow-up CT. The radiologist holds the signature until after the phone call in step 8, so the call can be recorded in the report.

8. Communicate

Reporting → EHR

The signed report goes to the EHR, where the ordering team and often the patient can read it. A critical result (a finding that needs action right away, like a PE) is not left to wait in the chart: the radiologist phones the team directly, often before the report is signed, and documents who they spoke to and when.

Mr. Diaz: the radiologist calls the ED doctor at 02:07, adds the call to the report and signs it at 02:10. Blood thinners (anticoagulants) are started within the hour.

9. Follow-up

EHR → RIS

Some findings need more imaging later. Someone has to read the recommendation, tell the patient, and order and schedule the next scan. This is the step most likely to be dropped, especially when the finding is incidental (not related to the reason for the scan) and the patient changes doctors or leaves the hospital.

Mr. Diaz: the PE is treated, and he goes home after three days. The nodule needs a CT in 6-12 months. Will anyone remember? Many hospitals now run tracking programs, with a nurse navigator or software, to catch these.

Why the order matters

The reason for exam is the radiologist's only window into the patient. They usually have not met the patient and see the order long before the full chart. A good reason for exam changes how the scan is done (the protocol) and what the radiologist looks for.

Weak reason for exam	Better reason for exam
"Chest pain"	"Sudden right pleuritic chest pain and shortness of breath after a long flight; D-dimer elevated. Assess for PE."
"Rule out pathology"	"Right lower abdominal pain for 1 day, fever, white count 15. Appendicitis?"
"Headache"	"Sudden worst headache of life 2 hours ago, on blood thinners. Bleed?"

The ACR Appropriateness Criteria are guidelines from the American College of Radiology that rate which test is best for a given clinical problem. They are what the decision support in step 1 is usually built on.

How to Order Diagnostic Imaging (Joseph W. Owen, MD) Watch on YouTube

Getting the Indication Correct (Joseph W. Owen, MD) Watch on YouTube

Put it in order

Interactive: put the steps in order

Drag the steps into the order they happen. Then check. (With a keyboard: focus a step and use the up and down arrows.)

The radiologist reads the images and compares with priors
The exam is protocolled and scheduled in the RIS
The radiologist phones the team about the critical result, then signs the report
The images are sent to PACS and matched to the order
The clinician enters an order with a reason for exam
A follow-up CT is booked for the lung nodule
The exam appears on the worklist, marked STAT
The technologist checks identity and runs the scan
The radiologist dictates the report

Where things go wrong

Most imaging errors are not a radiologist missing something on the picture. Many happen before the scan or after the report. Knowing the steps helps you see where.

Interactive: what went wrong?

Each story is a real type of error. Decide at which step it happened.

Wrong sideA CT of the left knee is ordered, but the patient's pain is in the right knee.

Order. Laterality (side) errors on orders are common. Technologists confirm with the patient before scanning, which catches many.

Contrast too earlyThe CTPA images are taken before the contrast reaches the lung arteries. They are too dark to judge.

Scan. Poor contrast timing makes a CTPA "non-diagnostic," and the scan may need to be repeated, with more radiation and more contrast.

Nobody calledA report showing a collapsed lung is signed at night, but nobody phones the team. They see it the next morning.

Communicate. Critical results need a direct call, documented in the report. A signed report alone is not enough.

Lost noduleA report recommends a follow-up CT for a lung nodule. The patient is discharged, and two years later the nodule is a cancer.

Follow-up. This is the classic dropped handoff, and the reason for tracking programs. It could happen to Mr. Diaz.

"Rule out pathology"A vague reason for exam leads to the wrong protocol, and the scan cannot answer the real question.

Order. The radiologist can only protocol and read for the question they are given.

Wrong patientTwo patients with the same last name; the wrong one is scanned.

Scan. This is why technologists use two identifiers every time.

Two rules that close the loop

Two of the stories above failed after the radiologist had done the read correctly. Both failures have a simple rule against them.

1. Critical results need a direct call

A finding that needs action now, such as a PE, a collapsed lung or a bleed in the brain, is never left to sit in the chart. The radiologist phones the treating clinician, the clinician repeats it back ("read-back"), and the call is written into the report: who, when and what was said. If the ordering doctor cannot be reached, the radiologist keeps going up the chain until someone who can act has been told.

2. Follow-up recommendations need an owner

A recommendation in a report does nothing on its own. A named person has to tell the patient, order the next scan or hand the task over clearly, and put it in the discharge summary. By default that is the ordering physician's team. Tracking programs are a safety net, not a replacement for an owner.

For the ordering physician

Three habits help most: write a real reason for exam, read the whole report (not only the first line), and when a report recommends follow-up, make sure someone owns it before the patient leaves. Make sure the radiology department can reach you, or whoever covers for you, when a critical result comes in.

Where AI fits (a preview)

Every step on the map is a place a computer could help, and AI tools already exist for most of them: suggesting a protocol, cleaning up noisy images, moving suspected critical findings to the top of the worklist, flagging findings during the read, drafting parts of the report, and tracking follow-up recommendations. Each one changes the journey in a different way, and each can fail in a different way. Lesson 3.1 maps these tools onto the journey you just learned.

Knowledge check

Answer each question to continue. Any answer is fine; read the explanation.

Which system stores the images and shows them on the radiologist's workstation?

PACS (picture archiving and communication system) stores and displays images. The EHR is the patient's chart; the RIS schedules and tracks radiology exams.

The radiologist finds Mr. Diaz's PE at 2 a.m. What should happen besides signing the report?

A PE is a critical result. It needs direct, documented communication so treatment starts right away.

Which step of the journey is most often where an incidental finding gets lost?

Recommendations for later imaging depend on someone reading, owning and scheduling them. Handoffs between teams make this the weakest step.

Key takeaways

A scan's journey has nine steps: order, protocol and schedule, scan, store and send, worklist, read, report, communicate, follow-up.
The EHR holds the chart, the RIS schedules and tracks, PACS stores and shows images. They talk through DICOM, HL7 and FHIR.
The reason for exam shapes both how the scan is done and what the radiologist looks for.
Critical results need a direct call. Follow-up recommendations need an owner.
Many errors happen before the scan or after the report, not only during the read.

Go further (optional)

ACR Appropriateness Criteria (look up "suspected pulmonary embolism" and see how the tests are rated)
How to Order Diagnostic Imaging (Joseph W. Owen, MD, YouTube)

Next lesson: the report is signed. What does it say, and how do you read it?