Last Day

My elective placement in PET / CT has come to end. I am very grateful for the support of the PET / CT team who have answered questions so patiently (sometimes the same question attenuation correction was very confusing !). The last day was full of patient challenges, for instance a patient who had been unable to endure MRI and needed to see the scanner and be reassured, a patient who had recent major resection of a tumour and now faced the possibility of recurrence and was angry, a patient who had endured chemo and become needle phobic and had very difficult veins, a nervous patient who was hard to keep in the rest room after the radioisotope injection, a patient who confused by the instructions started to remove all their clothing (the room camera monitor was turned off). Working in PET / CT has certainly brought home to me how the patients prior experiences of imaging and treatment impact on their behaviour. Also that patients facing a health crisis need to be supported with good explainations, reassurance and patience.

Patient Pathway

Thought I'd give an overview of the patient pathway to PET / CT
Before the scan
PET / CT is not typically part of first line diagnostic imaging. Typically patients will already have had plain film, CT and a biopsy. Some patients will have had or be having chemotherapy. There is no waiting list to speak of with the scan being conducted within a few days of the request, for patient convenience and transport arrangements. Many patients will have travelled a considerable distance to get to the facility.
Prep
The patient is fasted for 6 hrs before the scan so the FDG glucose analogue is taken up by the body.
Clerking
The scan is explained to the patient and detailed medical history taken. This is very relevant to the scan results and helpful to the reporting radiologist. For instance a recent injury or biopsy could lead to FDG uptake in that area.
Cannulation
The patient is has a three way cannula inserted and blood taken for a glucose check. If the glucose level is over 10 mm/ml the FDG will not be taken up by the bodies tissues and the scan must be delayed until it falls.
Radiopharmaceutical
The FDG is drawn up in the lab and the activity checked. Typically this will be 380 - 400MBq in a 0.5 to 2ml injection. The quantity injected varies because the activity level falls over time, the half life being only 2 hours. The FDG is injected via the cannula with the syringe and injection site being flushed with 15 to 20ml of saline (hence the 3 way cannula). The cannula is removed. No medication or contrast is given.
Resting
Each patient has their own small waiting room with an examination couch and chair. They rest quietly for one hour, magazines and a radio are provided. Once the patient is injected they are radioactive and it is explained beforehand that the staff need to keep a distance. The patients are in a room on their own, with a call button and are monitored with CCTV.
Scanning
Just prior to the scan the patient empties their bladder and removes jewellery or garments containing metal, a gown is offered. The patient lies supine on the examination table and enters the scanner head first. Other than the patient being straight and having their arms loosely above their head there is no special positioning requirement. The time the radiographer spends helping the patient onto the couch and positioning them is minimal. Usually directions are given from several steps back and the patient is encouraged to get on the examination table without direct assistance (to minimise staff radiation dose). The radiographer then steps up to the patient checks the head is straight in the foam support, positions a knee support, puts a blanket on the patient, reminds them to keep still and leaves.
Protocol
With the patient's details already on the system a CT Tomogram maps the patients position and length (required to plan how many beds are needed for the PET scan). The CT scan, low dose, takes 30 seconds. CT scans are head first with the patient going in and out of the scanner twice (for Tomo and CT scan). The PET scan is from thighs up (or feet if it is a total body scan). The patient is advanced through the scanner then comes back through feet first. A typical scan takes 35 minutes and is whole body (mid thigh to vertex). Each bed (or section and there are usually 8 in total) takes 3 to 5 minutes. The patient moves through the scanner advancing by one bed length at time. PET bed length is how the body is spilt up into overlapping sections of about 30cm for scanning. A very tall patient might be measured at 9 bed lengths and child might be 7 bed lengths. The patient is monitored through a small thick lead glass window, though I've read lead glass is not very effective for 511Kev gamma rays and some centres use CCTV.
After scanning
The blanket and knee support are removed and the patient encouraged to get off the table safely. Once again this is done from a distance, (it feels so weird to stand back). The patient is directed to the changing facilities and reminded to eat and drink normally, when results are to be expected and being radioactive to keep a distance from pregnant women and small children for 6 hours. If transport was organised it is usually chased at this point.
Processing
Once aquired the images are processed and the CT / PET fused. Copies are made to CD.
Reporting
The images are reported by radiologists within 48 hrs, often on the day of scanning or the following morning. Recent CT and MRI scans and reports are also viewed. The reporting is painstaking and takes at least half an hour per patient (with some taking longer). The PET is viewed first for an overall assessment. The CT is viewed axially moving from vertex down and fusing the image with PET to examine any unusual appearances. NB viewing the CT as a moving image was challenging but I found it very helpful for anatomy revision.

case studies PET / CT

Two very different cases really served to underline how helpful PET / CT can be. Both patients had a SPN (solitary pulmonary nodule) identified on a chest X ray. Both went for CT and the SPN was confirmed. Needle biopsy was inconclusive so both patients were referred for PET. One patient had no areas of increased FDG uptake, indicating a benign nodule. The other patient had significant uptake around the perimeter of the SPN. A repeat biopsy will be performed but this time guided by the PET findings the perimeter of the nodule will be sampled. As the TNM classification was T2N0M0 the nodule should be suitable for resection (depending on the histology). These patients were unusual in that before the PET scan there was only a possibility of cancer. Many of the patients already know (from prior histology) and some have only just received the news. The staging of the cancer that PET makes possible will often determine if curative treatment is possible and the patients are often fully aware of this.

Learning about PET / CT

It has been a real advantage during my time in PET / CT to have a Radiographer also new to PET / CT present. Key PET / CT competencies in PET / CT are in their Clinical portfolio, which Radiographers new to this modality complete. The radiographer has also been kind enough to bring in their notes from a recently completed PET / CT training course (the first formal course in the country apparently). This has given me a real insight into my learning and how it fits into the skills profile required of radiographers in this modality.
A substantial number of radiographers have recently been employed by this major provider of PET / CT which reflects the increasing demand for this imaging modality. In an article by Ell, P.J. (2005) it is noted that the first PET / CT was installed in a hospital in 2001, by 2005 200 had been sold worldwide. When I visited this particular site in May they were doing 4 to 5 scans a day they are now doing 6 to 7 and in just over a year have exceeded 1000 scans. Since availability has been an obstacle to student radiographers experiencing PET / CT the trend is certainly encouraging. Given the major impact of PET / CT in the investigation of cancer in particular it is also great news for patients.

Thoughts on PET / CT

In many ways this has been an excellent PBM choice. Each day up to 7 PET / CT examinations are done here on a range of conditions (mainly oncology but this is a proven strength of PET). The team here have worked hard to involve us in every aspect of PET imaging.
It is though challenging to fully involve students. There are some pretty significant obstacles to getting hands on experience. The potential radiation hazard to staff, especially those who are not fully trained and experienced, dwarfs most other applications of ionising radiations. Patient anxiety is probably the highest I've ever experienced. Not every patient is scared of the result of the scan but many are. This places huge demands on the staff and their communication.
On the other hand I've learned so much including:- understanding PET to an extent that I was nowhere near before, which has also given new insight into nuclear med, CT and radiation safety, improving knowledge of oncology and cross sectional anatomy and a big jump in medical terminology knowledge. It's also given insight into how clinical objectives are designed that will be useful in my future practice. Mmmm ....

PET / CT Scan Reporting

Got the opportunity today to join a radiologist reporting on PET / CT scans. We had the whole spectrum from numerous areas of high uptake to normal uptake patterns. It was very helpful, and pretty handy for revising cross sectional anatomy.

Safety and PET / CT

We had a bit of a demo with a geiger counter to illustrate the importance of distance to maintaining staff safety when using PET. You probably remember that the annihilation photons are emmitted at 511KeV. With the geiger measuring background radiation at 18 counts per second the count a couple of feet from the patient was over 600 counts per second (one hour after the initial injection). So minimising time with the patient and maximising distance are all important. After learning to get close to patients this feels very odd !